U.S. Department of Energy

Energy Effi ciency and Renewable Energy

Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable

Building Technologies Program

T OF ENERGY

DEPARTMEN

U

E

NITED STAT S OFA ERICA

M

March 2005 • NREL/SR-550-37664

Introduction to Building Systems Performance: 

Houses that Work II. Revised February 2005

Building Science Consortium

Westford, Massachusetts

Prepared under Subcontract No. KAAX-3-32443-01
March 2005 • NREL/SR-550-37664 

Introduction to Building 

Systems Performance: 

Houses That Work II. Revised 

February 2005 

January 2003–December 2003

Building Science Consortium 

Westford, Massachusetts 

NREL Technical Monitor: Bob Hendron 

Prepared under Subcontract No. KAAX-3-32443-01 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
 

iii

Table of Contents 

Executive Summary .................................................................................................................... vii 

Preface........................................................................................................................................viii 

Definitions .................................................................................................................................... xi 

Introduction: House Design Recommendations by Climate....................................Introduction - 1 

 Our New Hygro-Thermal Regions.....................................................................Introduction - 2 

Section 1. Houses That Work for Hot-Humid Climates .......................................................1-1 

 Introduction ..........................................................................................................................1-1 

 Building America Best Practices for Hot-Humid Climates....................................................1-1 

Process: Building Design, Systems Engineering, and Commissioning..........................1-2 

Site: Drainage, Pest Control, and Landscaping ............................................................1-3 

Foundation: Moisture Control and Energy Performance ................................................1-3 

Envelope: Moisture Control and Energy Performance ...................................................1-4 

Mechanicals / Electrical / Plumbing................................................................................1-4 

 Building Profile #1: The Houston .....................................................................................1-6 

 Building Science Details.................................................................................................1-7 

 Climate-Specific Details .................................................................................................1-9 

 Field Experience Notes ................................................................................................1-12 

 Material Compatibility and Substitutions ......................................................................1-14 

 Building Profile #2: The Maitland ..................................................................................1-16 

 Building Science Details...............................................................................................1-17 

 Climate-Specific Details ...............................................................................................1-20 

 Field Experience Notes ................................................................................................1-22 

 Material Compatibility and Substitutions ......................................................................1-24 

 Building Profile #3: Orlando SIPs House......................................................................1-25 

 Building Science Details...............................................................................................1-26 

 Climate-Specific Details ...............................................................................................1-28 

 Field Experience Notes ................................................................................................1-30 

 Material Compatibility and Substitutions ......................................................................1-30 

 Building Profile #4: The Montgomery ............................................................................1-32 

 Building Science Details...............................................................................................1-33 

 Climate-Specific Details ...............................................................................................1-36 

 Field Experience Notes ................................................................................................1-38 

 Material Compatibility and Substitutions ......................................................................1-40 

 Table 1: Building Materials Property Table....................................................................1-41 
 

iv

Table of Contents (continued) 

Section II: Houses That Work for Cold Climates..................................................................2-1 

 Introduction ..........................................................................................................................2-1 

 Building America Best Practices for Cold Climates..............................................................2-2 

Process: Building Design, Systems Engineering, and Commissioning..........................2-2 

Site: Drainage, Pest Control, and Landscaping ............................................................2-3 

Foundation: Moisture Control and Energy Performance ................................................2-3 

Envelope: Moisture Control and Energy Performance ...................................................2-4 

Mechanicals / Electrical / Plumbing................................................................................2-4 

 Building Profile #5: The Chicago......................................................................................2-6 

 Building Science Details.................................................................................................2-7 

 Climate-Specific Details ...............................................................................................2-10 

 Field Experience Notes ................................................................................................2-12 

 Material Compatibility and Substitutions ......................................................................2-13 

 Building Profile #6: The Denver......................................................................................2-15 

 Building Science Details...............................................................................................2-16 

 Climate-Specific Details ...............................................................................................2-19 

 Field Experience Notes ................................................................................................2-21 

 Material Compatibility and Substitutions ......................................................................2-23 

 Building Profile #7: The Minneapolis .............................................................................2-25 

 Building Science Details...............................................................................................2-26 

 Climate-Specific Details ...............................................................................................2-28 

 Field Experience Notes ................................................................................................2-29 

 Material Compatibility and Substitutions ......................................................................2-32 

Section III: Houses That Work for Mixed-Humid Climates ..................................................3-1 

 Introduction ..........................................................................................................................3-1 

 Building America Best Practices for Mixed-Humid Climates................................................3-2 

Process: Building Design, Systems Engineering, and Commissioning..........................3-2 

Site: Drainage, Pest Control, and Landscaping ............................................................3-3 

Foundation: Moisture Control and Energy Performance ................................................3-3 

Envelope: Moisture Control and Energy Performance ...................................................3-4 

Mechanicals / Electrical / Plumbing................................................................................3-4 

 Building Profile #8: The Charlotte ....................................................................................3-6 

 Building Science Details.................................................................................................3-7 

 Climate-Specific Details ...............................................................................................3-10 

 Field Experience Notes ................................................................................................3-13 

Material Compatibility and Substitutions ......................................................................3-14 
 

v

Table of Contents (continued) 

 Building Profile #9: The Atlanta......................................................................................3-16 

 Building Science Details...............................................................................................3-17 

 Climate-Specific Details ...............................................................................................3-20 

 Field Experience Notes ................................................................................................3-22 

Material Compatibility and Substitutions ......................................................................3-24 

 Building Profile #10: The Louisville ...............................................................................3-26 

 Building Science Details...............................................................................................3-27 

 Climate-Specific Details ...............................................................................................3-30 

 Field Experience Notes ................................................................................................3-33 

Material Compatibility and Substitutions ......................................................................3-35 

Section IV: Houses That Work for Hot-Dry / Mixed- Dry Climates......................................4-1 

 Introduction ..........................................................................................................................4-1 

 Building America Best Practices for Hot-Dry/Mixed-Dry Climates .......................................4-2 

Process: Building Design, Systems Engineering, and Commissioning..........................4-2 

Site: Drainage, Pest Control, and Landscaping ............................................................4-3 

Foundation: Moisture Control and Energy Performance ................................................4-3 

Envelope: Moisture Control and Energy Performance ...................................................4-4 

Mechanicals / Electrical / Plumbing................................................................................4-4 

 Building Profile #11: The Albuquerque............................................................................4-6 

 Building Science Details.................................................................................................4-7 

 Climate-Specific Details .................................................................................................4-9 

 Field Experience Notes ................................................................................................4-11 

Material Compatibility and Substitutions ......................................................................4-14 

 Building Profile #12: The Sacramento ...........................................................................4-16 

 Building Science Details...............................................................................................4-17 

 Climate-Specific Details ...............................................................................................4-20 

 Field Experience Notes ................................................................................................4-22 

Material Compatibility and Substitutions ......................................................................4-24 

 Building Profile #13: The Tucson ...................................................................................4-26 

 Building Science Details...............................................................................................4-27 

 Climate-Specific Details ...............................................................................................4-29 

 Field Experience Notes ................................................................................................4-31 

Material Compatibility and Substitutions ......................................................................4-33 

Appendix A: Unvented Roof Summary Article.................................................................... A-1 

Appendix B: Sand Layers Should Not Be Placed Between Polyethylene 

Vapor Barriers and Concrete Floor Slabs................................................................. B-1 

Appendix C. Summary of Building Profiles.......................................................................... C-1 
 

vi
 

vii

Executive Summary 

The U.S. Department of Energy’s (DOE) Building America Program is reengineering new and 

existing American homes for energy efficiency, energy security, and affordability. Building 

America works with the residential building industry to develop and implement innovative 

building energy systems—innovations that save builders and homeowners millions of dollars in 

construction and energy costs. This industry-led, cost-shared partnership program has the 

following goals: 

• Reduce whole-house energy use by 40-70% and reduce construction time and waste 

• Improve indoor air quality and comfort 

• Integrate clean onsite power systems 

• Encourage a systems engineering approach for design and construction of new homes 

• Accelerate the development and adoption of high performance residential energy 

systems. 

In 2001, the Building America Building Science Consortium (BSC) developed the Web-based 

Houses That Work (HTW) as a climate-specific technical resource for designing and building 

homes that use 30% less energy or space conditioning and hot water than the 1995 Model Energy 

Code (MEC). That resource reflected the experience gained from 5 years of Building America 

teamwork, including insights gained during the construction of more than 8,000 production 

homes from across the country. Houses That Work was, and is, a freely accessible learning 

resource and reference for builders, building product manufacturers, building researchers, and the 

general public. 

Houses That Work II (HTWII) is more comprehensive and more detailed than the original HTW 

and represents the latest BSC experience and results under the Building America program. 

Specifically, HTWII includes the following: 

• Updated North American hygro-thermal regions map that is aligned with the Department 

of Energy climate zones and map proposed for the International Energy Conservation 

Code (IECC) 

• Climate-specific Best Practices with performance criteria for high-performance home 

design and construction 

• Three Building Profiles per climate 

• A Building Materials Property Table populated with technical and performance 

specifications from product manufacturers and building research members of the BSC. 

This report has five sections—an overall HTWII introduction and four sections explaining the 

four most important hygro-thermal regions: Hot-Humid, Mixed-Humid, Cold, and HotDry/Mixed-Dry. The introduction contains the hygro-thermal map, and each climate section 

contains Best Practices and three Building Profiles. HTWII in its entirety is also available on the 

BSC web site (www.buildingscience.com/housesthatwork). HTWII is also replete with electronic 

building science references. Simply click on the URL from the BSC web site to access the 

resource.
 

viii

Preface 

This report is a combination of principles, technical information, and graphic design/construction 

details driven by two systems: the physical and the legal. 

The Physical System 

The laws of physics (generally) and building science (specifically) are, pardon the expression, 

“cast in concrete”; that is, they define or express an order of things. These laws can be ignored 

but, ultimately, cannot be broken or changed. Think of the example of gravity—it’s not just a 

good idea, it’s the law. You can “ignore” it, but almost always at your peril. 

For Houses That Work, this means understanding and managing the way that four things move on 

or through homes: 

• Water 

• Vapor 

• Air 

• Heat. 

The Houses That Work Best Practices and Building Profiles focus on these four phenomena. 

Builders who follow the guidance provided can create high-performance homes that are safe, 

healthy, durable, comfortable, and economical to operate. 

The Legal System 

These laws were developed to give an order to things—they are “man-made,” sometimes 

arbitrary, and always changeable. These laws can be broken but, ultimately, cannot be ignored. 

Think of the example of speeding—you can break the speeding limit no trouble at all, but you do 

so at some legal risk. Sooner or later the speed limit will require your attention. Because houses 

are among our most durable and valuable goods, we are pretty interested in how we build them to 

manage long-term risk or legal liability. Houses That Work is about the design and construction 

of high-performance homes for managing just such risk and liability. 

How these Two Systems Tie Together in Houses That Work 

Understanding and honoring the physical system can determine how much time and money you 

or your company will have to spend understanding and dealing with the second. This may 

involve some increase in initial costs, but is also likely to reduce at least the potential for longterm liability costs. Basically, it’s the “pay now or pay later” order of things. It’s not a given that 

your first costs will increase when applying the best building science, but it is a given that 

considering your long-term costs along with your initial costs is a great way to manage the 

hazards associated with the legal system. And as a bonus, understanding and honoring the 

physical system almost always results in valuable and durable products—such as your home—

becoming even more valuable and durable. 
 

ix

As with most situations in life, Houses That Work holds true to three well-known proverbs: 

• The devil is in the details 

• Everything is connected to everything else 

• It depends. 

Accordingly, Houses That Work is subject to the following: 

• Contains a lot of technical information and details for what we believe are functional and 

practical building profiles 

• Is based on systems engineering and goes to great lengths to express how changing one 

element of an assembly or system can affect other elements of the same assembly or 

system 

• Gives climate-specific guidance, with precipitation, temperature, and humidity being 

factors upon which the nature and make-up of buildings are most dependent. 

Having said this, there is no way that the information provided in Houses That Work can be 

considered as anything but guidance, nor should the details here be lifted directly into project 

drawings or specifications. The information is not intended to replace professional engineering, 

professional design, professional judgment, or common sense. And just as design, material 

selections, and construction details may change from one climate zone to the next, local 

environmental factors in your specific location or even on one particular lot can lead to changes 

not covered in any particular Houses That Work building profile. 

To bolster your own professional judgment and building common sense, we offer the following 

ten building science principles to keep in the front and back of your head as you use Houses That 

Work to guide you in building high-performance homes. It should not be a surprise that all of 

these principles are at least indirectly related to moisture. Even in hot-dry climates, moisture 

events related to occupant activities, leaks, and singular climate events can bedevil the 

performance and durability of today’s homes. 

1. Our efforts to save energy and reduce the flow of heat through building assemblies have 

reduced drying potentials and, therefore, increased the importance of controlling moisture 

flow through building assemblies. 

2. Ideally, building assemblies should be designed to dry to both the interior and exterior. In 

heating climates, the primary drying potential is to the exterior (but not necessarily 

exclusively so); in cooling climates, the primary drying potential is to the interior (but not 

necessarily exclusively so); and in climates with both heating and cooling, some drying 

potential in both directions is typically a good idea (but not necessarily exclusively so). 

3. Building materials last longer when their faces are exposed to similar or equal 

temperature and humidity. This is why the ventilation of claddings, particularly those that 

store moisture (reservoir claddings), can be important. 

4. Drainage planes, air barriers, and thermal barriers must be continuous to be truly 

effective. Being able to trace each of these on a full elevation drawing without lifting 

your finger (or pencil or pointer) from the elevation is a good test of continuity. 

5. In moisture control, the priority is liquid water first, particularly when it comes in the 

forms of rain and groundwater. In these forms it is referred to as “bulk” water. Following 

are air-transported vapor and then diffusive vapor, all other things being equal. It’s 

always a question of quantities and rates, of wetting and drying, and the tolerance of 

materials (individually and in combination) for each and all of the above. 
 

x

6. Three things destroy materials in general and wood in particular: water, heat, and ultraviolet radiation. Of these three, water is the most important by an order of magnitude. 

7. When the rate of wetting exceeds the rate of drying, accumulation occurs. 

8. When the quantity of accumulated moisture exceeds the storage capacity of the material 

or assembly, problems occur. 

9. The storage capacity of a material or assembly depends on time, temperature, and the 

material itself. 

10. The drying potential of an assembly decreases with the level of insulation and increases 

with the rate of air flow (except in the case of air flow in severe cold climates during cold 

periods where interior moisture levels are high). 
 

xi

Definitions 

ADA Airtight Drywall Approach 

AP Air permeability (ASTM E2178-01) 

ASTM American Society for Testing and Materials 

BA Building America 

BSC Building Science Consortium 

cfm cubic feet per minute 

CGSB Canadian General Standards Board 

DOE U.S. Department of Energy 

EPS Expanded Polystyrene 

ERV Energy-Recovery Ventilation 

FS Flame Spread (ASTM E84) 

HDD Heat Degree Days 

HPR Hydrostatic Pressure Resistance (AATCC127)

HRV Heat-Recovery Ventilation 

HSPF Heating Seasonal Performance Factor 

HTW Houses That Work 

HTWII Houses That Work II 

HVAC Heating, Ventilation, and Air-Conditioning 

ICC International Code Council 

IECC International Energy Conservation Code 

MEC Model Energy Code 

MERV Minimum Efficiency Reporting Value 

OSB Oriented Strand Board 

perm Building Science Consortium definition: a perm is a 

unit of measurement that reflects how readily water 

vapor passes through a material of a certain 

thickness. A material with a perm rating less than 1 is 

considered impermeable, greater than 1 but less than 

10 perms is considered vapor semi-permeable, and 

greater than 10 perms is considered vapor permeable 
 

xii

Definitions (continued) 

RH Relative Humidity 

SD Smoke Development (ASTM E84) 

SHGC Solar Heat Gain Coefficient 

SNAPSHOT Short Non-Destructive Approach to Provide 

Significant House Operation Thresholds 

TIP Termite Infestation Problem 

WA Water Adsorption (ASTM C209) 

w/c water to concrete ratio 

XPS Extruded Polystyrene 
 

Introduction - 1

Introduction: House Design Recommendations by Climate 

Buildings should be suited to their environments. We have accepted that design and construction 

must be responsive to varying seismic risks, wind loads, and snow loads. We also consider soil 

conditions, frost depth, orientation, and solar radiation. Yet we typically ignore the variances in 

temperature, rainfall, exterior and interior humidity, and their interaction. 

Building envelopes and mechanical systems should be designed for a specific hygro-thermal 

region (Map 1), rain exposure (Map 2), and interior climate. While there are similarities among 

hygro-thermal regions, there may also be important differences as a result of annual rainfall. It is 

cold and dry in Wyoming; it is cold and somewhat wet in Wisconsin. Therefore, significantly 

different design and construction practices would be called for in these two states. The Building 

Science Consortium (BSC) design recommendations are based on the hygro-thermal regions with 

reference to the annual rainfall. Local climate must be addressed if it differs significantly from the 

climate described for a particular design. 

Our recommendations are based on our experience with what 

works and what does not work, from forensic investigations of 

building failures, and from the results of test houses and 

thousands of houses constructed by builder partners of the 

Building America (BA) program. These design recommendations are the starting point for a 

thoughtful approach to designing a specific house in a specific location and climate, often for a 

specific purpose. We include the reasoning behind our selection of different envelope assemblies 

for different climates. We also discuss the greatest risks for moisture-related problems in each 

specific design. 

A house is a system of inter-related systems and materials. Consequently, a change in one 

component might have dramatic, even catastrophic, effects on the performance of that assembly 

or the house as a whole. In each of the Building Profiles, we discuss the critical elements in the 

envelope that should be altered only with detailed understanding of the effects that follow the 

change. To learn more about how a slight change in a wall assembly can have disastrous 

consequences for a house and the builder, go to the article on Brick Veneer, Rain, and Sun at 

www.buildingscience.com/resources/walls/brick_veneer_rain_sun.pdf. 

Cost is usually a factor in designing and building houses, especially affordable houses. Every 

project has a budget. Nevertheless, durability and its value to the owner should not be jeopardized 

just to save a few dollars on construction costs. We point out ways in which the recommended 

houses can be made even more robust at some additional cost. The designer, builder, and future 

owner will have to decide how much more to spend for a house that performs better and longer. 

Houses That Work (HTW) consists of three sets of guidance: Best Practices, Building Profile, and 

the Building Materials Properties Table. These are briefly described here. 

Best Practices 

Based largely on BSC Building America Performance Targets (available at the BSC web site 

www.buildingscience.com/buildingamerica/targets.htm), the Best Practices lay out the general 

principles and performance objectives for designing and constructing high performance homes in 

a given climate. 
 

Introduction - 2

Building Profiles 

The Building Profiles presented in this report are representative constructions consisting of the 

following: 

• A cross-sectional drawing 

• Building science details 

• Climate-specific details 

• Field experience notes, and 

• Material compatibility and substitutions.

The Building Materials Property Table 

This table lists nearly 50 of the most common building materials with performance specifications, 

such as vapor permeability, that support the selection or the substitution of building materials 

based on building science and overall performance of the envelope system. 

The first two sets of guidance, Best Practices and Building Profiles, contain many links to other 

BSC technical resources that BSC staff and production builder partners use for more detailed 

follow-up instruction or explanation. 

Used in concert, the Houses That Work elements provide a comprehensive and detailed technical 

resource on climate-specific residential construction. 

Our New Hygro-Thermal Regions 

Climate-specific design and construction of high-performance homes is a cornerstone of all BSC 

work. With BSC input, Building America recently modified the criteria and North American 

climate map defining the eight hygro-thermal regions (Map 1). The changes are not drastic, but 

they are important because they make our criteria and map more consistent with the boundaries of 

the Climate Zones proposed by the Department of Energy (DOE) for the International Energy 

Conservation Code (IECC), and approved in September 2003 by the International Code Council 

(ICC): www.energycodes.gov/implement/pdfs/color_map_climate_zones_Mar03.pdf. Whenever 

the building science community and the code community get on (literally) the same page, this is 

good news for builders of any homes, but particularly those that build climate-tuned, highperformance homes. 

Here is how the two maps align: 

• New Hot-Humid region DOE Proposed Climate Zones 1, 2A, 3A below the 

warm-humid line, and 2B below the warm-humid line 

(“A” represents the “moist” portion of the DOE 

temperature zones, and “B” represents the “dry” 

portion). 

• New Hot-Dry region DOE Proposed Climate Zones 3B, plus 2B above the 

warm-humid line. 

• New Mixed-Humid region DOE Proposed Climate Zones 4A, plus 3A above the 

warm-humid line. 
 

Introduction - 3

• New Marine region DOE Proposed Climate Zones 3C and 4C 

• New Mixed-Dry region DOE Proposed Climate Zone 4B 

• New Cold region DOE Proposed Climate Zones 5 and 6 

• New Severe Cold region DOE Proposed Climate Zone 7 

• New Subarctic/Arctic Region DOE Proposed Climate Zone 8. 

Map 1-1. The New Building America Hygro-Thermal Regions 
 

Introduction - 4

Map 1-2. Annual Precipitation 
 

Introduction - 5

DOE assigns specific locations to climate zones based the county in which the site is located. 

These county assignments may be found on the Building America web site 

(www.eere.energy.gov/buildings/building_america). However, the following approximate 

definitions of each climate region have been developed based on heating degree-days, average 

temperatures and precipitation:

New: Subarctic/Arctic2 

A subarctic and arctic climate is defined as a region with approximately 12,600 heating degree 

days (65°F basis)3 or more. 

New: Very Cold 

A very cold climate is defined as a region with approximately 9,000 heating degree days (65°F 

basis)4 or more and fewer than approximately 12,600 heating degree days (65°F basis). 

 (Previously this was called Severe Cold, which was a defined as a region with approximately 

8,000 heating degree days or more.) 

New: Cold

A cold climate is defined as a region with approximately 5,400 heating degree days (65°F basis)5

or more and fewer than approximately 9,000 heating degree days (65°F basis)6

. 

(Previously this was called Cold, which was a climate is defined as a region with approximately 

4,500 heating degree days or more and fewer than approximately 8,000 heating degree days.) 

New: Mixed-Humid 

A mixed-humid climate is defined as a region that receives more than 20 in. (50 cm) of annual 

precipitation (Map 2), has approximately 5,400 heating degree days (65°F basis)7 or fewer, and 

where the average monthly outdoor temperature drops below 45°F (7°C) during the winter 

months. 

(Previously this was called Mixed-Humid, which was a climate defined as a region that receives 

more than 20 in. of annual precipitation, has approximately 4,500 heating degree days or less 

and where the average monthly outdoor temperature drops below 45°F during the winter 

months.) 

New: Hot-Humid 

A hot-humid climate is defined as a region that receives more than 20 in. (50 cm) of annual 

precipitation and where one or both of the following occur: 

• A 67°F (19.5°C) or higher wet bulb temperature for 3,000 or more hours during the 

warmest 6 consecutive months of the year; or 

 

2

 BSC has not yet developed climate-specific building science guidance for the new Subarctic/Arctic region. 3

 Celsius: 7,000 heating degree days (18°C basis) 4

 Celsius: 5,000 heating degree days (18°C basis) 

5

 Celsius: 3,000 heating degree days (18°C basis) 

6

 Celsius: 5,000 heating degree days (18°C basis) 

7

 Celsius: 3,000 heating degree days (18°C basis)
 

Introduction - 6

• A 73°F (23°C) or higher wet bulb temperature for 1,500 or more hours during the warmest 

6 consecutive months of the year.8

(Previously this was called Hot-Humid, which was a climate defined as a region that receives 

more than 20 in. of annual precipitation and where the monthly average outdoor temperature 

remains above 45°F throughout the year.)

New: Hot-Dry and Mixed-Dry 

A hot-dry climate is defined as a region that receives less than 20 in. (50 cm) of annual 

precipitation and where the monthly average outdoor temperature remains above 45°F (7°C) 

throughout the year. 

A mixed-dry climate is defined as a region that receives less than 20 in. (50 cm) of annual 

precipitation, has approximately 5,400 heating degree days (50° F basis) or less, and where the 

average monthly outdoor temperature drops below 45°F (7°C) during the winter months. 

On the new DOE climate map, this includes zones 2B, 3B, and 4B. 

(Previously this was called: Hot-Dry/Mixed-Dry, which is a climate defined as a region that 

receives less than 20 in. of annual precipitation and where the monthly average outdoor 

temperature remains above 45°F throughout the year. 

A mixed-dry climate is defined as a region that receives less than 20 in. of annual precipitation. 

New: Marine9

A marine climate meets all of the following criteria: 

• A mean temperature of coldest month between 27°F (–3°C) and 65°F (18°C) 

• A warmest month mean of less than 72°F (22°C) 

• At least 4 months with mean temperatures more than 50°F (10°C) 

• A dry season in summer. The month with the heaviest precipitation in the cold season has 

at least three times as much precipitation as the month with the least precipitation in the 

rest of the year. The cold season is October through March in the Northern Hemisphere 

and April through September in the Southern Hemisphere. 

Note: Don’t forget that it is always the conditions that you actually experience in your area that 

determine the appropriate building design and construction details. The Building America 

Climate Zones provide simplified groupings of geographic locations that may actually vary 

greatly in terms of weather, and therefore should be viewed as guidelines. 

 

8

 These last two criteria are identical to those used in the ASHRAE definition of warm-humid climates 

and are very closely aligned with a region where the monthly average outdoor temperature remains 

above 45°F (7°C) throughout the year. 

9

 BSC has not yet developed climate-specific building science guidance for the new Marine region. In 

the interim, guidance provided in the HTWII Mixed-Humid climate generally applies. 
 

1-1

I. Houses That Work for Hot-Humid Climates 

Introduction 

For the purpose of defining best practices in this report, a hot-humid climate is considered a region that 

receives more than 20 in. of annual precipitation and where one or both of the following conditions 

occur:1

• A 67°F (19.5°C) or higher wet bulb temperature for 3,000 or more hours during the warmest 6 

consecutive months of the year, or 

• A 73°F (23°C) or higher wet bulb temperature for 1,500 or more hours during the warmest 6 

consecutive months of the year. 

The intense solar radiation in this climate imposes a large thermal load on the house that can increase 

cooling costs and affect comfort. The approach presented in HTWII minimizes the impact of solar 

radiation on the building, its mechanical system, and its occupants. 

Moisture is a significant problem in this climate, more so in those areas that receive more than 40 in. of 

annual precipitation. The ambient air has significant levels of moisture most of the year. Because air 

conditioning is installed in most new homes, cold surfaces are present on which condensation can occur. 

Controlling the infiltration of this moisture-laden air into the building envelope and keeping moisture 

away from cold surfaces are major goals of design and construction. 

Housing types vary greatly throughout all of the different climate zones, but nowhere is the contrast so 

great as in the Hot-Humid climate of the southern United States. 

In many parts of Florida, block wall assemblies predominate, whereas wood frame is most commonly 

used in Texas. For this reason, we have chosen three different Building Profiles that we think best 

represent the Hot-Humid climate: 

• The “Houston” ―two-story, slab-on-grade, first floor brick veneer, second floor fiber cement lap 

siding, conditioned attic with asphalt shingle roof (Figure 1-1) 

• The “Maitland” ―two-story, slab-on-grade, both floors stucco, conditioned attic, tile roof (Figure 

1-8) 

• The “Orlando SIPs House” ―two-story, slab-on-grade, both floors stucco, conditioned attic, tile 

roof (Figure 1-14) 

• The “Montgomery” ―one-story, conditioned crawlspace, vinyl/aluminum lap siding, unconditioned 

attic, standing-seam metal roof (Figure 1-19). 

A substantial amount of repetition is present in these Building Profiles, but is necessary in order to 

provide comprehensive, stand-alone, examples of performance packages that achieve 40% energy savings 

while maintaining or improving quality and durability. Photographs and a case study for a production 

builder project in a Hot-Humid climate are available on the Building America portion of the Building 

Science Corporation Web site. The case study explores the builder's experience with the Building 

America program and discusses the reasons for the specific design and construction details that are used 

by Pulte Homes in Houston, Texas. Additional information on construction methods and alternative 

designs are included in the EEBA Builder's Guide Hot-Humid Climates and in the EEBA Water 

Management Guide (www.eeba.org/bookstore). 

 

1

 This definition is identical to the ASHRAE definition of warm-humid climates and is very closely aligned with a 

region where the monthly average outdoor temperature remains above 45°F (7°C) throughout the year.
 

1-2

Building America Best Practices for Hot-Humid Climate 

The primary consideration for high-performance Building America homes in hot-humid climates is 

maintaining moisture control both inside the home and within building assemblies, particularly as energy 

conservation shifts the relationship between sensible and latent loads. Reducing solar gain, using energy 

conserving appliances and compact fluorescent lighting, reduces the size of the sensible load relative to 

the latent load. This affects the ability of the air conditioner to remove moisture or dehumidify the air. 

The following Best Practices are based on our Building America Performance Targets 

(www.buildingscience.com/buildingamerica/targets.htm) and are reflected in the four Hot-Humid 

building profiles: the “Houston,” the “Maitland,” the “Orlando SIPs House,” and the “Montgomery.” All 

climate-specific Best Practices are identified with a bolded and bracketed [HH]. 

Process: Building Design, Systems Engineering, and Commissioning 

Design for Energy Performance 

Energy performance for space conditioning and hot water 40% better than the 1995 MEC base case house 

(i.e., equal to 10% better than ENERGY STAR® performance requirements) 

Systems Engineering 

Design structure using advanced framing methods (see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm or 

www.buildingscience.com/resources/presentations/advanced_framing.pdf) 

Design structure to accommodate the most efficient duct distribution system that places all ducts and air 

handling equipment within conditioned space (see 

www.buildingscience.com/resources/misc/wood_efficiency.pdf; specifically Figure 1-4) 

Design and detail structure for durability, in terms of wall and roof assembly drying potential, continuous 

drainage plane, and continuous thermal barrier that clearly defines the conditioned space (see the Building 

Profiles section of this report) [HH] 

Commissioning: Performance Testing 

Air leakage (determined by blower door depressurization testing) should be less than 2.5 in.2/100 ft2

surface area leakage ratio (CGSB [Canadian General Standards Board], calculated at a 10-Pa pressure 

differential); or 1.25 in.2

/100 ft2 leakage ratio (ASTM [American Society for Testing and Materials], 

calculated at a 4-Pa pressure differential); or 0.25 cubic feet per minute/square feet (cfm/ft2

) of building 

envelope surface area at a 50-Pa air pressure differential. If the house is divided into multiple conditioned 

zones, such as a conditioned attic or conditioned crawl space, the blower door requirement must be met 

with the access to the space open, connecting the zones. 

Ductwork leakage to the exterior for ducts distributing conditioned air should be limited to 5% of the total 

air-handling system rated air flow at high speed (nominal 400 cfm per ton) determined by pressurization 

testing at 25 Pa. Two acceptable compliance mechanisms are (1) test duct leakage to outside at finish 

stage or (2) test total duct leakage at duct rough-in stage. 

Forced-air systems that distribute air for heating and cooling should be designed to supply airflow to all 

conditioned spaces and zones (bedrooms, hallways, basements), as well as to provide a return path from 

all conditioned spaces or zones. Interzonal air pressure differences, when doors are closed, should be 

limited to 3 Pa. This is typically achieved by installing properly sized transfer grilles or jump ducts (see 

www.buildingscience.com/resources/mechanical/transfer_grille_detail.pdf and 

www.buildingscience.com/resources/mechanical/transfer_grille_sizing_charts.pdf). 
 

1-3

Mechanical ventilation system airflow should be tested during commissioning of the building. 

Testing of the house should be completed as part of the commissioning process. The SNAPSHOT (Short 

Non-Destructive Approach to Provide Significant House Operation Thresholds) form is available for 

download as a convenient way to record the testing information (see 

www.buildingscience.com/buildingamerica/snapshot_form.pdf). Instructions for completing the form are 

also available (see www.buildingscience.com/buildingamerica/snapshot_instructions.pdf). Unique or 

custom house plans should each be tested. In a production setting, each model type (i.e., floor plan) 

should be tested until two consecutive houses of this model type meet testing requirements. At this point, 

testing on this model type can be reduced to a sampling rate of one in seven (i.e., one test, with six 

"referenced" houses). Small additions to a floor plan (e.g., bay window, conversion of den to bedroom) 

should be considered the same model type; major changes (e.g., bonus room over the garage, conversion 

of garage into casita or hobby room, etc) should be considered a separate model type.

Site: Drainage, Pest Control, and Landscaping 

Drainage 

Grading and landscaping shall be planned for movement of building run-off away from the home and its 

foundation, with roof drainage directed at least 3 ft beyond the building and a surface grade of at least 5% 

maintained for at least 10 ft around and away from the entire structure. 

Pest Control 

Based on local code and Termite Infestation Probability (TIP) maps, use environmentally appropriate 

termite treatments, bait systems, and treated building materials that are near or have ground contact (see 

www.uky.edu/Agriculture/Entomology/entfacts/). [HH] 

Landscaping 

Plantings should be held back as much as 3 ft and no less than 18 in. from the finished structure, with any 

supporting irrigation directed away from the finished structure. Decorative ground cover—mulch or pea 

stone, for example—should be thinned to no more than 2 in. for the first 18 in. from the finished structure 

(see Building Profiles). [HH] 

Foundation: Moisture Control and Energy Performance 

Moisture Control 

The building foundation shall be designed and constructed to prevent the entry of moisture and other soil 

gases (see Building Profiles). [HH] 

Slabs require a 6-mil polyethylene sheeting directly beneath the concrete or an equivalent approach (such 

as rigid insulation) that accomplishes vapor control and capillary control for the slab. The vapor barrier 

must continuously wrap the slab as well as the grade beam. 

Sub-slab drainage where necessary shall consist of a granular capillary break directly beneath the slab 

vapor barrier. 

Use radon resistant construction practices as described on the EPA radon control web site 

(www.epa.gov/iaq/radon/construc.html). 
 

1-4

Energy Performance 

Slabs in this climate are generally not insulated, even at the perimeter, because of the low overall heating 

load (less significant delta-T overall) and code restrictions on below-grade use of rigid foam insulation. 

Local codes and economics permitting, consider the use of borate-treated rigid insulation on the slab 

perimeter (see the Building Profiles and photo detail at 

www.buildingscience.com/buildingamerica/casestudies/fairburn.htm). [HH] 

Envelope: Moisture Control and Energy Performance 

Moisture Control 

Water management. Roof and wall assemblies must contain elements that provide drainage in a 

continuous manner over the entire surface area of the building enclosure, including lapped flashing 

systems at all penetrations. See the Building Profiles or the EEBA Water Management Guide for specific 

details for various wall assemblies. [HH]

Vapor management. Roof and wall assemblies must contain elements that, individually and in 

combination, permit drying of interstitial spaces (see Building Profiles). [HH]

Energy Performance 

Air leakage. Exterior airflow retarder is foam sheathing; interior air-flow retarder is gypsum board 

sealed to the slab and frame walls (Airtight Drywall Approach [ADA]). For details of the ADA for 

interior airflow retarders, see the Building Profiles. [HH]

Windows. We recommend one of two approaches: 

• U-factor 0.35 or lower and SHGC (solar heat gain coefficient) 0.35 or less, regardless of climate 

• Climate and/or orientation-specific glazing properties if the builder can employ passive solar 

orientation and design and if occupants can be expected to operate window shading in concert with 

time of day and weather conditions. [HH]

Mechanicals/Electrical/Plumbing

Systems Engineering

Heating, Ventilation, and Air-Conditioning (HVAC) system design, both equipment and duct, should be 

done as an integral part of the architectural design process.

HVAC system sizing should follow ACCA Manual J, and duct sizing should follow ACCA Manual D 

(see www.buildingscience.com/resources/mechanical/509a3cooling_system_sizing_pro.pdf).

Mechanical ventilation should be an integral part of the HVAC system design (see the Building Profiles 

or www.buildingscience.com/resources/mechanical/advanced_space_conditioning.pdf).

A whole house dehumidification system integral to the air handling system is recommended for this 

climate (see the Building Profiles and 

www.buildingscience.com/resources/mechanical/conditioning_air.pdf). [HH] 

Energy Performance 

Air conditioner or heat pump shall be installed according to best practices; see 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf.
 

1-5

Major appliances meet high-energy efficiency standards using current appliance ratings. Only those 

appliances in the top one-third of the DOE Energy Guide rating scale should be selected. For further 

details, see www.eren.doe.gov/consumerinfo/energy_savers/appliances.html.

Occupant Health and Safety

Base rate ventilation. Controlled mechanical ventilation per ASHRAE Standard 62.2. 

Spot ventilation. Intermittent spot ventilation of 100 cfm should be provided for each kitchen; all kitchen 

range hoods must be vented to the outside (no recirculating hoods). Intermittent spot ventilation of 50 

cfm, or continuous ventilation of 20 cfm when the building is occupied, should be provided for each 

washroom/bathroom.

All combustion appliances in the conditioned space must be sealed combustion or power vented. 

Specifically, any furnace inside conditioned space should be a sealed-combustion 90%+ unit. Any water 

heater inside conditioned space should be power vented or power-direct vented. Designs that incorporate 

passive combustion air supply openings or outdoor supply air ducts not directly connected to the 

appliance should be avoided.

Provide filtration systems for forced air systems that provide a minimum atmospheric dust spot efficiency 

of 30% or MERV (Minimum Efficiency Reporting Value) of 6 or higher.

Indoor humidity should be maintained in the range of 25% to 60% by controlled mechanical ventilation, 

mechanical cooling, or dehumidification (see 

www.buildingscience.com/resources/moisture/relative_humidity_0402.pdf).

Carbon monoxide detectors (hard-wired units) shall be installed (at one per every approximate 1000 ft2

) 

in any house containing combustion appliances or an attached garage.

Information relating to the safe, healthy, comfortable operation and maintenance of the building and 

systems that provide control over space conditioning, hot water or lighting energy use shall be provided to 

occupants.

Envelope/Mechanicals Management 

Plumbing. No plumbing in exterior walls. Air seal around plumbing penetrations in pressure boundary 

(air barrier) such as rim (band) joist or ceiling. 

Electrical. Seal around wires penetrating air barrier or pressure boundary. 
 

1-6

Building Profile #1. The Houston 

Foundation: Slab Attic: Conditioned Cladding (1st floor): Brick veneer 

Above Grade Wall: Wood frame Roof: Asphalt shingles Cladding (2nd floor): Fiber cement siding

Figure 1-1. Cross section of the Houston 
 

1-7

Building Science Details

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions, such as top-ofwall/roof assembly junctions, band joists, and between attached garages and living spaces. These three are 

discussed below because they have proven to be a consistent challenge for builders. 

Top-of-Wall/Roof Assembly Junction 

The continuity of an exterior air barrier can be maintained at this junction if the air barrier material (foam 

insulation or stucco cladding, for example) is used continuously for the wall, soffit, and fascia. The 

continuity of an interior air barrier can be maintained through a combination of cut foam blocks and 

sealant/caulk, or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the 

air barrier. 

Band Joists 

Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped housewrap or 

rigid foam insulation. Continuity of an interior air barrier can be maintained through a combination of cut 

foam blocks and sealant/caulk, or spray foam. Note that neither cellulose nor fiberglass (batt or blown) 

can be used for the air barrier. The air barrier detail on second-story band joists is important because it is 

inaccessible (covered by structural/finish floor and ceiling finish) after construction. The air 

barrier/thermal envelope detail is important on ground floor band joists because of the thermal bridge that 

can occur at the top of crawlspace foundation walls (as the result of the air barrier and thermal envelope 

moving from the outside to the inside of the building envelope and termite inspection zones located at the 

top of crawlspace foundation walls). Note that while fiberglass batts fulfill the requirement for protection 

from ignition in the open band joists, fiberglass batt material by itself cannot maintain the air barrier. 

Attached Garages 

The building envelope surfaces shared between conditioned space and an unconditioned garage must have 

a continuous air barrier. See Figure 1-2 for details in terms of using sealants and rigid insulation to create 

a continuous air barrier between the attached garage and living space. Refer to 

www.buildingscience.com/housesthatwork/airsealing/default.htm for air sealing details. 

Figure 1-2. Creating a continuous air barrier 
 

1-8

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information (www.buildingscience.com/resources ). 

Because the wall and roof assemblies in this building profile have a vapor retarder or vapor barrier on the 

exterior, high vapor permeability of the interior sheathing and finish (gypsum wallboard and latex paint) 

are necessary to facilitate the drying of the wall assembly to the interior. 

Drainage Plane, Air Barrier, and Vapor Control 

In this wall assembly, the 3/8-in. extruded polystyrene (XPS) fan-fold rigid insulation is acting as the 

drainage plane (as well as providing a contribution to the thermal barrier). While the XPS does function 

as a secondary air barrier, the primary air barrier is the interior gypsum board installed using the Airtight 

Drywall Approach. Note that on the second floor cantilever, there is both an interior and an exterior air 

barrier. Sealing the joints between sections of the fiber cement soffit is difficult, so blocking is installed 

and sealed between the floor joists directly above the top plate of the first floor wall. The 1-in. air space 

vented top and bottom by the open head joints provides a mechanism for controlling solar-driven 

moisture from the brick veneer (a reservoir cladding), as does the 3/8-in. XPS fan-fold rigid insulation by 

acting as a vapor barrier and draining condensed moisture. For more information on the phenomenon of 

solar-driven moisture and reservoir claddings, go to 

www.buildingscience.com/resources/walls/solar_driven_moisture_brick.htm. See Field Experience 

Notes for more information on this sheathing and Material Compatibility and Substitutions if you are not 

using this sheathing material. 

Window Flashing 

Window flashing details are wall assembly or cladding specific (Figure 1-3 and EEBA Water 

Management Guide www.eeba.org/bookstore). 

 

Figure 1-3. Window flashings 
 

1-9

Advanced Framing 

An important element of high performance wood-frame construction is an advanced framing package, in 

this case including cross-bracing or some alternative for shear resistance. For more detailed information 

on advanced framing techniques, see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm.

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult, if not impossible, to assess before 

completion of the structure — confined concentrations of air-borne radon, soil treatments (termiticides, 

pesticides) methane, etc. The cost of this "ounce" of prevention is well balanced against the cost of the 

"pound" of cure. Note that this system is a passive system that can easily be converted to an active 

ventilation system by installing an in-line fan in the stack in the attic. 

Thermal Barrier 

In this climate, moisture control does not require specific levels of insulation. Inside/outside temperature 

differences do not require cavity-warming exterior rigid insulation to control wintertime condensing 

surface temperatures. Having said this, insulating sheathing in general is a good idea. We recommend full 

cavity fill in the walls, but the 2-x-6 framing is more about advanced framing than the depth of cavity 

insulation that can be achieved. The R-22 cellulose or R-30 batts in the conditioned attic have proven to 

be adequate to provide interior conditions for enhanced HVAC equipment durability and duct 

performance when these systems are located in the attic. Cellulose netting or fiberglass batt supports 

create an insulation “belly” and accommodate cavity fill depth that exceeds the depth of the truss top 

chord. 

Sub-slab Stone Bed 

The 4-in.-deep 3⁄4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. The sub-slab stone bed is a practical method 

for venting soil gas should it be necessary. 

Climate-Specific Details 

Termite Management 

In hot-humid climates, termites are best managed with a three-pronged approach that deals with the three 

things termites need ― cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building and maintain any 

termite inspection zone on the exterior of the foundation. 

Moisture control. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building and make sure that irrigation is directed away from the building. 
 

1-10

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if for some reason, chemical treatment 

of soil or building materials is not an option, then complete rigor in moisture control and ground cover is 

required. 

Asphalt Shingles and a Roofing Vapor Barrier 

Solar-driven moisture through standard roofing papers under asphalt shingles requires that a vapor 

impermeable roofing underlayment be installed between the asphalt shingles and the structural roof deck. 

See the Building Materials Property Table 

(www.buildingscience.com/housesthatwork/buildingmaterials.htm) for suitable materials. For an in-depth 

discussion of the phenomenon of solar-driven moisture in hot-humid climates in roof assemblies, go to 

www.buildingscience.com/resources/roofs/unvented_roof.pdf. 

Conditioned Attics 

This assembly (Figure 1-4) may require discussion with the local building code official. For further 

information, read the article entitled “Unvented Roof Summary” (Appendix A). 

Mechanical Systems 

The following are key elements of a system for this climate: 

Sealed Combustion Gas Furnace. This provides energy efficiency and health/safety with the unit inside 

conditioned space. 

Figure 1-4. A conditioned attic 
 

1-11

Minimum 12 SEER A/C Unit. This ensures energy efficient management of sensible load. 

Central-fan Integrated Supply Ventilation. This system is simple, effective, and economical. It 

provides fresh, filtered, outside air in a controlled amount using the existing HVAC delivery system for 

even distribution and mixing. Set-up intermittent central-fan integrated supply, designed to ASHRAE 

62.2P rate, with fan cycling control set to operate the central air handler 10 min every hour to provide 

ventilation air distribution and whole-house averaging of air quality and comfort conditions ($125 to 

$150). Include a normally closed motorized damper in the outside air duct with the AirCyclerTM FRV 

control (+$50 to $60). See Appendix B for more detailed information. 

Supplemental Dehumidification. All homes in this climate call for supplemental dehumidification 

because the reduced sensible load of high-performance homes reduces the dehumidification the A/C unit 

provides, extends shoulder seasons, and raises the impact of occupant-generated moisture. The ducted 

stand-alone dehumidifier in the attic controlled by a humidistat located in the living space has proven to 

be the most effective and economical system for the production home building setting. Our recommended 

system (+$300 to $350) includes GE dehumidifier model AHG40FCG1 located in an insulated enclosure 

in the attic and ducted to the living space, Honeywell humidistat model H8808C located in the living 

space, and Honeywell switching relay (with transformer) model RA89A 1074. For a detailed discussion 

of supplemental dehumidification see 

www.buildingscience.com/resources/mechanical/conditioning_air.pdf. 

Ducts in Conditioned Space. The preferred method for keeping HVAC ducts and mechanical equipment 

inside conditioned space is to either move them down from the attic, or move the conditioned boundary 

up (to the underside of the roof sheathing) so that the attic is conditioned as shown in Figure 1-5. In no 

case should HVAC ducts be placed within exterior wall assemblies ― this is not what is meant by ducts 

in conditioned space. A vented attic assembly may be used in this climate as long as the ceiling plane is 

air tight and no ductwork or air-handling equipment is located in the attic. 
 

1-12

Figure 1-6. Transfer grilles and jump ducts 

Transfer Grilles and Jump Ducts. Single air returns require transfer grilles to provide return pathways 

that prevent pressurization of bedrooms. Appropriate sizing for ducts, including these pressure relief 

methods, can be seen in Figure 1-6, with additional information at the BSC web site

(www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf). 

Water Heater. Any type of gas water heater (in terms of venting) is adequate if the water heater is 

located in the garage. If the water heater is located inside conditioned space, then it must be a gas-power 

vented or power-direct vented unit, or an electric water heater. 

Field Experience Notes 

3/8-in. XPS Fan-Fold Rigid Insulation 

In order for this material to function as a drainage plane, all joints must be overlapped or sealed. This thin 

material is easily penetrated―all holes must be sealed. 
 

1-13

Air Sealing 

Unvented assemblies—walls or roofs—are robust when the air sealing is robust. The hardest spots are not 

the fields but the margins/edges of assemblies. Spray foam applied at the margins (truss/rafter end 

blocking) may seem more expensive than cutting in air stops and caulking between each truss or rafter, 

but the labor savings and air sealing quality of spray foam make it a good choice. 

Brick Shelf in Slab Perimeter 

The brick veneer "seat" is readily accomplished by securing dimensional lumber of the desired size to the 

inside top edge of the concrete form. 

Brick Veneer and the Air Space 

Harking back to "old-timer" practices—place a thin sand layer at the bottom of the 1-in. air space (to act 

as a bond break for mortar droppings) and leave bricks out intermittently in the first course. After the 

veneer is completed, the sand and mortar droppings can be easily removed and the missing bottom course 

brick mortared in. Head joints in the top and bottom course must be left clear for top and bottom venting 

of this space. Masons must also be aware of protecting the integrity of the XPS foam sheathing as they 

work, given its function as the wall's drainage plane. Educate this trade with some building science basics 

about the impact of their work on building envelope performance. 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/1619_Yost&Edminster_for_au.pdf. 

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 1-7 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss. 

Figure 1-7. A “slider” truss
 

1-14

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow high 

performance start-up procedures such as the following: 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf.

Fiber-cement Siding 

Getting set up and taking the time to back-prime this material and to prime all cuts may seem like quite an 

added burden, but it enhances the long-term performance of this reservoir cladding. A quick-drying 

primer in a “slop bucket,” lightweight cloth gloves, and disposable foam brush for “dabbing” make it 

manageable. 

Material Compatibility and Substitutions 

Exterior Sheathing/Building "Paper" 

Because the brick veneer is a reservoir cladding, relief from solar-driven moisture must come from the 

free-and-clear 1-in. continuous air space or the vapor impermeable layer just interior to the cladding, or 

both (as is the case in this building profile). The vapor impermeable XPS rigid insulation sheathing can be 

replaced with housewrap and oriented-strand board (OSB), if a free-and-clear 1-in. continuous air space 

between the brick veneer and the rest of the wall assembly is provided and maintained. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that have relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). Because this wall assembly is designed to dry exclusively to the interior, 

do not use any layers in the assembly interior to the exterior sheathing that have low vapor permeability. 

Note that when foam insulation is left exposed in an assembly, a "thermal barrier" or "protection against 

ignition" may be required. Code implementation/interpretation has proven to be particularly troublesome 

for "gray" areas, such as spaces that are conditioned but not occupied (conditioned attics and 

crawlspaces). 

Soffit Material 

Fiber cement material was selected for the soffit because of its robustness with regard to moisture. 

Excellent control of moisture, air, and heat flow is critical at this overhang of interior floor space. 

Flooring 

Many finished flooring materials—either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example)—should only be installed over a slab with a low 

w/c ratio (≅ 0.45 or less) or a slab allowed to dry (<0.3 g/24hr/ft2

) before installation of flooring. In 

general, sheet vinyl flooring should be avoided. 

Sub-slab Sand Layers 

A sand layer (to prevent differential drying and cracking) should never be placed between a vapor barrier 

and a concrete slab. Place the concrete directly on top of the vapor barrier. This problem is better handled 

with a low w/c ratio (≅ 0.45 or less) and water curing of the concrete with wetted burlap or ponding for up 

to 72 hr. 
 

1-15

Vapor Barrier Roofing "Paper" 

Note that it is the combination of reservoir roof cladding and conditioned attic that dictates the low 

permeability roofing underlayment. The roofing underlayment should have a permeability of less than 1 

perm.2

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is critical in hot-humid climates. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, laundry rooms, and kitchens are excellent 

candidates for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s 

DensArmor®, USG’s Fiberock®). In addition, paper-faced gypsum board should never be used as interior 

sheathing or backer for tub or shower surrounds where ceramic tile or marble (any material with joints or 

grout lines) is used as the finish. 

 

2 Building Science Consortium definition: a perm is a unit of measurement that reflects how readily water vapor 

passes through a material of a certain thickness. A material with a perm rating less than 1 is considered 

impermeable, greater than 1 but less than 10 perms is considered vapor semi-permeable, and greater than 10 perms 

is considered vapor permeable.
 

1-16

Building Profile #2. The Maitland 

Foundation: Stem wall & slab Cladding (1st floor): Stucco Cladding (2nd floor): Stucco 

Attic: Conditioned Above Grade Wall (1st floor): Masonry Above Grade Wall (2nd floor): Wood frame 

Roof: Tile

Figure 1-8. Cross section of the Maitland 
 

1-17

Building Science Details 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as top-ofwall/roof assembly junctions, band joists, and between attached garages and living spaces. These three are 

discussed below because they have proven to be a consistent challenge for builders. 

Top-of-wall/Roof Assembly Junction. The continuity of an exterior air barrier can be maintained at this 

junction if the air barrier material (foam insulation or stucco cladding, for example) is used continuously 

for the wall, soffit, and fascia. The continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, or spray foam. Note that neither cellulose nor 

fiberglass (batt or blown) can be used for the air barrier. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, or spray foam. Note that neither cellulose nor 

fiberglass (batt or blown) can be used for the air barrier. The air barrier detail on second-story band joists 

is important because it is inaccessible (covered by structural/finish floor and ceiling finish) after 

construction. The air barrier/thermal envelope detail is important on ground-floor band joists because of 

the thermal bridge that can occur at the top of crawlspace foundation walls (as the result of the air barrier 

and thermal envelope moving from the outside to the inside of the building envelope and termite 

inspection zones located at the top of crawlspace foundation walls). Note that while fiberglass batts fulfill 

the requirement for protection from ignition in the open band joists, fiberglass batt material by itself 

cannot maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 1-9 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. Refer to www.buildingscience.com/housesthatwork/airsealing/default.htm for air-sealing details. 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

Figure 1-9. Using sealants and rigid insulation to create a continuous air barrier 
 

1-18

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information (www.buildingscience.resources).

In both the first and second story wall assemblies, drying can occur to the exterior and the interior as long 

as permeable latex paints are used. The use of semi-permeable rigid insulation on the interior of the first 

story masonry wall assembly allows drying to the interior at a controlled rate. Either expanded 

polystyrene (EPS) or extruded polystyrene (XPS) can be used in this location. We recommend that less 

than 1 in. of XPS be used. A thicker layer retards inward drying too much because of its lower vapor 

permeability. 

Drainage "Step" in Slab Perimeter. 

The block "seat" is readily accomplished by securing dimensional lumber of the desired size to the inside 

top edge of the concrete form. 

Drainage Plane, Air Barrier, and Vapor Control 

The drainage plane on the first story exterior wall is the face of the stucco. The drainage plane on the 

second story exterior wall is the StuccoWrap®. Flashing details at penetrations on each story must reflect 

this difference. The building paper behind the weep screen flashing at the transition from first to second 

story is an important “back-up” protection against liquid water penetration into the wall assembly. The 

first-floor air barrier is the concrete block (with continuity at the top of the wall provided by the cap 

block). On the second floor, the air barrier is both the exterior stucco rendering and the interior gypsum 

board installed using the Airtight Drywall Approach. Control of moisture drive inward from the outside is 

accomplished by the relative impermeability of the OSB on the second story. On the first story, the 

storage capacity and insensitivity of the concrete block mitigates the impact of moisture penetration in the 

wall assembly, and the entire assembly permits drying in both directions. 

Window Flashing 

Window flashing details are wall assembly or cladding specific. See Figure 1-10 and refer to the EEBA 

Water Management Guide (www.eeba.org/bookstore). 

Advanced Framing 

An important element of high performance wood-frame construction is an advanced framing package. For 

more detailed information on advanced framing techniques, see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm.

Framing on Sab 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult if not impossible to assess before 

completion of the structure—confined concentrations of air-borne radon, soil treatments (termiticides, 

pesticides), methane, etc. The cost of this "ounce" of prevention is well balanced against the cost of the 

"pound" of cure. Note that this system is a passive system that can easily be converted to an active 

ventilation system by installing an in-line fan into the stack in the attic. 
 

1-19

 

 Exterior door pan flashing “seat” Window sill drainage detail 

Window sill drainage section 

Figure 1-10. Window Flashings 

Thermal Barrier 

In this climate, moisture control does not require specific levels of insulation. Inside/outside temperature 

differences do not require cavity-warming exterior rigid insulation to control wintertime condensing 

surface temperatures. Having said this, insulating sheathing in general is a good idea. We recommend full 

cavity fill in the walls, but the 2-x-6 framing is more about advanced framing than the depth of cavity 

insulation that can be achieved. The R-22 cellulose or R-30 batts in the conditioned attic have proven to 

be adequate to provide interior conditions for enhanced HVAC equipment durability and duct 
 

1-20

performance when these systems are located in the attic. Cellulose netting or fiberglass batt supports 

create an insulation “belly” and accommodate cavity fill depth that exceeds the depth of the truss top 

chord. 

Sub-Slab Stone Bed 

The 4-in.-deep 3⁄4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. The sub-slab stone bed is a practical method for 

venting soil gas should it be necessary. 

Climate-Specific Details 

Termite Management 

In hot-humid climates, termites are best managed with a three-pronged approach that deals with the three 

things termites need ― cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain the 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor by the others. For example, if for some reason, chemical treatment of 

soil or building materials is not an option, then complete rigor in controlling moisture and ground cover 

must be maintained. 

Conditioned Attics 

This assembly may require discussion with local building code official. See Appendix A for assistance. 

Mechanical Systems 

The following are key elements of a system for this climate: 

Sealed combustion gas furnace. This provides energy efficiency and health/safety with the unit inside 

conditioned space. 

Minimum 12 SEER A/C unit. Provides energy efficient management of sensible load. 

Central-fan-integrated supply ventilation. This system is simple, effective, and economical. It 

provides fresh, filtered, outside air in a controlled amount using the existing HVAC delivery system for 

even distribution and mixing. Set-up intermittent central-fan-integrated supply, designed to ASHRAE 

62.2P rate, with fan cycling control set to operate the central air handler 20 minutes every hour to provide 

ventilation air distribution and whole-house averaging of air quality and comfort conditions ($125 to 

$150). Include a normally closed motorized damper in the outside air duct with the AirCyclerTM FRV 

control (+$50 to $60). See Appendix B for more detailed information. 
 

1-21

Figure 1-11. Dehumidification 

Supplemental dehumidification. All homes in this climate call for supplemental dehumidification 

because the reduced sensible load of high performance homes reduces the dehumidification the AC unit 

provides, extends shoulder seasons, and raises the impact of occupant-generated moisture. The ducted 

stand-alone dehumidifier in the attic controlled by a humidistat located in the living space has proven to 

be the most effective and economical system for the production home building setting. Our recommended 

system (+$300 to $350) includes GE dehumidifier model AHG40FCG1 located in an insulated enclosure 

in the attic and ducted to the living space, Honeywell humidistat model H8808C located in the living 

space, and Honeywell switching relay (with transformer) model RA89A 1074 (Figure 1-11). For a 

detailed discussion of supplemental dehumidification, see 

www.buildingscience.com/resources/mechanical/conditioning_air.pdf.

Ducts in conditioned space. The preferred method for keeping HVAC ducts and mechanical equipment 

inside conditioned space is to either move them down from the attic, or move the conditioned boundary 

up (to the underside of the roof sheathing) so that the attic is conditioned, as shown in Figure 1-12. In this 

building profile, a conditioned attic can be used for HVAC ducts and equipment. In no case should 

HVAC ducts be placed within exterior wall assemblies—this is not what is meant by ducts in conditioned 

space. A vented attic assembly may be used in this climate as long as the ceiling plane is airtight and no 

ductwork or air handling equipment is located in the attic. 

Transfer grilles and jump ducts. Single air returns require transfer grilles to provide return pathways 

that prevent pressurization of bedrooms (Figure 1-12). Appropriate sizing for ducts, including these 

pressure relief methods, can be found at 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

Water heater. Any type of gas water heater (in terms of venting) is adequate if the water heater is 

located in the garage. If the water heater is located inside conditioned space, then it must be a gas power 

vented or power-direct vented unit, or an electric water heater. 
 

1-22

Figure 1-12. Placement of ducts and transfer grilles 

Field Experience Notes 

Air Sealing 

Unvented assemblies—walls or roofs—are robust when the air sealing is robust. The hardest spots are not 

the "fields" but the "margins" of assemblies. Spray foam may seem like an expensive element of the 

assembly, but the labor savings and air sealing quality in comparison to the alternatives make it a good 

choice. 
 

1-23

Roofing 

Roofing tiles in general, and light-colored ones in particular, have proven a wise choice to reduce cooling 

loads in this climate. For more information, see 

www.buildingscience.com/resources/roofs/performance_of_unvented_attics.pdf or the ENERGY STAR®

Reflective Roof Product List at www.energystar.gov/ia/products/prod_lists/roof_prods_prod_list.xls. 

Elastomeric Paints and Stucco 

We have found that acrylic latex paints generally outperform elastomeric paints on stucco. While 

elastomeric paints have excellent crack-spanning capability, they can be much less vapor-permeable than 

acrylic latex paints. Elastomeric paints have been known to blister when moisture gets into the assembly. 

In hot-humid climates, the higher vapor permeability of latex paints is overall more important than the 

higher crack-spanning capability of elastomeric paints unless a high permeability (greater than 20 perms) 

elastomeric paint coating is used. 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Energy Trusses 

A number of different truss configurations yield greater depth at the heel, but they vary quite a bit in cost. 

The truss (Figure 1-13, sometimes called a “slider” truss) has proven to be among the most costcompetitive. And of course, the pitch of the roof affects just how much insulation you can get at this 

location, regardless of the type of truss. 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow high 

performance start-up procedures such as the following: 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf.

Figure 1-13. Energy trusses, also known as a “slider truss” 
 

1-24

Material Compatibility and Substitutions 

Exterior Sheathing/Building "Paper" 

We do not recommend any substitutions behind stucco and a wood-framed wall. The paper-backed lath is 

an excellent bond break for the stucco and the unique corrugated profile of the StuccoWrap® is an 

excellent drainage plane material. In addition, structural sheathing is required for its resistance to wind 

loads in this hurricane-prone region. Note that a cladding/sheathing combination capable of passing the 

hurricane impact test is a critical component of any wall assembly within many areas of this climate 

region. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that have relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). Because this wall assembly is designed to dry exclusively to the interior, 

do not use any layers in the assembly interior to the exterior sheathing that have low vapor permeability. 

Note that when foam insulation is left exposed in an assembly, a "thermal barrier" or "protection against 

ignition" may be required. Code implementation/interpretation has proven to be particularly troublesome 

for "gray" areas, such as spaces that are conditioned but not occupied (conditioned attics and 

crawlspaces). 

Eave Blocking and Spray Foam 

Because stucco is used as the exterior cladding, it can be used continuously on the soffit and fascia 

(replacing the spray foam and blocking) to move the air barrier from the top of the wall to the roof 

overhang (see Hot-Dry/Mixed-Dry Climate Building Profiles). 

Flooring 

Many finished flooring materials—either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example)—should only be installed over a slab with a low 

w/c ratio (≅ 0.45 or less) or a slab allowed to dry (<0.3 g/24hr/ft2

) before installation of flooring. In 

general, sheet vinyl flooring should be avoided. 

Sub-Slab Sand Layers 

A sand layer under the slab (to prevent differential drying and cracking) should never be placed between a 

vapor barrier and a concrete slab. Cast the concrete directly on top of the vapor barrier. This problem is 

better handled with a low w/c ratio (≈ 0.45 or less) and wetted burlap covering during initial curing (see 

Appendix B). 

Latex Paint 

The substitution of low permeability finishes (vinyl wall paper, oil-based paints) for latex paint is strongly 

discouraged because of reduced drying potential. (Note that there are latex paints with very low vapor 

permeabilities, but they are generally clearly labeled as such.) 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, laundry rooms, and kitchens are excellent 

candidates for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s 

DensArmor®, USG’s Fiberock®). In addition, paper-faced gypsum board should never be used as interior 

sheathing or backer for tub or shower surrounds where ceramic tile or marble (any material with joints or 

grout lines) is used as the finish. 
 

1-25

Building Profile #3. The Orlando SIPs House 

Figure 1-14. Cross section of the Orlando SIPS House 

Foundation: Block stem wall and slab Roof Cladding: Metal 

Attic: Cathedral ceilings / conditioned attic Above-Grade Wall: SIPs panel 

Wall Cladding: Cement board siding / brick veneer
 

1-26

Building Science Details 

Air Sealing Details at Transitions 

Air sealing is important at assembly transitions such as 

top-of-wall/roof assembly junctions, SIPS panel joints, 

and between attached garages and living spaces. 

Top-of-Wall / Roof Assembly Junction 

Air-barrier continuity can be provided at this junction if 

sealant is used on the top and bottom of the top plate. 

See Figure 1-15 for an alternative roof framing option 

using SIPS panels. 

SIPS Panel Joints 

Air-barrier continuity can be provided at SIPS panel 

joints with a continuous bead of sealant between foam 

sections and a continuous bead of sealant between the 

plywood or OSB skin panels on the interior (Figure 1-

16). See Figure 1-17 for an alternative above-grade 

wall spline detail. Also note on the cross section the 

wall/floor air-sealing detail between the first and 

second floors. 

Attached Garage 

The building enclosure surfaces shared between 

conditioned space and an unconditioned garage must 

have a continuous air barrier. 

Drying Mechanisms 

In any climate, vapor control is based on the 

relationships among the following: the permeability of 

wall components, the type of cladding (reservoir or 

non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based 

on the relationship between the exterior and interior 

moisture content and temperature differences). The 

type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these 

inter-relationships. 

In both the first- and second-story wall assemblies, 

drying can occur to the exterior and the interior as long 

as permeable latex paints are used. 

Figure 1-16. Sealant locations between panels 

Figure 1-15. Alternative SIPS roof framing 
 

1-27

Drainage Plane, Air Barrier, and Vapor Control 

The primary drainage plane behind both the cement board 

and the brick veneer is the housewrap/weather resistant 

barrier (WRB) over the SIPS panel and the waterproofing 

membrane over the slab and stem wall. Flashing details at 

penetrations must reflect this difference. 

The housewrap/weather resistant barrier (WRB) is an 

important “back-up” protection against liquid water 

penetration into the SIPS panels. On first and second floor, 

the air barrier is the SIPS panel. Control of moisture drive 

from the outside in is accomplished by the relative 

impermeability of the SIPS panel. 

The roofing paper underneath the standing seam metal roof 

has two functions. It serves as a slip surface for the roofing 

for expansion and contraction of the metal, and it serves as 

a secondary drainage plane for moisture that might 

condense on the underside of the metal roofing as the result 

of night-sky radiation and subsequent 

condensation. 

Window Flashing 

Window flashing details are wall assembly or cladding 

specific. See Figure 1-18 for a detail of a load-bearing 

window jamb assembly. 

Framing on Slabs 

Installing a capillary break between the sill plate and a 

concrete slab on all walls—exterior, interior, partition—is 

good practice. A closed-cell foam sill sealer or gasket works 

well. Alternatively, a strip of sheet polyethylene can be used. 

This isolates the framing from any source of moisture that 

may be either in or on the concrete slab (and using sill sealer 

on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are 

difficult if not impossible to assess prior to completion of the 

structure— confined concentrations of air-borne radon, soil 

treatments (termiticides, pesticides) methane, etc. The cost 

of this "ounce" of prevention is well balanced against the 

cost of the "pound" of cure. Note that this system is a 

Figure 1-17: Above-grade wall spline 

Figure 1-18. Load-bearing window 

jamb assembly
 

1-28

passive system that can easily be converted to an active ventilation system by installing an in-line fan into 

the stack in the attic. 

Thermal Barrier 

The foam sandwiched between the plywood skins of the SIPS panels on the walls and roof is the thermal 

barrier. It should be noted that in this climate, moisture control does not require specific levels of 

insulation; but, it does require joints between panels be sealed to control air-transported moisture. 

Inside/outside temperature differences do not require cavity-warming exterior rigid insulation to control 

wintertime condensing surface temperatures. 

Sub-slab Stone Bed 

The 4-in.-deep 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab airpressure field extender for the soil gas ventilation system. The sub-slab stone bed is a practical method for 

venting soil gas should it be necessary. 

Climate-Specific Details 

Termite Management 

In hot-humid climates, termites are best managed with a three-pronged approach that deals with the three 

things termites need―cover from sunlight, moisture, and food (wood or paper). 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2-in. depth for the first 18 in. around the building, and maintain the 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from the building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building-materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Interrelationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor by the others. For example, if for some reason chemical treatment of 

soil or building materials is not an option, then maintain complete rigor in controlling moisture and 

ground cover. 

Conditioned Attics 

As an alternative to cathedral ceilings, a conditioned attic may be constructed to house HVAC equipment 

or be used as additional useful living space. This assembly may require discussion with local building 

code official. See Appendix C for assistance. 

Mechanical Systems 

The key elements of a system for this climate are as follows: 

Sealed-combustion gas furnace. This is necessary for energy efficiency and health/safety with the unit 

inside conditioned space. 

Minimum 12 SEER AC unit. This enables energy-efficient management of sensible load. 
 

1-29

Central-fan-integrated supply ventilation. This system is simple, effective, and economical. It provides 

fresh, filtered, outside air in a controlled amount using the existing HVAC delivery system for even 

distribution and mixing. Set up the intermittent central-fan-integrated supply, designed to ASHRAE 62.2P 

rate, with fan-cycling control set to operate the central air handler as much as 33% of the time, but not 

less than 25% of the time. This should occur at least every 3 hours to provide ventilation air distribution 

and whole-house averaging of air quality and comfort conditions ($125 to $150). Include a normally 

closed motorized damper in the outside air duct with the AirCyclerTM FRV control (+$50 to $60). See 

http://www.buildingscience.com/resources/mechanical/air_distribution.pdf for more detailed 

information. 

Supplemental dehumidification. All homes in this climate call for supplemental dehumidification; the 

reduced sensible load of high-performance homes reduces the dehumidification that the AC unit provides, 

extends shoulder seasons, and raises the impact of occupant-generated moisture. 

There are a number of different ways to accomplish supplemental dehumidification with varying costs 

and performance advantages (For a detailed discussion of supplemental dehumidification, see 

http://www.buildingscience.com/resources/mechanical/conditioning_air.pdf). One low-cost yet effective 

approach and one more costly but higher performance/systems-engineered approach are described as 

follows: 

Ducted stand-alone dehumidifier: This system is a "site-constructed" and consists of an off-the-shelf 

standard dehumidifier ducted in the attic and controlled by a dehumidistat located in the living space. This 

arrangement of individual components has proven to be an effective and economical system for the 

production home-building setting. The installed cost ranges from approximately $350 to $550. The 

system consists of any ENERGY STAR dehumidifier that uses a blower wheel instead of a paddle fan to 

move air past the coil (dehumidifier located in attic in an insulated enclosure and ducted to living space), 

a Honeywell dehumidistat model H8808C located in living space, and a Honeywell switching relay (with 

transformer) model RA89A 1074. 

Note: The following manufacturers make ENERGY STAR-qualified blower wheel stand-alone 

dehumidifiers: 

LG Electronics 

(http://www.lge.com/catalog/prodlist?categoryId=CTG100515&modelCategoryId=CTG1000521&pa

rentId=CTG1000440) all models 

Haier America (http://www.haieramerica.com/categories.php?cat_id=2) all models 

Heat Controller (http://www.heatcontroller.com/) all BHD models use a turbo-impeller with turned 

blades. 

You can check the EPA ENERGY STAR Web site for dehumifiers from these manufacturers 

(http://www.energystar.gov/index.cfm?c=dehumid.pr_dehumidifiers). 

Aprilaire 1700. This is a truly engineered, coherently manufactured, supplemental dehumidification 

system with built-in air filtration, ducted design, and a controls package that integrates central-blower 

cycling for distribution, dehumidification, and intermittent introduction of outside air ventilation. The 

system is also designed for flexibility; it can be connected to the conditioned space directly or to the 

central air-distribution system in a number of configurations. It's also compact and lightweight enough to 

be set on or hung from most framing. The product cost for this system is currently about $1,100. For more 

information, see http://www.aprilaire.com/category.asp?id=F63D255EB0054BBF811DBB024BF068FA. 

For more information on other high performance supplemental dehumidification systems, see 

http://www.thermastor.com/DesktopDefault.aspx. 
 

1-30

Ducts in conditioned space. The preferred method for keeping HVAC ducts and mechanical equipment 

inside conditioned space is moving them down from the attic. In this building profile, a conditioned attic 

can be used for HVAC ducts and equipment. In no case should HVAC ducts be placed within exterior 

wall assemblies―this is not part of what is meant by ducts in conditioned space. A vented attic assembly 

may be used in this climate as long as the ceiling plane is airtight and no ductwork or air-handling 

equipment is located in the attic. 

Transfer grilles. Single air returns require transfer grilles to provide return pathways that prevent 

pressurization of bedrooms. Appropriate sizing for ducts, including these pressure relief methods, can be 

found in the Cooling System Sizing Pro

(http://www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf). 

Water heater. Any type of gas water heater (in terms of venting) works if the water heater is located in 

the garage. If the water heater is located inside conditioned space, then it must be a gas power vented or 

power-direct vented unit or an electric water heater. 

Field Experience Notes 

Air Sealing and Caulking of Panel Joints 

An increase in moisture content can occur as a result of air leakage through SIP panel joints. Airtransported moisture will migrate to the cold side of the panel causing the cold side of the panel to expand 

relative to the warm side. See Figure 1-16 for recommended air-sealing locations between panels. 

Roofing 

Light-colored standing-seam metal roofs yield the best cooling load reduction of any roof claddings. We 

recommend a metal roof that meets the EPA/DOE ENERGY STAR qualifications 

(http://128.121.47.106/index.cfm). 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow highperformance start-up procedures. 

Material Compatibility and Substitutions 

Exterior Sheathing / Building "Paper" 

A variety of building papers or housewraps installed shingle fashion can act as the drainage plane in this 

assembly. While drying to the exterior is not the primary mechanism in this climate, the combinations of 

building papers and exterior sheathings in this assembly (and their relative permeabilities) promote 

intermittent drying in this direction. 

Flooring 

Many finished flooring materials — either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example) — should only be installed over a slab with a 

low w/c ratio (≈ 0.45 or less) or a slab allowed to dry (<0.3 grams/24hrs/ft2) prior to installation of 

flooring. In general, sheet vinyl flooring should be avoided. 

Sub-slab Sand Layers 

A sand layer under the slab (to prevent differential drying and cracking) should never be placed between a 

vapor barrier and a concrete slab. Cast the concrete directly on top of the vapor barrier. This problem is 
 

1-31

better handled with a low w/c ratio (≈ 0.45 or less) and wetted burlap covering during initial curing (see

Appendix C). 

Latex Paint 

The substitution of low permeability finishes (vinyl wall paper, oil-based paints) for latex paint is strongly 

discouraged because of reduced drying potential. (Note that there are latex paints with very low vapor 

permeabilities, but they are generally clearly labeled as such.) 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, laundry rooms, and kitchens are excellent 

candidates for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s 

DensArmor®, USG’s Fiberock®). In addition, paper-faced gypsum board should never be used as 

interior sheathing or backer for tub or shower surrounds where ceramic tile or marble (any material with 

joints or grout lines) is used as the finish. 
 

1-32

Building Profile #4. The Montgomery 

Foundation: Conditioned crawl Attic: Unconditioned Cladding: Vinyl or aluminum siding 

Above Grade Wall: Wood frame Roof: Standing seam metal roof 

Figure 1-19. Cross Section of the Montgomery 
 

1-33

Building Science Details

Conditioned Crawlspace 

Conditioning of the crawlspace means that this space must be constructed much like a living space—it 

must be supplied by the HVAC system and have a transfer grille to return air back to the HVAC system 

located in the living space. The supply air should be directed horizontally across the crawlspace with 

good enough “throw” to provide some mixing, not directed down at the floor. Sizing of the supply air 

flow should be based on about 5% of the conditioned crawlspace floor area (for example: 0.05 

cfm/ft2

*1,600ft2 = 80 cfm for a 1,600 ft2 conditioned crawlspace). A single 6-in.-diameter supply duct 

typically suffices. Transfer air should go back to the central area of the living space above the crawlspace. 

Two grilles (10 in. by 4 in.) on opposite sides of the crawlspace are usually sufficient. The transfer area 

should be calculated in the same manner as for closed bedrooms connecting to hallways, using the 3-Pa 

pressure difference limit. Some form of mechanical moisture control for the crawlspace is necessary. We 

recommend one of the following approaches: 

1. Controlled ventilation strategy using the intermittent central fan-integrated supply—it provides 

both mixing and moisture removal for the crawlspace as well as the house 

2. A stand-alone dehumidifier installed in the crawlspace 

3. A continuously operating crawlspace exhaust fan with make-up air extracted from the house. 

In the Montgomery, the rigid insulation is applied to the interior face of the exterior foundation walls. 

Moisture control is important to proper performance, in particular the vapor barrier ground cover on the 

floor of the crawlspace. The vapor barrier must be continuous and sealed to the perimeter wall and any 

supporting piers. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists, 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draftstopping material (wood blocking) and 

sealant/caulk, or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the 

air barrier. The air barrier detail on second-story band joists is important because it is inaccessible 

(covered by structural/finish floor and ceiling finish) after construction. The air barrier/thermal envelope 

detail is important on ground floor band joists because of the thermal bridge that can occur at the top of 

crawlspace foundation walls (as the result of the air barrier and thermal envelope moving from the outside 

to the inside of the building envelope and termite inspection zones located at the top of crawlspace 

foundation walls). Note that while fiberglass batts fulfill the requirement for protection from ignition in 

the open band joists, fiberglass batt material by itself cannot maintain the air barrier. 

Attached Garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 1-20 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. Refer to www.buildingscience.com/housesthatwork/airsealing/default.htm for air-sealing details.
 

1-34

Figure 1-20. Creating a continuous air barrier 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information (www.buildingscience.com/resources).

This wall assembly permits drying to both the interior and the exterior (depending on the selection of 

exterior sheathing―see Material Compatibility and Substitutions). The roof assembly is designed to dry 

only to the interior (without continuous back-venting of the impermeable metal roof, little if any drying 

can take place to the exterior). 

Drainage Plane, Air Barrier, and Vapor Control 

This wall assembly is a screen system—the vinyl siding promotes air movement through all laps; the 

drainage plane is the lapped building paper or housewrap installed over the exterior sheathing. 

Alternatively, the exterior surface of the Thermo-ply® sheathing applied “shingle fashion” acts as the 

drainage plane. The roofing paper underneath the standing seam metal roof has two functions. It serves as 

a slip surface for the roofing for expansion and contraction of the metal, and it serves as a secondary 

drainage plane for moisture that might condense on the underside of the metal roofing as the result of 

night-sky radiation and subsequent condensation. Note that the OSB roof deck has the capacity to act as a 

hygric buffer and store moisture. 

Thermal Barrier 

In this climate, moisture control does not require specific levels of insulation. Inside/outside temperature 

differences do not require any cavity-warming exterior rigid insulation to control wintertime condensing 

surface temperatures. Having said this, insulating sheathing in general is a good idea. We recommend full 

cavity fill in the walls, but the 2-x-6 framing is more about advanced framing than the depth of cavity 

insulation that can be achieved. 

Window Flashing 

Window flashing details are wall assembly or cladding specific (Figure 1-21 and refer to the EEBA Water 

Management Guide available at www.eeba.org/bookstore. 
 

1-35

Advanced Framing 

An important element of high performance wood-frame construction is an advanced framing package, in 

this case including cross bracing for shear resistance. For more detailed information on advanced framing 

techniques, see www.buildingscience.com/housesthatwork/advancedframing/default.htm. 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The crawlspace to roof vent system handles conditions that are difficult if not impossible to assess before 

completion of the structure—resultant confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this "ounce" of prevention is well balanced against the 

cost of the "pound" of cure. A conditioned crawlspace only heightens the importance of soil gas 

ventilation. Note that this system is a passive system, but it can easily be converted to an active 

ventilation system by installing an in-line fan into the stack in the attic. 

Sub-Slab Stone Bed 

The 4-in.-deep 3⁄4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. The sub-slab stone bed is a practical method 

for venting soil gas should it be necessary. 

Figure 1-21. Window flashing 
 

1-36

Crawlspace Access 

The preferred location for crawlspace access is through the subfloor; any access through the perimeter 

wall must be air-sealed and insulated. 

Climate-Specific Details 

Termite Management 

In hot-humid climates, termites are best managed with a three-pronged approach that deals with the three 

things termites need―cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain the 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor by the others. For example, if for some reason chemical treatment of 

soil or building materials is not an option, then complete rigor in controlling moisture and ground cover 

must be maintained. 

Mechanical Systems 

The following are key elements of a system for this climate: 

Sealed-combustion gas furnace. This provides energy efficiency and health/safety with the unit inside 

conditioned space. 

Minimum 12 SEER A/C unit. This air-conditioning unit provides energy efficient management of 

sensible load. 

Central-fan-integrated supply ventilation. This system is simple, effective, and economical. It provides 

fresh, filtered, outside air in a controlled amount using the existing HVAC delivery system for even 

distribution and mixing. Set-up intermittent central-fan-integrated supply, designed to ASHRAE 62.2P 

rate, with fan cycling control set to operate the central air handler 20 minutes every hour to provide 

ventilation air distribution and whole-house averaging of air quality and comfort conditions ($125 to 

$150). Include a normally closed motorized damper in the outside air duct with the AirCyclerTM FRV 

control (+$50 to $60). See www.buildingscience.com/resources/mechanical/air_distribution.pdf for more 

detailed information. 

Supplemental dehumidification. All homes in this climate call for supplemental dehumidification 

because the reduced sensible load of high performance homes reduces the dehumidification the A/C unit 

provides, extends shoulder seasons, and raises the impact of occupant-generated moisture. The ducted 

stand-alone dehumidifier in the attic controlled by a humidistat located in the living space has proven to 

be the most effective and economical system for the production home building setting. Our recommended 

system (+$300 to $350) includes GE dehumidifier model AHG40FCG1 located in an insulated enclosure 

in the attic and ducted to living space, Honeywell humidistat model H8808C located in the living space, 

and Honeywell switching relay (with transformer) model RA89A 1074. For a detailed discussion of 

supplemental dehumidification see www.buildingscience.com/resources/mechanical/conditioning_air.pdf.
 

1-37

Ducts in Conditioned Space 

The preferred method for keeping HVAC ducts and mechanical equipment inside conditioned space is to 

keep them in the living space. Moving the conditioned boundary down so that the crawlspace is 

conditioned works as well, as shown in Figure 1-22. The crawlspace must be conditioned (with the air 

barrier and thermal barrier following the foundation) so that the crawlspace does not become a potentially 

large moisture trap. In no case should HVAC ducts be placed within exterior wall assemblies―this is not 

what is meant by ducts in conditioned space. 

Alternatively, if ducts must be located in the attic, the conditioned boundary must be moved up to the 

underside of the roof sheathing so that the attic is conditioned. 

Transfer Grilles and Jump Ducts 

Single central air returns require transfer grilles to provide return pathways that prevent pressurization of 

bedrooms. Appropriate sizing and placement of these pressure relief methods, can be seen in Figure 1-23 

with additional details at 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

 

Figure 1-22. Mechanical system and ventilation in conditioned crawlspace 
 

1-38

Figure 1-23. Transfer grilles and jump ducts 

Water Heater 

Any type of gas water heater (in terms of venting) is adequate if the water heater is located in the garage. 

If the water heater is located inside conditioned space, then it must be a gas power vented or power-direct 

vented unit, or an electric water heater. 

Field Experience Notes 

Air Sealing 

Unvented assemblies—walls or roofs—are robust when the air sealing is robust. The hardest spots are not 

the "fields" but the "margins" of assemblies. Spray foam applied at the margins (truss/rafter end blocking) 

may seem like an expensive element of the assembly, but the labor savings and air sealing quality in 

comparison to the alternatives make it a good choice. 

Roofing 

Light-colored standing seam metal roofs yield the best cooling load reduction of any roof claddings, 

which is important in this climate. We recommend a metal roof that meets the EPA/DOE ENERGY 

STAR qualifications: 208.254.22.7/index.cfm?c=roof_prods.pr_crit_roof_products. 

Flashing Details 

Because the vinyl siding is a screened wall cladding system, flashing details should be accomplished in 

the plane of the drainage plane (building paper or house wrap), not the cladding. Do not caulk siding and 
 

1-39

do not rely on "J"-channels as part of the drainage plane. (In other words, never consider vinyl siding, 

aluminum siding, or any siding for that matter, as the weather barrier). 

Termite Inspection Gap 

Our experience has shown that building inspectors will accept a 1- to 2-in. (rather than a 6-in.) termite 

inspection gap. This reduces the extent of uninsulated concrete and, therefore, reduces the associated heat 

loss. 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/1619_Yost&Edminster_for_au.pdf.

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 1-24 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss. 

Conditioned Crawlspaces 

This assembly may require some local building code official "building science persuasion." See the 

Building Safety Journal article written by Nathan Yost of BSC:

www.buildingscience.com/resources/articles/24-27_Yost_for_author.pdf.

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow high 

performance start-up procedures such as the following: 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf. 

Figure 1-24. Energy truss, also known as a “slider truss” 
 

1-40

Material Compatibility and Substitutions 

Exterior Sheathing/Building “Paper” 

A variety of building papers or housewraps installed shingle fashion can act as the drainage plane in this 

assembly. While drying to the exterior is not the primary mechanism in this climate, the combinations of 

building papers and exterior sheathings in this assembly (and their relative permeabilities) promote 

intermittent drying in this direction. Note that OSB is more vapor permeable than XPS insulation, which 

is more vapor permeable then Thermo-Ply® (see Table 1, Building Material Properties). 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). This permits drying to both the interior and exterior in this wall assembly. 

Note that when foam insulation is left exposed in an assembly, a "thermal barrier" or "protection against 

ignition" may be required. Code implementation/interpretation has proven to be particularly troublesome 

for "gray" areas, such as spaces that are conditioned but not occupied (conditioned attics and 

crawlspaces). 

Cast Concrete Foundation Walls 

If block is used instead of cast concrete for foundation walls, the bond beam becomes essential to 

maintain air barrier continuity at the top of the block wall. 

Crawlspace Floor 

Ideally, the crawlspace floor would be a 4-in. gravel (free-draining, no fines) bed, polyethylene sheeting 

layer, and "rat" (2-in. low-strength cast concrete) slab, making this space more amenable to light storage 

and housing of HVAC equipment. The cost of this approach may outweigh the benefits for builders and 

buyers. If a concrete slab is cast, it should be placed directly on top of the vapor barrier. 

Wall Sheathing 

Moisture drive in a hot-humid climate is predominantly from the outside in. Select the wall sheathing and 

building paper combination to maintain functions of drainage plane and shear resistance and relatively 

low vapor permeability. Consult the Building Materials Property Table (Table 1). 

Latex Paint 

The substitution of low permeability finishes (vinyl wall paper, oil-based paints) for latex paint is strongly 

discouraged because of reduced drying potential. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, laundry rooms, kitchens, are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 
1-41 

Table 1. Building Materials Property Table 

HPR = Hydrostatic Pressure Resistance (AATCC127)

SD = SE84)

AP = Air permeability (ASTM E2178-01) WA = W

FS = Flame Spread (ASTM E84)

VAPOR PERMEABILITY 

(Perm-in)a

MATERIAL 

TYPICAL 

RELEVANT 

DIMENSION 

REPRESENTATIVE 

WET CUP 

REPRESENTATIVE DRY 

CUP 

WATER 

ABSORPTIONc R- VALUE OTHER RELEVANT PROPERTY COMMENTS W

Exterior Sheathings Plywood (CDX) 3/8-in. 3.5 0.75 na 0.5 FS = 76-200 SD =130 At saturation, factor of 10 increase in permeability ―14 - 20.5 permsb www.ap

t = pub_

OSB 3/8-in. 2 0.75 na 0.5 FS = 148 SD = 137 At saturation, marginal increase in permeability ― 2.8 - 3.4 perms www.osFiberboard - asphalt impregnated 

7/16-in. 15 14.5 2.3 - 7% 1.2 FS > 75 AP = 0.82 among the most vapor permeable of exterior sheathings 

www.tem

e/fbrpg8

www.ca

/1_0_1_

Thin profile structural sheathing 

0.078 to 

0.137-in. 0.5 - 0.6 0.5 - 0.6 na 0.2 - 3.4 R-value dependent on air space; this sheathing is essentially an exterior vapor barrier www.sim

productsheetTP1

Foil-faced PIR insulation 1-in. 0.03 0.01 0% 7 FS = 5 SD = 165 

combined thermal, vapor transmission & combustion properties must be used appropriately 

www.pim

XPS rigid insulation 1-in. 1 1 0.10% 5 

FS = 5 SD = 165 AP = 0?

Compare/contrast moisture properties to EPS CAREFULLY 

www.do?filepath04429.p
1-42 

Table 1. Building Materials Property Table (continued) 

VAPOR PERMEABILITY 

(Perm-in)a

MATERIAL 

TYPICAL 

RELEVANT 

DIMENSION 

REPRESENTATIVE 

WET CUP 

REPRESENTATIVE DRY 

CUP 

WATER 

ABSORPTIONc R- VALUE OTHER RELEVANT PROPERTY COMMENTS W

Exterior Sheathings (continued) XPS (skinned) 3/8-in. 0? 0? 1.5 

polypro skin enables the fan-fold, but can be removed and greatly affects vapor permeability 

EPS rigid insulation (Type 1) 1-in. 5 6% 3.7 

FS = 115 SD = 430 AP = 12.2

Compare/contrast moisture properties to EPS, CAREFULLY 

www.leg

Glass mat faced gypsum board (DensGlass®) 1⁄2-in. 23 5% 0.56 FS = 0 SD = 0 among the most vapor permeable of exterior sheathings www.gp

.html

Wall Claddings Brick 3-1/2-in. 1.7 - 13.7 0.1 

Properties as variable as the material, but water storage capacity is always very high 

Traditional stucco 7/8-in. 5.8 3.8 0.1 

Properties as variable as the material, but almost always has relatively high vapor permeability 

Polymer-modified stucco 

Vapor permeability is dependent on paint, with latex pain generally in the 2-3 perm range and with elastomeric paint highly variable 

Cedar/redwood lap siding (unfinished) 3/8-in. 0.5 FS = 69 SD = 98 

www.cesiding.clications

Pine/spruce/fir lap siding (unfinished) 3/8-in. 0.4 - 5.4 0.5 Fibercement lap siding (primed all surfaces) Vinyl lap siding n/a 
1-43 

Table 1. Building Materials Property Table (continued) 

VAPOR PERMEABILITY 

(Perm-in)a

MATERIAL 

TYPICAL 

RELEVANT 

DIMENSION 

REPRESENTATIVE 

WET CUP 

REPRESENTATIVE DRY 

CUP 

WATER 

ABSORPTIONc R- VALUE OTHER RELEVANT PROPERTY COMMENTS W

Interior Wallboards Standard paper-faced 1⁄2-in. 40 FS = 15 SD = 0 

Both faces and core highly water vapor permeable; paper faces highly susceptible to mold and mildew growth 

DensArmor PlusTM 1⁄2-in. 23 12 5% FS = 10 SD = 0 

Paper facings are replaced with fiberglass mat facings for increased resistance to moisture, mold, and mildew 

www.gp

Fiberock® 1⁄2-in. Hardie Tilebacker 1⁄2-in. DensShield® 1⁄2-in. A tilebacker board with the top face acrylic coating acting as water and 

moisture barrier 

www.gp

html

Durock® 1⁄2-in. Cavity Fill Insulations Fiberglass/Rockwool (unfaced batt) 3-1/2-in. 168 120 11 FS = 10 SD = 10 The thermal performance of all batt insulation depends on independent air sealing components and details www.ow

tion/prod

Cellulose 3-1/2-in. 75 <15% 13 FS < 25 SD < 50 

Although the air tightness of cellulose insulation is significantly better than some other common cavity fill insulation, its thermal performance still depends on independent air sealing components and details 

www.usspecs.a

Modified spray urethane 3-1/2-in. 16 0% 12.6 to 14 FS < 250 SD < 400 AP = 0.008 www.icy

tionfact.
1-44 

Table 1. Building Materials Property Table (continued) 

VAPOR PERMEABILITY 

(Perm-in)a

MATERIAL 

TYPICAL 

RELEVANT 

DIMENSION 

REPRESENTATIVE 

WET CUP 

REPRESENTATIVE DRY 

CUP 

WATER 

ABSORPTIONc R- VALUE OTHER RELEVANT PROPERTY COMMENTS W

Flooring Hardwood 3⁄4-in. Softwood 3⁄4-in. Glazed tile 3/8-in. Synthetic carpet Organic fiber carpet Linoleum Vinyl tile 

essentially vapor impermeable ―not recommended with concrete floors, particularly with high w/c ratios 

Vinyl sheet 

1/32 to 1/16 

in. 

essentially vapor impermeable ―not recommended with concrete floors, particularly with high w/c ratios 

VAPOR PERMEANCE AIR PERM.

(Perms) (L/s*m2 @ 75 Pa) 

Building Papers 15# asphalt roofing paper 6 (dry cup) - 31 (wet cup) 0.4 vapor permeable at any moisture content 30# asphalt roofing paper 0.19 Tyvek® 58 (wet cup) 0.0045* HPR = 210 cm (@ wind pressure 30 mph, NOT 75 Pa) www.tyv

products

Typar® 0.013" 14 (dry cup) 0.0023 HPR = 165 cm FortiFiber® Jumbo Tex®
1-45 

Table 1. Building Materials Property Table (continued) 

MATERIAL 

TYPICAL 

RELEVANT 

DIMENSION 

OTHER 

RELEVANT 

PROPERTY 

COMMENTS W

VAPOR PERMEANCE AIR PERM.

(Perms) (L/s*m2 @ 75 Pa) 

Building Papers Polyethylene 0.006" (6 mils) 0.03 0? a vapor barrier appropriate only for severe cold climates MemBrainTM 2-mil 1 (dry cup) - 10+ (wet cup) well-suited as a vapor pressure boundary for cold and mixed climates www.ce

dex.htmindex.ht

Coatings Vapor retarder primer 0.25 mm 0.5 Latex paint (primer+sealer) 3.5 - 6.1 Exterior acrylic paint 5.5 Semi-glosss vinyl acrylic enamel 6.6 Exterior oil-based paint (3 coats) 0.3 - 1.0 Oil paint (1 coat+primer) 1.6 - 3 Elastomeric paint 

lots of variability in water vapor permeability 

www.ma

a The water vapor permeability of a material is roughly inversely proportional to its thickness—doubling the thickness halves the permeabilit

films and coatings, however, and this rule should not be applied to these materials. 

b Building Science Consortium definition: a perm is a unit of measurement that reflects how readily water vapor passes through a material of 

with a perm rating less than 1 is considered impermeable, greater than 1 but less than 10 perms is considered vapor semi-permeable, and grea

considered vapor permeable.

c Although manufacturers often report this property per ASTM C209 and as a per cent by weight, this only gives information about the mater

quantity of water absorbed over an indefinite―long, often 24 hours―time period) and what is much more useful is the material's water absoWICKING (initial rate of capillary transport). There is unfortunately NO relationship between the two, no ASTM standard for the water abso

manufacturers in North America have measured or reported water absorption coefficients. When researching a building product, strongly encPROVIDE the water absorption coefficient. 
 

2-1

II. Houses That Work for Cold Climates 

Introduction 

For the purpose of this report, a cold climate is considered a region with approximately 5,400 heating 

degree days or more, but fewer than 9,000 heating degree days. In North America, most cold climates 

vary in annual precipitation from less than 20 in. to more than 60 in. Condensation of warm interior air on 

cold surfaces within the building assembly is a concern in design and construction. In addition, in many 

areas ground water presents a concern because most houses are built with basements or crawl spaces. 

Rain, snow, and ice damming represent threats to the integrity of the building envelope. Until recently, 

the focus in terms of moisture control in cold climates was moisture drive from the interior during the 

heating season. The widespread introduction of centralized cooling in cold climates, however, can 

produce cold interior surfaces on which warm moist air infiltrating from the exterior can condense during 

the summer. If interior vapor barriers are installed in conjunction with air conditioning, serious moisture 

problems can occur. Interior vapor barriers should be avoided in this climate region. Note that there is a 

difference between an interior vapor barrier and interior vapor retarder (see “Insulations, Sheathings and 

Vapor Diffusion Retarders” at www.buildingscience.com/resources). Controlling moisture and air flow in the 

building envelope in this climate is critical to designing and building a durable, comfortable home. 

We have chosen three Building Profiles that represent different regional building practices in cold 

climates: 

• The “Chicago”—two-story, stick-framed, basement, first- and second-floor vinyl siding, vented 

attic, asphalt shingle roof (Figure 2-1) 

• The “Denver”—two-story, stick-framed, basement with sub-crawl, stucco, vented cathedral 

ceiling, asphalt shingle roof (Figure 2-6) 

• The “Minneapolis”—one-and-a-half-story, stick-framed, slab-on-grade, stucco, vented cathedral 

ceiling, asphalt shingle roof (Figure 2-12). 

A substantial amount of repetition is present in these Building Profiles, but is necessary in order to 

provide comprehensive, stand-alone, examples of performance packages that achieve 40% energy savings 

while maintaining or improving quality and durability. 

For information about a production builder from this climate, see 

www.buildingscience.com/buildingamerica/casestudies/prairie_crossing.htm. This case study explores the 

builder's experience with the BA program and discusses the reasons for the specific design and 

construction details that were used at Prairie Crossing. For an additional case study of a green townhouse 

infill project in Cleveland, Ohio, see www.buildingscience.com/buildingamerica/casestudies/ecovillage.htm. To 

see the detailed drawings on Advanced Framing and Air Sealing Techniques, go to 

www.buildingscience.com/housesthatwork. Additional information on construction methods and alternative 

designs is available in the EEBA Builder's Guide for Cold Climates. 
 

2-2

Building America Best Practices for Cold Climates 

High-performance Building America homes in cold climates must cope with substantial moisture drive 

from the building interior and into the building envelope during the heating season, as well as ground 

water and moisture issues given that full basements and crawlspace basements dominate within this 

climate zone. Many, if not most, high-performance production homes within this climate zone are being 

equipped with central forced-air conditioning systems, introducing yet another moisture stress that 

requires control in the design and outfitting of the envelope and HVAC system. 

The following Best Practices have been compiled primarily from two BSC resources: the Building 

America Performance Targets (www.buildingscience.com/buildingamerica/targets.htm) and the Cold 

Climate Building Profiles, the “Denver,” the “Chicago,” and the “Minneapolis.” All climate-specific Best 

Practices are identified with a bolded and bracketed [C]. 

Process: Building Design, Systems Engineering, and Commissioning 

Design for Energy Performance 

Energy performance for space conditioning and hot water is 40% better than the 1995 Model Energy 

Code base case house (i.e., 10% better than ENERGY STAR® performance requirements). 

Systems Engineering 

Design structure using advanced framing methods (see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm or 

www.buildingscience.com/resources/presentations/advanced_framing.pdf). 

Design structure to accommodate the most efficient duct distribution system that places all ducts and air 

handling equipment within conditioned space (see 

www.buildingscience.com/resources/misc/wood_efficiency.pdf, specifically Figure 3 and page 5). 

Design and detail structure for durability, in terms of wall and roof assembly drying potential, continuous 

drainage plane, and continuous thermal barrier that clearly defines the conditioned space (See Building 

Profiles). [C]

Commissioning – Performance Testing 

Air leakage (determined by blower door depressurization testing) should be less than 2.5 in.2/100 ft2

surface area leakage ratio (CGSB [Canadian General Standards Board], calculated at a 10-Pa pressure 

differential); or 1.25-in.2

/100 ft2 leakage ratio (ASTM, calculated at a 4-Pa pressure differential); or 0.25 

cfm/ft2

 of building envelope surface area at a 50-Pa air pressure differential. If the house is divided into 

multiple conditioned zones, such as a conditioned attic or conditioned crawl space, the blower door 

requirement must be met with access to the space open, connecting the zones. 

Ductwork leakage to the exterior for ducts distributing conditioned air should be limited to 5% of the total 

air handling system rated air flow at high speed (nominal 400 cfm per ton) determined by pressurization 

testing at 25 Pa. Two acceptable compliance mechanisms are (1) test duct leakage to outside at finish 

stage or (2) test total duct leakage at duct rough-in stage. 

Forced-air systems that distribute air for heating and cooling should be designed to supply airflow to all 

conditioned spaces and zones (bedrooms, hallways, basements), as well as to provide a return path from 

all conditioned spaces or zones. Interzonal air pressure differences, when doors are closed, should be 

limited to 3 Pa. This is typically achieved by installing properly sized transfer grilles or jump ducts (see 

www.buildingscience.com/resources/mechanical/transfer_grille_detail.pdf and 

www.buildingscience.com/resources/mechanical/transfer_grille_sizing_charts.pdf). 

Mechanical ventilation system airflow should be tested during building commissioning. 
 

2-3

Testing of the house should be completed as part of the commissioning process. The SNAPSHOT form 

is available for download as a convenient way to record the testing information (see 

www.buildingscience.com/buildingamerica/snapshot_form.pdf). Instructions for completing the form are 

also available (see www.buildingscience.com/buildingamerica/snapshot_instructions.pdf). Unique or 

custom house plans should each be tested. In production settings, each model type (i.e., floor plan) should 

be tested until two consecutive houses of this model type meet testing requirements. Then, testing on this 

model type can be reduced to a sampling rate of one in seven (i.e., one test, with six "referenced" houses). 

Small additions to a floor plan (e.g., bay window, conversion of den to bedroom) should be considered 

the same model type; major changes (e.g., bonus room over the garage, conversion of garage into a hobby 

room, etc) should be considered a separate model type. 

Site: Drainage, Pest Control, and Landscaping 

Drainage 

Grading and landscaping shall be planned for movement of building run-off away from the home and its 

foundation, with roof drainage directed at least 3 ft beyond the building, and a surface grade of at least 

5% maintained for at least 10 ft around and away from the entire structure. 

Pest Control 

Based on local code and Termite Infestation Probability (TIP) maps, use environmentally appropriate 

termite treatments, bait systems, and treated building materials that are near or have ground contact (See 

www.uky.edu/Agriculture/Entomology/entfacts/). [C] 

Landscaping 

Plantings should be held back as much as 3 ft and no less than 18 in. from the finished structure, with any 

supporting irrigation directed away from the finished structure. Decorative ground cover—mulch or pea 

stone, for example—should be thinned to no more than 2 in. for the first 18 in. from the finished structure 

(See Building Profiles). [C] 

Foundation: Moisture Control and Energy Performance 

Moisture Control 

The building foundation shall be designed and constructed to prevent the entry of moisture and other soil 

gases. (See Building Profiles). [C]

Semi-permeable rigid insulation should be used as both a thermal layer and vapor control beneath the 

slab—a 6-mil poly vapor barrier is required if rigid insulation is not used here. Use either rigid insulation 

or poly, not both. [C] 

Sub-slab drainage shall consist of a granular capillary break directly beneath the slab vapor barrier. 

Perimeter drainage should be used per the Building Profiles – Cold Climates. [C] 

Use radon resistant construction practices as described on the EPA radon control web site 

(www.epa.gov/iaq/radon/construc.html). 

Energy Performance 

A basement insulation system (type of insulation, location, thermal/air sealing/vapor permeability 

properties/fire rating) that controls the flow of heat and moisture is required for this climate. A number of 

different approaches will work; a number will not (see Building Profiles and 

www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf). [C] 
 

2-4

Envelope: Moisture Control and Energy Performance 

Moisture Control 

Water management. Roof and wall assemblies must contain elements that provide drainage in a 

continuous manner over the entire surface area of the building enclosure, including lapped flashing 

systems at all penetrations. See the Building Profiles or the EEBA Water Management Guide for specific 

details for various wall assemblies. [C] 

Vapor management. Roof and wall assemblies must contain elements that, individually and in 

combination, permit drying of interstitial spaces. In this climate, control of the first condensing surface by 

boosting the thermal resistance of exterior sheathing is an important element of high performance 

construction. See Building Profiles. [C]

Energy Performance 

Air leakage. Exterior airflow retarder (foam sheathing) or interior air-flow retarder (gypsum board) is 

sealed to the slab and frame walls (Airtight Drywall Approach [ADA]). For details of the ADA for 

interior airflow retarders, see the Building Profiles. [C]

Windows. One of two approaches is recommended: 

• U-factor 0.35 or lower and SHGC (solar heat gain coefficient) 0.35 or less, regardless of climate 

• Climate and/or orientation-specific glazing properties if the builder can employ passive solar 

orientation and design, and occupants can be expected to operate window shading in concert with 

time of day and weather conditions. [C]

Mechanicals / Electrical / Plumbing 

Systems Engineering

HVAC system design, both equipment and duct, should be done as an integral part of the architectural 

design process.

HVAC system sizing should follow ACCA Manual J and duct sizing should follow ACCA Manual D (see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf)

Mechanical ventilation should be an integral part of the HVAC system design (see Figure 13 in 

www.buildingscience.com/housesthatwork/cold/default.htm and 

www.buildingscience.com/resources/mechanical/advanced_space_conditioning.pdf.) [C] 

Energy Performance

Air conditioner or heat pump shall be installed according to best practices (see 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf).

Major appliances meet high-energy efficiency standards using current appliance ratings. Only those 

appliances in the top one-third of the DOE Energy Guide rating scale should be selected. For further 

details, see www.eren.doe.gov/consumerinfo/energy_savers/appliances.html and “Using Wood 

Efficiently” at www.buildingscience.com/resources/misc/wood_efficiency.pdf.

Occupant Health and Safety

Base-rate ventilation. Controlled mechanical ventilation per ASHRAE Standard 62.2. 

Spot ventilation. Intermittent spot ventilation of 100 cfm should be provided for each kitchen; all kitchen 

range hoods must be vented to the outside (no recirculating hoods). Intermittent spot ventilation of 50 cfm 

or continuous ventilation of 20 cfm when the building is occupied should be provided for each 

washroom/bathroom.
 

2-5

All combustion appliances in the conditioned space must be sealed combustion or power vented. 

Specifically, any furnace inside conditioned space should be a sealed-combustion 90%+ unit. Any water 

heater inside conditioned space should be power vented or power-direct vented. Designs that incorporate 

passive combustion air supply openings or outdoor supply air ducts not directly connected to the 

appliance should be avoided.

Provide filtration systems for forced-air systems that provide a minimum atmospheric dust spot efficiency 

of 30% or MERV (Minimum Efficiency Reporting Value) of 6 or higher.

Indoor humidity should be maintained in the range of 25 to 60% by controlled mechanical ventilation, 

mechanical cooling, or dehumidification. (See 

www.buildingscience.com/resources/moisture/relative_humidity_0402.pdf.)

Carbon monoxide detectors (hard-wired units) shall be installed (at one per every approximate 1,000 ft2

) 

in any house containing combustion appliances and/or an attached garage.

Information relating to the safe, healthy, comfortable operation and maintenance of the building and 

systems that provide control over space conditioning, hot water, or lighting energy use shall be provided 

to occupants.

Envelope/Mechanicals Management 

Plumbing. No plumbing in exterior walls. Air seal around plumbing penetrations in pressure boundary 

(air barrier) such as rim (band) joist or ceiling. 

Electrical. Seal around wires penetrating air barrier or pressure boundary.
 

2-6

Building Profile #5. The Chicago 

Foundation: Basement Attic: Unconditioned Cladding: Vinyl siding 

Above Grade Walls: Wood frame Roof: Asphalt shingles 

Figure 2-1. Cross section of the Chicago
 

2-7

Building Science Details 

Ducts in Conditioned Space 

The Chicago (Figure 2-1) is designed to accommodate HVAC equipment and ducts in the basement and 

living space, not in an unconditioned attic. HVAC ducts should not be run in exterior walls. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draftstopping material (wood blocking) and 

sealant/caulk, or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the 

air barrier. The air barrier detail on second-story band joists is important because it is inaccessible 

(covered by structural/finish floor and ceiling finish) after construction. Note that while fiberglass batts 

fulfill the requirement for protection from ignition in the open band joists, fiberglass batt material by itself 

cannot maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 2-2 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. See also www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Figure 2-2. Air sealing and an attached garage. 
 

2-8

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls/insulation_sheathing.pdf). 

In cold climates, the moisture load in the winter months is primarily from the interior, so roof and wall 

assemblies are generally designed to dry primarily to the exterior. Wintertime condensation control can be 

facilitated by elevating the temperature of the first condensing surface (the outside of the exterior 

sheathing) via the use of insulating sheathing. When XPS (with relatively low permeability) is used, then 

only slow drying is available to the exterior. Accordingly, most drying occurs to the interior during the 

summer months. Therefore, interior vapor barriers should not be installed. Note that there is a difference 

between an interior vapor barrier and an interior vapor retarder. Particular care must be taken to prevent 

the entry of bulk water (i.e., leaks) and to control interior relative humidity in the coldest months (see 

Material Compatibility and Substitutions). 

Drainage Plane, Air Barrier, Vapor Control 

This wall assembly is a screen system—the vinyl siding promotes air movement through all laps; the 

drainage plane is the lapped building paper or housewrap installed over the exterior sheathing. Note how 

flashing maintains the continuity of the drainage plane at transitions. Continuity of the drainage plane on 

gable end walls framed over stud walls with exterior insulating sheathing can be accomplished as shown 

in Figure 2-2. 

This building profile has a continuous air barrier on the interior (Airtight Drywall Approach on ceiling 

and walls (see www.buildingscience.com/housesthatwork/airsealing/default.htm) and on the exterior walls (the 

sealed rigid insulation). 

In cold climates, walls are generally designed to dry to the exterior, with the exterior of the wall being 

five times more vapor permeable than the interior, or they are designed with insulating sheathing in order 

to control the temperature of the condensing surfaces. The thickness of the insulating sheathing is 

determined by calculation based on the severity of the climate (see “Insulations, Sheathings and Vapor 

Diffusion Retarders” at (www.buildingscience.com/resources/walls/insulation_sheathing.pdf). Walls constructed 

with insulating sheathing are designed to dry to the interior during the summer months. Latex paint or 

some other vapor retarder (i.e., the kraft facing on fiberglass batts or CertainTeed’s MemBrainTM Smart 

Vapor Retarder) acts to slow moisture entry into the framed assembly from the interior during the winter. 

Ideally, the more vapor permeable EPS rigid insulation works well as the thickness of insulation goes 

beyond 1 in. (see Field Experience Notes for more discussion). 

Rough Opening Flashing 

Flashing must be installed at the plane of the XPS rigid insulation for drainage plane continuity (Figure 2-

2). For more details see the EEBA Water Management Guide at www.eeba.org/bookstore. 

Advanced Framing 

This advanced framing wall assembly replaces structural sheathing with cross bracing or some alternative 

for shear resistance. Thermal performance and reduced drywall cracking are additional benefits of a 

comprehensive approach. See www.buildingscience.com/housesthatwork/advancedframing/default.htm

for details. 
 

2-9

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains the same wall height). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult if not impossible to assess before 

completion of the structure—resultant confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-Slab Stone Bed 

The 4-in.-deep, 3⁄4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 

practical, and the only capillary break between the slab and ground is the polyethylene vapor barrier or 

the rigid insulation under the slab. 

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate, where the average monthly 

temperature for the coldest month of the year goes below 45°F. The heat loss through the basement walls 

is significant enough to warrant 1-1/2 to 2 in. of rigid insulation. Note that the insulation must either 

comply with local codes for protection against ignition or be covered with material such as gypsum 

wallboard. See the BSC article on basement insulation systems at 

www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf.

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled when relative humidity 

is often the condition that requires higher ventilation rates. They can also depressurize the house causing 

loss of conditioned air. Generally, the area of the gable and soffit vents combined with the leakage of the 

attic ceiling is such that the fan pulls air not just from the exterior vent, but also from the conditioned 

space below. 
 

2-10

Climate-Specific Details 

Below-Grade Insulation 

Ground temperatures make foundation wall and slab insulation an important part of the thermal barrier. 

Above-Grade Insulation 

Homes in this climate benefit from exterior insulation that warms whatever structural material is to its 

interior, protecting it from the moisture degradation that can occur as the result of condensation. 

Ice Dam Protection 

The combination of adequate insulation just above the exterior wall and air sealing at the wall-roof 

assemblies transition is essential to prevent ice dams. But ice dams can occur even in properly detailed 

roof assemblies from differential solar snow melt. A water protection membrane at the eave is 

recommended on all roof assemblies in this climate, along with continuous soffit ventilation where a 

vented attic design is used. 

Mechanical Systems 

Heating and Cooling. A sealed combustion hot air furnace and SEER 12 air conditioning unit is 

recommended. A single central return requires transfer grilles to provide return path and avoid 

pressurizing bedrooms (Figure 2-3). 

Figure 2-3. Transfer grille and jump duct approaches 
 

2-11

Ventilation. For homes with central forced-air distribution systems, we recommend an 

intermittent central-fan-integrated supply, designed to provide the ASHRAE 62.2P 

recommended rate, with fan cycling control set to operate the central air handler 20 minutes 

every hour to provide ventilation air distribution and whole-house averaging of air quality and 

comfort conditions ($125 to $150). Outside air fraction should be designed to keep mixed air 

temperature at furnace heat exchanger above 50°F, usually not more than a 10%. Include a 

normally closed motorized damper in the outside air duct (+$50 to $60) (Figure 2-4) 

Basement Configuration 

Figure 2-4. Recommended ventilation system in the “Chicago” 
 

2-12

In “Severe Cold” climates and where flows result in lower than 50°F mixed air temperatures, ventilation 

can be accomplished using a continuous exhaust system (see next section “For homes without central 

forced air distribution”), a heat-recovery ventilator (HRV), or an energy-recovery ventilator (ERV). HRV 

or ERV systems should not be hard-connected to the HVAC system. 

For homes without central forced-air distribution system, we recommend a continuous multi-point 

exhaust, designed to provide the ASHRAE 62.2P recommended flow rate, pulling from each bedroom 

(unless the bedroom has a bathroom, in which case it will pull from the bathroom), and pulling from at 

least one location in the principal living area. A fan-cycling control for the central air handler provides 

mixing only. Any combustion appliances must be power-direct vented sealed combustion. 

Water heater. Any type of gas water heater (in terms of venting) is adequate if the water heater is 

located in the garage. If the water heater is located inside conditioned space, then it must be a gas power 

vented or power-direct vented unit, or an electric water heater. 

Insect Management 

In cold climates, insect pressure (termites and carpenter ants) is less pronounced than in warmer climates, 

but important nonetheless. A three-pronged approach deals with the three things insects need—cover, 

moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the foundation. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate building materials treatment (such as BoraCare®) for insect-prone, near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if for some reason, chemical treatment 

of soil or building materials is not an option, then complete rigor in moisture control and ground cover is 

required. 

Field Experience Notes 

Selection of Rigid Insulation 

Most builders select rigid insulation based on costs and handling properties. Although the vapor 

permeability of both EPS and rigid fiberglass insulation can make them particularly well suited to cold 

climate envelope assemblies, their lack of availability and user-friendliness generally make XPS 

insulation the builder choice. For these reasons, we recommend 1-in. or thicker XPS in most wall 

assemblies. But remember, the type of sheathing to use is always a question that should be asked in the 

context of the given cladding and the level of control that can be expected over interior relative humidity 

via mechanical ventilation. See “Insulations, Sheathings, and Vapor Diffusion Retarders” for more 

information (www.buildingscience.com/resources). 

Joint Treatment in Rigid Insulation 

Shiplapped rigid foam insulation has proven to be available in only very limited areas. Mastic works as a 

water sealant, but its long-term performance is not known (although it appears promising). Flexible 

flashing with polyethylene film is straightforward and creates a natural weatherlap and, therefore, is the 

preferred approach. 
 

2-13

Flashing Details 

Because the vinyl siding is a screened wall cladding system, flashing details should be accomplished in 

the plane of the drainage plane (building paper or house wrap, rigid foam or sheathing), not the cladding. 

Do not caulk siding and do not rely on the "J"-channel as part of the drainage plane. (In other words, 

never consider vinyl siding, aluminum siding, or any siding for that matter, as the weather barrier). 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Stepped Foundation Insulation Detail 

Maintaining thermal barrier continuity in stepped foundations has proven difficult or easy to neglect. 

Figure 2-5 shows how the rigid foam needs to be cut and placed. 

Energy Trusses 

A number of different truss configurations yield greater depth at the heel, but they vary quite a bit in cost. 

The truss shown in Figure 2-5 (sometimes called a “slider” truss) has proven to be among the most costcompetitive. And of course, the pitch of the roof affects just how much insulation you can get at this 

location, regardless of the type of truss. 

Material Compatibility and Substitutions 

Rim Joist Material 

With claddings such as vinyl siding that track the dimensional changes in structural materials to which 

they are attached, a rim joist material such as engineered lumber is recommended because it is more 

dimensionally stable (less shrinkage) than solid sawn material. 

 

Figure 2-5. Stepped foundation detail on the left and trusses on the right 
 

2-14

Rim Joist Blocking 

An alternative to this detail is to spray foam insulation on the rim joist to maintain air barrier continuity at 

this transition. 

Drainage Plane on Rigid Insulation 

An alternative to flashing, shiplapping, or sealing the XPS insulation for continuity of the drainage plane, 

is to apply a housewrap to the outside of the insulation. The housewrap then becomes the continuous 

drainage plane. It is also possible to install the housewrap under the XPS insulation (this is a more 

common commercial wall system approach). 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint 

will result in severely limiting or eliminating any drying potential that the wall assembly has to the 

interior. These interior treatments are not recommended. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, kitchens, are excellent candidates for 

non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 

Cast Concrete Foundation Walls 

If block is used instead of cast concrete for foundation walls, the bond beam becomes essential to 

maintain air barrier continuity at the top of the block wall. 

L-channel Detail on Cladding at Base of Exterior Wall 

Any stop can be used at the bottom, exposed edge of the rigid insulation to prevent insect and rodent 

intrusion, as long as it does not interfere with the foam’s function as the drainage plane. 
 

2-15

Building Profile #6. The Denver 

Foundation: Basement w/sub-crawl Attic: Unconditioned Cladding (1st floor): Brick veneer 

Above Grade Walls: Wood frame Roof: Asphalt shingles Cladding (2nd floor): Wood siding 

Figure 2-6. Cross section of the Denver 
 

2-16

Building Science Details 

Ducts in Conditioned Space 

The Denver (Figure 2-6) is designed to accommodate HVAC equipment and ducts in the basement and 

living space, not in the unconditioned attic. HVAC ducts should not be run in exterior walls. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists, 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draftstopping material (wood blocking) and 

sealant/caulk, or spray foam. Note that neither nor fiberglass (batt or blown) can be used for the air 

barrier. The air barrier detail on second-story band joists is important because it is inaccessible (covered 

by structural/finish floor and ceiling finish) after construction. Note that while fiberglass batts fulfill the 

requirement for protection from ignition in the open band joists, fiberglass batt material by itself cannot 

maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 2-7 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. See also www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Figure 2-7. Creating a continuous air barrier 
 

2-17

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

www.buildingscience.com/resources/walls/insulation_sheathing.pdf. 

In cold climates, the moisture load in the winter months is primarily from the interior, so roof and wall 

assemblies are designed to dry primarily to the exterior. Wintertime condensation control can be 

facilitated by elevating the temperature of the first condensing surface (the outside of the exterior 

sheathing) via the use of insulating sheathing. When XPS (with relatively low permeability) is used, then 

only slow drying is available to the exterior. Accordingly, the majority of drying occurs to the interior 

during the summer months. Therefore, interior vapor barriers should not be installed. Note that there is a 

difference between an interior vapor barrier and an interior vapor retarder. Particular care must be taken 

to prevent the entry of bulk water (i.e., leaks) and control interior relative humidity in the coldest months. 

See Material Compatibility and Substitutions. 

Drainage Plane, Air Barrier, Vapor Control 

On the second story, the drainage plane is the housewrap—it must be weatherlapped at any horizontal 

joints. On the first story, the rigid insulation becomes the drainage plane—all vertical joints must be 

shiplapped, flashed, or sealed; all horizontal joints must be sealed or taped. Note how flashing maintains 

the continuity of the drainage plane at transitions. 

This building profile has a continuous air barrier on both the interior (Airtight Drywall Approach on 

ceiling and walls—see www.buildingscience.com/housesthatwork/airsealing/default.htm) and the exterior 

walls (the housewrap on the second story and sealed rigid insulation on the first story). 

In cold climates, walls are generally designed to dry to the exterior, with the exterior of the wall being 

five times more vapor permeable than the interior, or they are designed with insulating sheathing in order 

to control the temperature of the condensing surfaces. The thickness of the insulating sheathing is 

determined by calculation based on the severity of the climate (see “Insulations, Sheathings and Vapor 

Diffusion Retarders” at www.buildingscience.com/resources). Walls constructed with insulating sheathing 

are designed to dry to the interior during the summer months. Latex paint or some other vapor retarder 

(i.e., the kraft facing on fiberglass batts or CertainTeed’s MemBrainTM Smart Vapor Retarder) acts to 

slow moisture entry in to the framed assembly from the interior during the winter. Ideally, the more vapor 

permeable EPS rigid insulation works well as the thickness of insulation goes beyond 1 in. (see Field 

Experience Notes for more discussion). 

Rough Opening Flashing 

See Figure 2-8 for details on the brick veneer flashing (for drainage plane continuity). For more details, 

see the EEBA Water Management Guide at www.eeba.org/bookstore. 

Advanced Framing 

On the first story, structural sheathing is replaced with cross bracing or some alternative for shear 

resistance in the wall assembly. Thermal performance and reduced drywall cracking are additional 

benefits of a comprehensive approach. See 

www.buildingscience.com/housesthatwork/advancedframing/default.htm for details. 
 

2-18

Figure 2-8. Brick veneer flashing 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). In 

this profile, only garage walls would be affected. 

Soil Gas Ventilation 

Soil gas ventilation is accomplished by the continuous exhaust ventilation system in the structural subcrawlspace. Radon, soil moisture, and any volatilized organic substances that may be in the soil from 

previous land use (such as agriculture) are all handled with this exhaust system. The continuous 

polyethylene sheeting should still be installed on the floor of the sub-crawl to reduce the soil gas load that 

the continuous exhaust ventilation system handles. Alternatively, a passive system exiting through the 

roof can be used. 

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate where the average monthly 

temperature for the coldest month of the year goes below 45°F. The heat loss through the basement walls 

is significant enough to warrant 1-1/2 to 2 in. of rigid insulation. Note that the insulation must either 

comply with local codes for protection against ignition or be covered with material such as gypsum 

wallboard. 

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity 

is often the condition that requires higher ventilation rates. They can also depressurize the house causing 

loss of conditioned air. Generally, the area of the gable and soffit vents combined with the leakage of the 

attic ceiling is such that the fan pulls air not just from the exterior vent, but also from the conditioned 

space below. 
 

2-19

Climate-Specific Details 

Below-Grade Insulation 

Ground temperatures make foundation wall and slab insulation an important part of the thermal barrier. 

Above-Grade Insulation 

Homes in this climate benefit from exterior insulation that warms whatever structural material is to its 

interior, protecting it from the moisture degradation that can occur as the result of condensation. 

Ice Dam Protection 

The combination of sufficient roof pitch, adequate insulation just above the exterior wall, and air sealing 

at the wall-roof assemblies transition is essential to prevent ice dams. But ice dams can occur even in 

properly detailed roof assemblies from differential solar snow melt. A water protection membrane at the 

eave is recommended on all roof assemblies in this climate. 

Mechanical Systems 

Heating and Cooling. A sealed combustion hot air furnace and SEER 12 air conditioning unit is 

recommended. A single central return requires transfer grilles to provide return path and avoid 

pressurizing bedrooms (Figure 2-9). 

Figure 2-9. Return grilles 
 

2-20

Ventilation. For homes with central forced air distribution system, we recommend an intermittent 

central-fan-integrated supply, designed to provide the ASHRAE 62.2P recommended rate, with fan 

cycling control set to operate the central air handler 20 minutes every hour to provide ventilation air 

distribution and whole-house averaging of air quality and comfort conditions ($125 to $150). Outside air 

fraction should be designed to keep mixed air temperature at the furnace heat exchanger above 50°F, 

usually not more than a 10%. Include a normally closed motorized damper in the outside air duct (+$50 to 

$60) (Figure 2-10). 

 

Basement Configuration 

Figure 2-10. Recommended ventilation system 
 

2-21

For homes without central forced air distribution system. Continuous multi-point exhaust, designed 

to provide the ASHRAE 62.2P recommended flow rate, pulling from each bedroom (unless the bedroom 

has a bathroom, in which case it will pull from the bathroom), and pulling from at least one location in the 

principal living area. Any combustion appliances must be power-direct vented sealed combustion. 

Water heater. Any type of gas water heater (in terms of venting) is adequate if the water heater is 

located in the garage. If the water heater is located inside conditioned space, then it must be a gas power 

vented or power-direct vented unit, or an electric water heater. 

Structural Sub-crawlspace 

This detail is actually soil- rather than climate-specific. For areas with expansive soils, the simplest 

solution is to build post-tensioned slab-on-grade foundations that “float” over and in expansive soils. If 

homes must have basements, the structural sub-crawlspace resists the lateral forces of expanding soils, 

while deep piles carry the house structural load to bear on deep stable material. This sub-structural 

crawlspace must have a continuous vapor barrier ground cover and must be vented to prevent moisture 

problems. A continuous 50 to 100 cfm exhaust fan accomplishes this ventilation without any significant 

or real effect on the pressure balance within the basement, the rest of the home, or with any combustion 

sources that may be in the home (50 cfm for homes 2,000 ft2

 or less, and 100 cfm for homes more than 

2,000 ft2

). 

Insect Management 

In cold climates, insect pressure (termites and carpenter ants) is less pronounced than in warmer climates, 

but important nonetheless. A three-pronged approach deals with the three things insects need—cover, 

moisture, and food (wood or paper): 

Reduced cover: Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the foundation. 

Control moisture: Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment: Use an environmentally appropriate building materials treatment (such as BoraCare®) for insect-prone, near-grade wood materials. 

Inter-relationship of first three points: Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with others. For example, if for some reason chemical treatment of 

soil or building materials is not an option, then complete rigor in moisture control and ground cover is 

required. 

Field Experience Notes 

Selection of Rigid Insulation 

Most builders select rigid insulation based on costs and handling properties. Although the vapor 

permeability of both EPS and rigid fiberglass insulation can make them particularly well suited to cold 

climate envelope assemblies, their lack of availability and user-friendliness generally make XPS 

insulation the builder choice. For these reasons, we recommend 1-in. or thicker XPS in most wall 

assemblies. But remember, the type of sheathing to use is always a question that should be asked in the 

context of the given cladding and the level of control that can be expected over interior relative humidity 

via mechanical ventilation. See “Insulations, Sheathings, and Vapor Diffusion Retarders” for more 

information (www.buildingscience.com/resources). 
 

2-22

Joint Treatment in Rigid Insulation 

Shiplapped rigid foam insulation has proven to be available in only very limited areas. Mastic works as a 

water sealant but its long-term performance is not known (although it appears promising). The flexible 

flashing with polyethylene film is straightforward and creates a natural weatherlap and therefore is the 

preferred approach. 

Reservoir Claddings 

Solar-driven moisture can be a significant problem with cladding such as wood clapboards and brick if 

wind, rain, and sun work together to saturate the siding and then drive this moisture into the wall 

assembly. The primary defense against this is the continuous back-venting of the air space interior to the 

cladding. The low permeability of the material just to the interior of the air space is a secondary defense. 

A 3/8-in. space works well for the wood clapboard (large enough for free flow of water and air and not 

large enough to create problems at windows, doors, or cornerboards). For more information on this topic, 

see www.buildingscience.com/resources/walls/solar_driven_moisture_brick.htm. A 1-in. air space and 

open head joints (top and bottom of wall) are required for the brick veneer. Harking back to "old-timer" 

practices—one could place a thin sand layer at the bottom of the 1-in. air space (to act as a bond break for 

mortar droppings) and leave bricks out intermittently in the first course. After the veneer is completed, the 

sand and mortar droppings can be easily removed and the missing bottom course brick mortared in. 

Brick Ties 

The two-piece adjustable ties are strongly recommended, given the 1-in. air space and foam insulation. 

See the Masonry Institute Technical Notes at www.brickinfo.org/pdfs/44b.pdf. 

Brick Shelf in Foundation Wall 

The brick veneer "seat" is readily accomplished by securing dimensional lumber of the desired size to the 

inside top edge of the concrete form. 

Perimeter Drainage in Expansive Soils 

The plastic trough in which the perforated drain pipe is placed in this assembly prevents water collected 

in the pipe from passing into the soil around the foundation pilings. This is an important foundation detail 

in expansive soils. 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Stepped Foundation Insulation Detail 

Maintaining thermal barrier continuity in stepped foundations has proven difficult, or easy, to neglect. 

Figure 2-11 shows how the rigid foam needs to be cut and placed. 

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 2-11 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss. 

 
 

2-23

Material Compatibility and Substitutions 

Exterior Sheathing 

On the second story of this building, cavity-warming rigid insulation (usually strongly recommended for 

cold climates) is lacking. It is, therefore, doubly important that the exterior elements of this wall be vapor 

permeable or vapor semi-permeable. A material such as fiberglass-faced gypsum board (DensGlass 

Gold®, for example) is more permeable than plywood, which is more permeable than OSB (oriented 

strand board), although all are acceptable. A material such as a faced high-density paperboard (Energy 

Brace® or Thermo-ply®, for example) is vapor impermeable and is not recommended in this climate. See 

Table 1: Building Materials Property Table for more information. 

Rim Joist Blocking 

An alternative to this detail is to spray foam insulation on the rim joist to maintain air barrier continuity at 

this transition. 

Drainage Plane on Rigid Insulation 

An alternative to flashing, shiplapping, or sealing the XPS insulation for continuity of the drainage plane 

is to apply a housewrap to the outside of the insulation. The housewrap then becomes the continuous 

drainage plane. It is also possible to install the housewrap under the XPS insulation (this is a more 

common commercial wall system approach). 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint 

will result in severely limiting or eliminating any drying potential that the wall assembly has to the 

interior. These interior treatments are not recommended. 

Figure 2-11. Trusses and stepped foundations 
 

2-24

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Floor System Between Basement and Sub-Crawl 

We selected the cast concrete system as the most robust and moisture resistant of the options—wood, 

steel, and concrete. 

Gypsum Wallboard 

Areas of potentially high moisture (such as bathrooms, basements, and kitchens) are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 
 

2-25

Building Profile #7. The Minneapolis 

Foundation: Slab-on-grade Attic: Vented cathedral ceiling Cladding: Stucco 

Above Grade Walls: Wood frame Roof: Asphalt shingles 

Figure 2-12. Cross section of the Minneapolis
 

2-26

Building Science Details 

Cathedralized Roof 

This roof assembly has continuous back-venting from eave to ridge of the structural roof deck, providing 

higher drying potential of the assembly to the exterior. This, in combination with the low vapor 

permeability of the rigid insulation on the interior of the assembly that keeps interior moisture out of the 

roof assembly, makes for a robust, cold-climate, cathedralized system. 

Ducts in Conditioned Space 

This building profile accommodates HVAC equipment and ducts in the living space. HVAC ducts should 

not be run in exterior walls or in the slab where an increased potential for condensation exists. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists, 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draftstopping material (wood blocking) and 

sealant/caulk, or spray foam. Note that neither nor fiberglass (batt or blown) can be used for the air 

barrier. The air barrier detail on second-story band joists is important because it is inaccessible (covered 

by structural/finish floor and ceiling finish) after construction. Note that while fiberglass batts fulfill the 

requirement for protection from ignition in the open band joists, fiberglass batt material by itself cannot 

maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 2-13 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space (see also www.buildingscience.com/housesthatwork/airsealing/default.htm). 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

Figure 2-13. Creating a continuous air barrier 
 

2-27

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls/insulation_sheathings.pdf). 

In cold climates, the moisture load in the winter months is primarily from the interior, so roof and wall 

assemblies are generally designed to dry primarily to the exterior. Wintertime condensation control can be 

facilitated by elevating the temperature of the first condensing surface (the outside of the exterior 

sheathing) via the use of insulating sheathing. When XPS (with relatively low permeability) is used, then 

only slow drying is available to the exterior. Accordingly, the majority of drying occurs to the interior 

during the summer months. Therefore, interior vapor barriers should not be installed. Note that there is a 

difference between an interior vapor barrier and an interior vapor retarder. Particular care must be taken 

to prevent the entry of bulk water (i.e., leaks) and to control interior relative humidity in the coldest 

months (see Material Compatibility and Substitutions). 

Drainage Plane, Air Barrier, Vapor Control 

The drainage plane on this stucco-clad wall assembly is the building paper (in this case, StuccoWrap®). 

This building profile has a continuous air barrier on both the interior (Airtight Drywall Approach on 

ceiling and walls―see www.buildingscience.com/housesthatwork/airsealing/default.htm) and the exterior 

walls (sealed rigid insulation). Note that framing of the second story knee wall after the rigid insulation is 

installed makes for a continuous air barrier at the roof line. 

In cold climates, walls are generally designed to dry to the exterior, with the exterior of the wall being 

five times more vapor permeable than the interior, or they are designed with insulating sheathing in order 

to control the temperature of the condensing surfaces. The thickness of the insulating sheathing is 

determined by calculation based on the severity of the climate (see “Insulations, Sheathings and Vapor 

Diffusion Retarders” at www.buildingscience.com/resources). Walls constructed with insulating sheathing 

are designed to dry to the interior during the summer months. Latex paint or some other vapor retarder 

(i.e., the kraft facing on fiberglass batts or CertainTeed’s MemBrainTM Smart Vapor Retarder) acts to 

slow moisture entry in to the framed assembly from the interior during the winter. Ideally, the more vapor 

permeable EPS rigid insulation works well as the thickness of insulation goes beyond 1 in. (see Field 

Experience Notes for more discussion). 

Rough Opening Flashing 

Because the drainage plane is the StuccoWrap, flashing details must occur at this point in the wall 

assembly. See the EEBA Water Management Guide at www.eeba.org/bookstore for flashing details. 

Advanced Framing 

Although roof trusses that accommodate second floor half-stories are available, solid sawn framing may 

be more practical and cost-effective and must be used with the thermal barrier details shown in this 

assembly. The 24-in., on-center spacing, single-top plate, and in-line framing are strongly recommended 

in this climate because of the clear benefits in terms of thermal performance and reduced drywall 

cracking. See www.buildingscience.com/housesthatwork/advancedframing/default.htm for details. 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 
 

2-28

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult, if not impossible, to assess before 

completion of the structure—resultant confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate where the average monthly 

temperature for the coldest month of the year goes below 45°F. The heat loss through the basement walls 

is significant enough to warrant 1-1/2 to 2 in. of rigid insulation. Note that the insulation must either 

comply with local codes for protection against ignition or be covered with material such as gypsum 

wallboard. 

Climate-Specific Details 

Below-Grade Insulation 

The combination of stem wall and slab insulation is an important element in reducing heat loss and 

preventing condensation. Note the thermal break provided by the rigid insulation separating the slab from 

the concrete stem wall. 

Above-Grade Insulation 

Homes in this climate benefit from exterior insulation that warms whatever structural material is to its 

interior, protecting it from the moisture degradation that can occur as the result of condensation. 

Ice Dam Protection 

The combination of sufficient roof pitch, adequate insulation just above the exterior wall, and air sealing 

at the wall-roof assemblies transition is essential to prevent ice dams. But ice dams can occur even in 

properly detailed roof assemblies from differential solar snow melt. A water protection membrane at the 

eave is recommended on all roof assemblies in this climate. 

Stucco Cladding 

This polymer-modified stucco wall assembly is water-managed as a drain-screen system. For more 

information on water management strategies for different building assemblies in different climates and 

levels of precipitation, see the appropriate EEBA Builder’s Guide (www.eeba.org/bookstore). 

HVAC Configuration 

For homes with central forced air distribution system, an intermittent central-fan-integrated supply 

ventilation system is recommended. The system should be designed to provide the ASHRAE 62.2P 

recommended flow rate, with fan cycling control set to operate the central air handler 20 minutes every 

hour to provide distribution of ventilation air and whole-house averaging of air quality and comfort 

conditions ($125 to $150). The outside air fraction should be designed to keep mixed air temperature at 

the furnace heat exchanger above 50°F, usually not more than 10%. Include a normally closed motorized 

damper in the outside air duct (+$50 to $60) (Figure 2-14). 

For homes without a central forced-air distribution system, we recommend a continuous multi-point 

exhaust, designed to provide the ASHRAE 62.2P recommended flow rate. This would pull from each 

bedroom (unless the bedroom has a bathroom, in which case it will pull from the bathroom ) and from at 

least one location in the principal living area. Any combustion appliances must be power-direct vented 

sealed combustion. 
 

2-29

Figure 2-14. HVAC configuration 

Insect Management 

In cold climates, insect pressure (termites and carpenter ants) is less pronounced than in warmer climates, 

but is important nonetheless. A three-pronged approach deals with the three things insects need—cover, 

moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the foundation. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate building materials treatment (such as BoraCare®) for insect-prone, near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with others. For example, if for some reason, chemical treatment of 

soil or building materials is not an option, then complete rigor in moisture control and ground cover is 

required. 

Field Experience Notes 

Selection of Rigid Insulation 

Most builders select rigid insulation based on costs and handling properties. Although the vapor 

permeability of both EPS and rigid fiberglass insulation can make them particularly well suited to cold 

climate envelope assemblies, their lack of both availability and user-friendliness generally make XPS 
 

2-30

insulation the builder choice. For these reasons, we recommend 1-in. or thicker XPS in most wall 

assemblies. But remember, the type of sheathing to use is always a question that should be asked in the 

context of the following: 

• The given cladding; and 

• The level of control that can be expected over interior relative humidity via mechanical 

ventilation. (See “Insulations, Sheathings, and Vapor Diffusion Retarders” for more information 

www.buildingscience.com/resources). 

Joint Treatment in Rigid Insulation 

Shiplapped rigid foam insulation has proven to be available in only very limited areas. Mastic works as a 

water sealant but its long-term performance is not known (although it appears promising). The flexible 

flashing with polyethylene film is straightforward and creates a natural weatherlap and, therefore, is the 

preferred approach. 

Stucco Flashing Detail 

Where a roof intersects an exterior wall (for example, on a garage attached to a gable end), the flashing 

detail for the stucco should look like Figure 2-15 and employ a kick-out flashing. 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/1619_Yost&Edminster_for_au.pdf.

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 2-16 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss.
 

2-31

Figure 2-16. A “slider” truss 

Figure 2-15. Stucco flashing 
 

2-32

Material Compatibility and Substitutions 

Slab Foundation 

A monolithic slab with rigid insulation extending out below grade horizontally (shallow frost-protected 

foundation) can be used in this climate for slab-on-grade foundations. For more details, see Figure 2-17 

and the American Society of Civil Engineers standard, "Design and Construction of Frost-Protected 

Shallow Foundations” (www.pubs.asce.org/BOOKdisplay.cgi?9991154). 

Flooring 

Many finished flooring materials—either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example)—should only be installed over a slab with a low 

w/c ratio (≈ 0.45 or less) or a slab allowed to dry (<0.3 grams/24hrs/ft2

) before installation of flooring. In 

general, sheet vinyl flooring should be avoided. 

Figure 2-17. Slab foundation details 
 

2-33

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint 

will result in severely limiting or eliminating any drying potential that the wall assembly has to the 

interior. These interior treatments should be avoided. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Stucco 

Given the annual rainfall for the Minneapolis region, traditional stucco should not be substituted for 

polymer-modified stucco. A material such as DensGlass Gold® can be used as sheathing and function as 

the drainage plane with mastic used to seal all joints. 

Slab Insulation 

A polyethylene vapor barrier is not necessary with this design because of the moisture control properties 

of the rigid insulation. If a polyethylene vapor barrier is installed with the rigid insulation, it must be 

installed on top of the rigid insulation in direct contact with the concrete. A sand layer should not be 

placed between the polyethylene or rigid insulation and the concrete slab. The polyethylene should never 

be installed under the rigid insulation. See also “Why Sand Layers Should Not Be Placed Under Slabs” at 

www.buildingscience.com/resources/foundations/sand_layers_under_slab.htm.

Gypsum Wallboard 

Areas of potentially high moisture (such as bathrooms, basements, and kitchens) are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 
 

3-1

III. Houses That Work for Mixed-Humid Climates 

Introduction 

For the purpose of defining best practices in this report, a mixed-humid climate is considered a region that 

receives more than 20 in. of annual precipitation, has approximately 4,500 heating degree days or fewer, 

and where the monthly average outdoor temperature drops below 45°F during the winter months. This 

winter temperature limit establishes a “southern” boundary for this climate region and provides the 

rationale for differentiating regions where unvented roofs can be constructed without controlling the 

temperature of the roof deck, using insulation to address wintertime condensation. 

This is a particularly challenging climate—we have significant heating, significant cooling, high moisture 

levels most of the year, and many areas of moderate to high rainfall. Controlling the infiltration of 

moisture-laden air into the building envelope and keeping moisture away from cold surfaces are major 

goals of design and construction. Ideally, wall and roof assemblies are designed to promote drying to both 

the interior and exterior in this climate. 

For the Mixed-Humid climate we have chosen three Building Profiles that we think best represent the 

climate and regional building practices: 

• The “Charlotte” —two-story, stick-framed, conditioned crawlspace, first floor brick veneer, 

second-floor wood lap siding, vented attic, asphalt shingle roof (Figure 3-1) 

• The “Atlanta” —two-story, stick-framed, slab-on-grade, both stories vinyl sided, vented attic, 

asphalt-shingle roof (Figure 3-7) 

• The “Louisville” —one-story, stick-framed, full basement, vinyl siding, cathedral ceiling (no 

attic), asphalt-shingle roof (Figure 3-14). 

A substantial amount of repetition is present in these Building Profiles, but is necessary in order to 

provide comprehensive, stand-alone, examples of performance packages that achieve 40% energy savings 

while maintaining or improving quality and durability. 

For information about a production builder in a Mixed-Humid climate see 

www.buildingscience.com/buildingamerica/casestudies/default.htm. This case study explores the builder's 

experience with the Building America program and discusses the reasons for the specific design and 

construction details that are used at Health-E Community Enterprises. To see detailed drawings on 

Advanced Framing and Air Sealing Techniques go to 

www.buildingscience.com/housesthatwork/advancedframing/default.htm. Additional information on 

construction methods and alternative designs is included in the EEBA Builder's Guide for Mixed-Humid 

Climates (www.eeba.org/bookstore). 
 

3-2

Building America Best Practices for Mixed-Humid Climates 

High-performance Building America homes in mixed-humid climates are faced with a significant heating 

season (typically up to 4,500 heating degree days and monthly average outdoor temperatures dropping 

below 45oF during winter months), as well as a cooling season with significant latent load. Reducing solar 

gain, using energy conserving appliances and compact fluorescent lighting reduces the sensible load. This 

affects the ability of the air conditioner to remove moisture or dehumidify the air because the latent load 

is a larger fraction of total cooling load. Therefore, correct sizing of air conditioning systems is especially 

important in the control of interior humidity in mixed-humid climates. Oversizing air conditioning 

systems in this climate typically leads to moisture problems. 

The following Best Practices are based on our Building America Performance Targets 

(www.buildingscience.com/buildingamerica/targets.htm) and are reflected in the three Mixed-Humid 

Building Profiles, the “Charlotte,” the “Atlanta,” and the “Louisville.” All climate-specific Best Practices 

are identified with a bolded and bracketed [HH]. 

Process: Building Design, Systems Engineering, and Commissioning 

Design for Energy Performance 

Energy performance for space conditioning and hot water is 40% better than the 1995 Model Energy 

Code base case house (i.e., equal to 10% better than ENERGY STAR® performance requirements). 

Systems Engineering 

Design structure using advanced framing methods (see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm or 

www.buildingscience.com/resources/presentations/advanced_framing.pdf). 

Design structure to accommodate the most efficient duct distribution system that places all ducts and air 

handling equipment within conditioned space (see 

www.buildingscience.com/resources/misc/wood_efficiency.pdf; specifically Figure 3 and page 5). 

Design and detail structure for durability, in terms of wall and roof assembly drying potential, continuous 

drainage plane, and continuous thermal barrier that clearly defines the conditioned space (see Building 

Profiles). [MH] 

Commissioning: Performance Testing 

Air leakage (determined by blower door depressurization testing) should be less than 2.5 in.2/100 ft2

surface area leakage ratio (CGSB, calculated at a 10-Pa pressure differential); or 1.25 in.2

/100 ft2 leakage 

ratio (ASTM, calculated at a 4-Pa pressure differential); or 0.25 cfm/ft2

 of building envelope surface area 

at a 50-Pa air pressure differential. If the house is divided into multiple conditioned zones, such as a 

conditioned attic or conditioned crawl space, the blower door requirement must be met with the access to 

the space open, connecting the zones. 

Ductwork leakage to the exterior for ducts distributing conditioned air should be limited to 5% of the total 

air-handling system rated air flow at high speed (nominal 400 cfm per ton) determined by pressurization 

testing at 25 Pa. Two acceptable compliance mechanisms are (1) test duct leakage to outside at finish 

stage or (2) test total duct leakage at duct rough-in stage. 

Forced air systems that distribute air for heating and cooling should be designed to supply airflow to all 

conditioned spaces and zones (bedrooms, hallways, basements) as well as to provide a return path from 

all conditioned spaces or zones. Interzonal air pressure differences, when doors are closed, should be 
 

3-3

limited to 3 Pa. This is typically achieved by installing properly sized transfer grilles or jump ducts (see 

www.buildingscience.com/resources/mechanical/transfer_grille_detail.pdf and 

www.buildingscience.com/resources/mechanical/transfer_grille_sizing_charts.pdf). 

Mechanical ventilation system airflow should be tested during commissioning of the building. 

Testing of the house should be completed as part of the commissioning process. The SNAPSHOT form 

is available for download as a convenient way to record the testing information (see 

www.buildingscience.com/buildingamerica/snapshot_form.pdf). Instructions for completing the form are 

also available (see www.buildingscience.com/buildingamerica/snapshot_instructions.pdf). Unique or 

custom house plans should each be tested. In a production setting, each model type (i.e., floor plan) 

should be tested until two consecutive houses of this model type meet testing requirements. At that point, 

testing on the same model type can be reduced to a sampling rate of one in seven (i.e., one test, with six 

"referenced" houses). Small additions to a floor plan (e.g., bay window, conversion of den to bedroom) 

should be considered the same model type; major changes (e.g., bonus room over the garage, conversion 

of garage into a hobby room, etc.) should be considered a separate model type. 

Site: Drainage, Pest Control, and Landscaping 

Drainage 

Grading and landscaping shall be planned for movement of building run-off away from the home and its 

foundation, with roof drainage directed at least 3 ft beyond the building, and a surface grade of at least 

5% maintained for at least 10 ft around and away from the entire structure. 

Pest Control 

Based on local code and Termite Infestation Probability (TIP) maps, use environmentally appropriate 

termite treatments, bait systems, and treated building materials that are near or have ground contact (see 

www.uky.edu/Agriculture/Entomology/entfacts/) [MH] 

Landscaping 

Plantings should be held back as much as 3 ft and no less than 18 in. from the finished structure, with any 

supporting irrigation directed away from the finished structure. Decorative ground cover—mulch or pea 

stone, for example—should be thinned to no more than 2 in. for the first 18 in. from the finished structure 

(see Building Profiles). [MH] 

Foundation: Moisture Control and Energy Performance 

Moisture Control 

The building foundation shall be designed and constructed to prevent the entry of moisture and other soil 

gases (see Building Profiles). [MH] 

Slabs require a 6-mil polyethylene vapor barrier directly beneath the concrete or an equivalent approach 

(such as rigid insulation) that accomplishes vapor control for the slab. The vapor retarder must 

continuously wrap the slab as well as the grade beam. 

Sub-slab drainage shall consist of a granular capillary break directly beneath the slab vapor retarder. 

Use radon resistant construction practices as described on the EPA radon control web site 

(www.epa.gov/iaq/radon/construc.html). 
 

3-4

Energy Performance 

Slabs in this climate shall be insulated at the perimeter (energy modeling reveals significant heat loss at 

this portion of the building envelope during the heating season). Consider the use of borate-treated rigid 

insulation on the slab perimeter (see Building Profiles and photo detail at 

www.buildingscience.com/buildingamerica/casestudies/fairburn.htm). [MH] 

Envelope: Moisture Control and Energy Performance 

Moisture Control 

Water management. Roof and wall assemblies must contain elements that provide drainage in a 

continuous manner over the entire surface area of the building enclosure, including lapped flashing 

systems at all penetrations. See the Building Profiles and the EEBA Water Management Guide for 

specific details for various wall assemblies. [MH]

Vapor management. Roof and wall assemblies must contain elements that, individually and in 

combination, permit drying of interstitial spaces. See the Building Profiles. [MH]

Energy Performance 

Air leakage. The exterior air flow retarder (foam sheathing) or interior air flow retarder (gypsum board) 

is sealed to the slab and frame walls (Airtight Drywall Approach [ADA]). For details of the ADA for 

interior air flow retarders, see www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Windows. We recommend one of two approaches: 

• U-factor 0.35 or lower and SHGC (solar heat gain coefficient) 0.35 or less, regardless of climate 

• Climate or orientation-specific glazing properties if the builder can employ passive solar orientation 

and design concepts, and occupants can be expected to operate window shading in concert with 

time of day and weather conditions. [MH]

Mechanicals / Electrical / Plumbing 

Systems Engineering 

HVAC system design, both equipment and duct, should be done as an integral part of the architectural 

design process. HVAC system sizing should follow ACCA Manual J and duct sizing should follow 

Manual D (see www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf).

Mechanical ventilation should be an integral part of the HVAC system design (see the Building Profiles 

and www.buildingscience.com/resources/mechanical/advanced_space_conditioning.pdf). [MH] 

Energy Performance 

Air conditioner or heat pump shall be installed according to best practices (see 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf).

Major appliances should meet high-energy efficiency standards using current appliance ratings. Only 

those appliances in the top one-third of the DOE Energy Guide rating scale should be selected. (For 

details, see www.eren.doe.gov/consumerinfo/energy_savers/appliances.html.)
 

3-5

Occupant Health and Safety 

Base rate ventilation. The mechanical ventilation is controlled per ASHRAE Standard 62.2. 

Spot ventilation. Intermittent spot ventilation of 100 cfm should be provided for each kitchen; all kitchen 

range hoods must be vented to the outside (no recirculating hoods). Intermittent spot ventilation of 50 

cfm, or continuous ventilation of 20 cfm when the building is occupied should be provided for each 

washroom/bathroom.

All combustion appliances in the conditioned space must be sealed combustion or power vented. 

Specifically, any furnace inside conditioned space should be a sealed-combustion 90%+ unit. Any water 

heater inside conditioned space should be power vented or power-direct vented. Designs that incorporate 

passive combustion air supply openings or outdoor supply air ducts not directly connected to the 

appliance should be avoided.

Provide filtration systems for forced air systems that provide a minimum atmospheric dust spot efficiency 

of 30% or MERV of 6 or higher.

Indoor humidity should be maintained in the range of 25 to 60% by controlled mechanical ventilation, 

mechanical cooling, or dehumidification (see 

www.buildingscience.com/resources/moisture/relative_humidity_0402.pdf).

Carbon monoxide detectors (hard-wired units) shall be installed (at one per every approximate 1000 ft2

) 

in any house containing combustion appliances and/or an attached garage.

Information relating to the safe, healthy, comfortable operation and maintenance of the building and 

systems that provide control over space conditioning, hot water or lighting energy use shall be provided to 

occupants.

Envelope/Mechanicals Management 

Plumbing. No plumbing in exterior walls. Air seal around plumbing penetrations in the pressure 

boundary (air barrier), such as rim (band) joist or ceiling. 

Electrical. Seal around wires penetrating the air barrier or pressure boundary. 
 

3-6

Building Profile #8. The Charlotte 

Foundation: Conditioned crawl space Attic: Unconditioned Cladding (1st): Brick veneer 

Above Grade Walls: Wood frame Roof: Asphalt shingles Cladding (2nd): Wood siding 

Figure 3-1. Cross section of the Charlotte 
 

3-7

Building Science Details 

Ducts in Conditioned Space 

This building profile (Figure 3-1) is designed to accommodate HVAC equipment and ducts in either the 

living space or in the conditioned crawlspace. HVAC ducts should not be run in exterior walls. 

Conditioned Crawlspace 

Conditioning of the crawlspace means that this space must be constructed much like a living space—it 

must be supplied by the HVAC system and have a transfer grille to the living space to return air back to 

the HVAC system. The supply air should be directed horizontally across the crawlspace with good 

enough “throw” to provide some mixing, not directed down at the floor. Sizing of the supply air should be 

about 5% of the conditioned crawlspace floor area (For example: 0.05 cfm/ft2

*1600 ft2 = 80 cfm for a 

1,600 ft2

 conditioned crawlspace). A single 6-in. diameter supply duct typically suffices. Transfer air 

should go back to the central area of the living space above the crawlspace. Two grilles (10 in. by 4 in.) 

on opposite sides of the crawlspace are usually sufficient. The transfer area should be calculated in the 

same manner as for closed bedrooms connecting to hallways, using the 3-Pa pressure difference limit. 

Some form of mechanical moisture control for the crawlspace is necessary. We recommend one of the 

following approaches: 

1. A controlled ventilation strategy using the intermittent central fan-integrated supply—it provides 

both mixing and moisture removal for the crawlspace as well as the house. 

2. A stand-alone dehumidifier installed in the crawlspace. 

3. A continuously operating crawlspace exhaust fan with make-up air extracted from the house. 

In the Charlotte, the rigid insulation is applied to the interior face of the exterior foundation walls. 

Moisture control is important to proper performance, in particular the vapor barrier ground cover on the 

floor of the crawlspace. The vapor barrier must be continuous and sealed to the perimeter wall and any 

supporting piers. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draft-stopping material (wood blocking) and 

sealant/caulk, or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the 

air barrier. The air barrier detail on second-story band joists is important because it is inaccessible 

(covered by structural/finish floor and ceiling finish) after construction. The air barrier/thermal barrier 

detail is important on ground floor band joists because of the thermal bridge that can occur at the top of 

basement and crawlspace foundation walls (as the result of the air barrier and thermal barrier moving 

from the outside to the inside of the building envelope and termite inspection zones located at the top of 

basement and crawlspace foundation walls). Note that while fiberglass batts fulfill the requirement for 

protection from ignition in the open band joists, fiberglass batt material by itself cannot maintain the air 

barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 3-1 for details in terms of using 
 

3-8

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. For more details see Figure 3-2 and 

www.buildingscience.com/housesthatwork/airsealing/default.htm ). 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls/insulation_sheatings.pdf). 

In Mixed-Humid climates, roof and wall assemblies are best designed to dry to both the exterior and 

interior. This is not always possible when rigid exterior insulating sheathings are used because of their 

low vapor permeability. With insulating sheathings only inward drying is possible. Accordingly, the 

majority of drying occurs to the interior during the summer months. Therefore, interior vapor barriers 

should not be installed. Note that there is a difference between an interior vapor barrier and an interior 

vapor retarder. Particular care must be taken to prevent the entry of bulk water (i.e., leaks) and to control 

interior relative humidity in the coldest months. See Material Compatibility and Substitutions. The 

moisture potential represented by the reservoir wall claddings is controlled by a fully vented air space. 

The conditioned crawlspace will dry primarily to the exterior, given the vapor permeability of the 

concrete block and brick veneer. 

Figure 3-2. Air sealing 
 

3-9

Drainage Plane, Air Barrier, Vapor Control 

The drainage plane runs along the exterior surface of the foam sheathing. All vertical joints must be 

shiplapped, flashed, or sealed; all horizontal joints must be sealed or taped. 

This building profile has a continuous air barrier on the interior (Airtight Drywall Approach on ceiling 

and walls, see www.buildingscience.com/housesthatwork/airsealing/ default.htm) and on the exterior 

walls (the sealed rigid insulation). 

In Mixed climates, wall and roof assemblies can be designed to dry primarily to the exterior (during the 

heating season), to the interior (during the cooling season), or in both directions. This last approach, the 

bi-directional drying potential, is generally preferred. For more detailed discussion of the three 

approaches, see the discussion of wall and roof design in the EEBA Builder’s Guides

(www.eeba.org/bookstore). Because the permeability of the latex-painted gypsum board is greater than 

that of the XPS rigid insulation, the wall assembly for the “Charlotte” will dry primarily to the interior. 

Rough Opening Flashing 

Flashing must be installed at the plane of the XPS rigid insulation for drainage plane continuity. See 

Figure 3-3 and the EEBA Water Management Guide for sequential flashing details 

(www.eeba.org/bookstore). 

Advanced Framing 

Cross bracing (or other alternative for shear resistance) replaces structural sheathing in this wall 

assembly. Thermal performance and reduced drywall cracking are additional benefits of a comprehensive 

approach to advanced framing (see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm for details). 

Soil Gas Ventilation 

The sub-crawl ground cover to roof vent system handles conditions that are difficult if not impossible to 

assess before completion of the structure—resultant confined concentrations of air-borne radon, soil 

treatments (termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced 

against the cost of the “pound” of cure. 

Figure 3-3. Rough opening flashing 
 

3-10

Sub-crawl Ground Cover Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and an air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 

practical. 

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate where the average monthly 

temperature for the coldest month of the year goes below 45°F. The rule of thumb that BSC uses is 1/4-

in.of rigid insulation per 1,000 heating degree days (HDD). One inch of rigid insulation generally works 

well for this climate. The heat loss through the crawlspace walls is significant enough to warrant 

insulation. Note that the insulation must comply with local codes for protection against ignition. 

Crawlspace Access 

The preferred location for crawlspace access is through the subfloor; any access through the perimeter 

wall must be air sealed and insulated. 

Climate-Specific Details 

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity 

is often the condition that requires higher ventilation rates. They can also depressurize the house causing 

loss of conditioned air. Generally, the area of the gable and soffit vents, combined with the leakage of the 

attic ceiling, is such that the fan pulls air not just from the exterior vent but also from the conditioned 

space below. 

Mechanical systems 

Heating and Cooling. We recommend a sealed combustion 90+ condensing gas furnace or an air-source 

heat pump, ENERGY STAR®-rated or better (HSPF ≥ 8.0, [Heating Seasonal Performance Factor] see 

www.energystar.gov/index.cfm?c=airsrc_heat.pr_as_heat_pumps, follow appropriate sizing procedures). 

For more detailed information, see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

Transfer Grilles. The single central return requires transfer grilles to provide an adequate return air path 

and avoid pressurizing bedrooms, as shown in Figure 3-4. 
 

3-11

Figure 3-4. Transfer grille and jump duct approaches 

Mechanical Ventilation. We recommend an intermittent central-fan-integrated supply, designed to provide 

the ASHRAE 62.2 recommended flow rate, with the fan-cycling control set to operate the central air 

handler 20 minutes every hour to provide ventilation air distribution and whole-house averaging of air 

quality and comfort conditions ($125 to $150). Include a normally closed motorized damper in the 

outside air duct with the AirCyclerTM FRV control (+$50 to $60) (Figure 3-5). 
 

3-12

 

Figure 3-5. Mechanical system and ventilation in conditioned crawlspace

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the foundation. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 
 

3-13

Field Experience Notes 

Termite Control 

Local codes and interpretations by building inspectors can make details involving rigid insulation 

difficult. We have found that the top-of-foundation wall inspection zone shown in this Building Profile 

meets with building official acceptance and results in a limited break in the thermal barrier. 

Air Sealing 

Most codes can be interpreted to require only protection of foam from “ignition” in crawlspaces (“where 

entry is made only for service of utilities ”). The same applies to foam at the rim joist (this is an 

interstitial space protected from ignition by gypsum wall board on one side and floor sheathing on the 

other). Protection from ignition can be accomplished with 1-1⁄2 -in.-thick (38 mm) mineral fiber 

insulation, 1⁄4-in.-thick (6.4 mm) wood structural panels, 3/8-in. (9.5 mm) particleboard, 1⁄4-in. (6.4 mm) 

hardboard, 3/8-in. (9.5 mm) gypsum board, or corrosion-resistant steel having a base metal thickness of 

0.016 in. (0.406 mm) 

Brick Veneer and the Air Space 

Harking back to “old-timer” practices, place sand at the bottom of the 1-in. air space to act as a bond 

break for mortar droppings and leave bricks out intermittently in the first course. After the veneer is 

completed, the sand and mortar droppings can be easily removed and the missing course brick mortared 

in. Head joints in the top and bottom course must be left clear for top and bottom venting of this space. 

Masons must also be aware of protecting the integrity of the XPS foam sheathing as they work, given its 

function as the wall’s drainage plane. Educate this trade with some building science basics about the 

impact of their work on building envelope performance. 

Brick Ties 

The two-piece adjustable ties are strongly recommended, given the 1-in. air space and foam insulation. 

See the Masonry Institute Technical Notes at www.brickinfo.org/pdfs/44b.pdf. 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow highperformance start-up procedures, such as those described on the BSC web site, 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf. Although 

this resource is primarily for refrigerant cooling systems, most of it applies to heat pumps. 

Conditioned Crawlspaces 

This assembly may require some local building code official "building science persuasion." See the 

Building Safety Journal article written by Nathan Yost of BSC

(www.buildingscience.com/resources/articles/24-27_Yost_for_author.pdf). 

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 3-6 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss. 
 

3-14

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Material Compatibility and Substitutions 

Exterior Sheathing 

The use of other common exterior sheathing materials—OSB, plywood or thin-profile structural 

sheathing (e.g., Thermo-ply®)—in this assembly must be done with recognition of the impact on heat and 

moisture transfer. 

Both OSB and plywood are more vapor permeable than rigid foam insulation, a good thing when the 

cavity-warming ability of the rigid insulation is lost. But keep in mind that behind the brick veneer (a 

reservoir cladding), the greater vapor permeability of the OSB or plywood heightens the importance of 

the continuous 1-in. air space. 

On the other hand, Thermo-ply® is less vapor permeable than rigid foam insulation and will pretty much 

eliminate drying potential to the exterior, a potential problem during the heating season, particularly the 

further north you build in this mixed climate. Builders in the northern half of this climate region who use 

Thermo-ply® as an exterior sheathing should ensure that controlled ventilation and occupant use of point 

exhaust fans keep the interior relative humidity below 30% during the peak of their heating season. 

Figure 3-6. Slider truss 
 

3-15

Rim Joist Blocking 

An alternative to this detail is to spray foam insulation on the rim joist to maintain air barrier continuity at 

this transition. 

Drainage Plane on Rigid Insulation 

An alternative to flashing, shiplapping, or sealing the XPS insulation for continuity of the drainage plane 

is to apply a housewrap to the outside of the insulation. The housewrap then becomes the continuous 

drainage plane. 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged as drying to the interior is important in mixed-humid climates. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Crawlspace Floor 

Ideally, the crawlspace floor would be a 4-in. gravel (free-draining, no fines) bed, polyethylene layer and 

"rat" (2-in. low strength cast concrete) slab, making this space more amenable to light storage and 

housing of HVAC equipment. The cost of this approach may outweigh the benefits for builders and 

buyers. If a concrete slab is cast, it should be placed directly on top of the vapor barrier. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, and kitchens, are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 
 

3-16

Building Profile #9. The Atlanta 

Foundation: Slab-on-grade Attic: Vented Cladding (1st): Vinyl siding 

Above Grade Walls: Wood frame Roof: Asphalt shingles Cladding (2nd): Vinyl siding 

Figure 3-7. Cross section of the Atlanta 
 

3-17

Building Science Details 

Ducts in Conditioned Space 

This building profile (Figure 3-7) is designed to accommodate HVAC equipment and ducts in the living 

space, with the equipment typically in an interior closet. HVAC ducts should not be run in exterior walls 

or the slab, locations that increase the potential for condensation and consequential air quality problems. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band Joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draft-stopping (wood blocking) and sealant/caulk, 

or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the air barrier. 

The air barrier detail on second-story band joists is important because it is inaccessible (covered by 

structural/finish floor and ceiling finish) after construction. The air barrier/thermal barrier detail is 

important on ground floor band joists because of the thermal bridge that can occur at the top of basement 

and crawlspace foundation walls (as the result of the air barrier and thermal barrier moving from the 

outside to the inside of the building envelope and termite inspection zones located at the top of basement 

and crawlspace foundation walls). Note that while fiberglass batts fulfill the requirement for protection 

from ignition in the open band joists, fiberglass batt material by itself cannot maintain the air barrier.

Attached Garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 3-8 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. For more details see www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls/insulation_sheathings.pdf). 

In the Mixed-Humid climate, roof and wall assemblies are best designed to dry to both the exterior and 

interior. This is not always possible when rigid exterior insulating sheathings are used because of their 

low vapor permeability. Accordingly, most drying occurs to the interior during the summer months. 

Therefore, interior vapor barriers should not be installed. Note that there is a difference between an 

interior vapor barrier and an interior vapor retarder. Because the interior finish is more vapor permeable 

than the exterior sheathing, the wall assembly for the “Atlanta” has greater drying potential to the interior 

(more cooling season drying potential) than to the exterior (less heating season drying potential; see 

Material Compatibility and Substitutions). 
 

3-18

Drainage Plane, Air Barrier, Vapor Control 

The drainage plane runs along the exterior surface of the foam sheathing. All vertical joints must be 

shiplapped, flashed, or sealed; all horizontal joints must be sealed or taped. 

This building profile has a continuous air barrier both on the interior walls (Airtight Drywall Approach on 

ceiling and walls, see www.buildingscience.com/housesthatwork/airsealing/default.htm) and on the 

exterior walls (the sealed rigid insulation). 

In mixed climates, wall and roof assemblies can be designed to dry primarily to the exterior (during the 

heating season), to the interior (during the cooling season), or in both directions. The last approach, with 

bi-directional drying potential, is generally preferred. For more detailed discussion of the three 

approaches, see the discussion of wall and roof design in the EEBA Builder’s Guides

(www.eeba.org/bookstore). 

Rough Opening Flashing 

Flashing must be installed at the plane of the XPS rigid insulation for drainage plane continuity. See 

Figure 3-9 and the EEBA Water Management Guide for sequential flashing details 

(www.eeba.org/bookstore). 

Advanced Framing 

Cross bracing (or other alternative for shear resistance) replaces structural sheathing in this wall 

assembly. Thermal performance and reduced drywall cracking are additional benefits of a comprehensive 

approach to advanced framing. See 

www.buildingscience.com/housesthatwork/advancedframing/default.htm for details. 

Figure 3-8. Creating a continuous air barrier 
 

3-19

Figure 3-9. Rough opening flashing 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult, if not impossible, to assess before 

completion of the structure—resultant confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-Slab Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 

practical, and the only capillary break between the slab and ground is the polyethylene vapor barrier. 

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate where the average monthly 

temperature for the coldest month of the year goes below 45°F. The rule of thumb that BSC uses is 1/4-in. 

of rigid insulation per 1,000 heating degree days (HDD). One inch of rigid insulation generally works 

well for this climate. In this climate, the heat loss through the slab perimeter is significant enough to 

warrant insulation. Note that the insulation system must comply with local codes for protection against 

insects, particularly termites. 
 

3-20

Climate-Specific Details 

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity 

is often the condition that requires higher ventilation rates. This can also depressurize the house causing 

loss of conditioned air. Generally, the area of the gable and soffit vents, combined with the leakage of the 

attic ceiling, is such that the fan pulls air not just from the exterior vent, but also from the conditioned 

space below. 

Mechanical Systems 

Heating and Cooling. We recommend a sealed combustion 90+ condensing gas furnace or an air-source 

heat pump, ENERGY STAR-rated or better (HSPF ≥ 8.0) (see 

www.energystar.gov/index.cfm?c=airsrc_heat.pr_as_heat_pumps, follow appropriate sizing procedures). 

For more detailed information, see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf.

Transfer Grilles. The single central return requires transfer grilles to provide an adequate return path 

and avoid pressurizing bedrooms, as shown in Figure 3-10. 

Figure 3-10. Transfer grille and jump ducts approaches 
 

3-21

Mechanical Ventilation. We recommend an intermittent central-fan-integrated supply, designed to 

provide the ASHRAE 62.2P recommended flow rate, with fan cycling control set to operate the central air 

handler 20 minutes every hour to provide ventilation air distribution and whole-house averaging of air 

quality and comfort conditions ($125 to $150). Include a normally closed motorized damper in the 

outside air duct with the AirCyclerTM FRV control (+$50 to $60) (Figure 3-11).

 

Interior Closet Configuration 

Figure 3-11. Mechanical ventilation for the “Atlanta” 
 

3-22

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the foundation. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials (see also 

Field Experience Notes below). 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 

Field Experience Notes 

Gable End Exterior Sheathing Detail 

Continuity of the drainage plane on gable end walls must be maintained. We recommend the detail shown 

in Figure 3-12. 

Figure 3-12. Gable end exterior sheathing detail 
 

3-23

Flashing Details 

Because the vinyl siding is a screened wall-cladding system, flashing details should be accomplished in 

the plane of drainage (building paper or house wrap), not the cladding. Do not caulk siding and do not 

rely on the "J"-channel as part of the drainage plane. In other words, never consider vinyl siding, 

aluminum siding (or any siding, for that matter) as the weather barrier. 

Termite Control 

Local codes and interpretations by building inspectors can make details involving rigid insulation 

difficult. We have found that building officials generally accept the flashing/fibercement board shown in 

the Building Profile and in Figure 3-13. 

Termite Flashing Continuity 

In order for the metal flashing to be effective, all joints must be epoxy-sealed (or welded) and the 

horizontal edge must be epoxy-sealed to the concrete. 

Air Sealing 

The hardest spots are not the fields but the margins/edges of assemblies. Air sealing at transitions such as 

rim joists and eaves requires either exacting blocking and caulk/sealant or spray foam insulation. Many 

Building America production builders have found the labor savings of spray foam insulating/air sealing to 

be well worth the added material cost. 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow high 

performance start-up procedures such as those described on the BSC web site 

(www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf) Although 

this resource is primarily for refrigerant cooling systems, most of it applies to heat pumps. 

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 3-13 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss. 

 

Figure 3-13. Flashing (left) and slider trusses (right) 
 

3-24

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Material Compatibility and Substitutions 

Exterior Sheathing 

The use of other common exterior sheathing materials—OSB, plywood or thin-profile structural 

sheathing (e.g., Thermo-ply®)—in this assembly must be done with recognition of the impact on heat and 

moisture transfer. 

Both OSB and plywood are more vapor permeable than rigid foam insulation, a good thing when the 

cavity-warming ability of the rigid insulation is lost. But keep in mind that behind the brick veneer (a 

reservoir cladding), the greater vapor permeability of the OSB or plywood heightens the importance of 

the continuous 1-in. air space. 

On the other hand, Thermo-ply® is less vapor permeable than rigid foam insulation and will pretty much 

eliminate drying potential to the exterior, a potential problem during the heating season, particularly the 

further north you build in this Mixed climate. Builders in the northern half of this climate region who use 

Thermo-ply® as an exterior sheathing should ensure that controlled ventilation and occupant use of point 

exhaust fans keep the interior relative humidity below 30% during the peak of their heating season. 

Rim Joist Blocking 

An alternative to this detail is to spray foam insulation on the rim joist to maintain air barrier continuity at 

this transition. 

Drainage Plane on Rigid Insulation 

An alternative to flashing, shiplapping, or sealing the XPS insulation for continuity of the drainage plane 

is to apply a housewrap to the outside of the insulation. The housewrap then becomes the continuous 

drainage plane. 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is important in mixed-humid climates. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Flooring 

Many finished flooring materials—either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example)—should only be installed over a slab with low 

w/c ratio (≈ 0.45 or less) or a slab allowed to dry (<0.3 grams/24hrs/ft2

) before installation of flooring. In 

general sheet vinyl flooring should be avoided. 
 

3-25

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, kitchens, are excellent candidates for 

non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 

L-channel Detail on Cladding at Base of Exterior Wall 

Any stop can be used at the bottom, exposed edge of the rigid insulation to prevent insect and rodent 

intrusion, as long as it does not interfere with the foam’s function as the drainage plane. 

XPS versus EPS Exterior Foundation Foam Insulation 

There are three rigid insulations appropriate for exterior use on foundations where the insulation will 

extend below grade and be in contact with soil conditions: 

XPS. This material’s density, impact resistance, and resistance to liquid penetration make it the preferred 

material. 

EPS. In areas where resistance to insects (especially termites and carpenter ants) is a desired or required 

characteristic of the insulation, EPS may be indicated because it is the only foam insulation that comes 

with a borate-treatment. However, water penetration and subsequent leaching of the borate treatment 

require a capillary break between the soil and the insulation. This is best accomplished with a gravel 

layer and Enkadrain® mat just exterior to the EPS insulation. 

Rigid Fiberglass. This is a great material for exterior insulation because of its drainability and resistance 

to insect degradation. However, availability of this material has been and remains the main constraint on 

its use.
 

3-26

Building Profile #10. The Louisville 

Foundation: Basement Attic: Vented cathedral ceiling Cladding: Vinyl siding 

Above Grade Walls: Wood frame Roof: Asphalt shingles 

Figure 3-14. Cross section of the Louisville 
 

3-27

Building Science Details 

Ducts in Conditioned Space 

This Building Profile (Figure 3-14) is designed to accommodate HVAC equipment and ducts in either the 

living space or in the basement. HVAC ducts should not be run in exterior walls. 

Cathedral Roof Assembly 

The continuous eave-to-ridge venting just to the inside of the structural roof deck serves to thermally 

decouple everything to the exterior of this air space from everything to its interior (sometimes called a 

“cold” roof). It is the continuity of the air space, the thermal barrier, and the air barrier that makes this 

roof assembly work. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists 

and between attached garages and living spaces. These are discussed below because they have proven to 

be a consistent challenge for builders. 

Band joist. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draft-stopping (wood blocking) sealant/caulk, or 

spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the air barrier. The 

air barrier detail on second-story band joists is important because it is inaccessible (covered by 

structural/finish floor and ceiling finish) after construction. The air barrier/thermal barrier detail is 

important on ground floor band joists because of the thermal bridge that can occur at the top of basement 

and crawlspace foundation walls (as the result of the air barrier and thermal barrier moving from the 

outside to the inside of the building envelope and termite inspection zones located at the top of basement 

and crawlspace foundation walls). Note that while fiberglass batts fulfill the requirement for protection 

from ignition in the open band joists, fiberglass batt material by itself cannot maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 3-15 for details in terms of using 

sealants and rigid insulation to create a continuous air barrier between the attached garage and living 

space. For more details see www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Figure 3-15. Creating a continuous air barrier 
 

3-28

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls,insulation_sheatings.pdf). 

In mixed-humid climates, roof and wall assemblies are best designed to dry to both the exterior and 

interior. This is not always possible when rigid exterior insulating sheathings are used because of their 

low vapor permeability. Accordingly, most drying occurs to the interior during the summer months. 

Therefore, interior vapor barriers should not be installed. Note that there is a difference between an 

interior vapor barrier and an interior vapor retarder (see Material Compatibility and Substitutions). 

Drainage Plane, Air Barrier, Vapor Control 

The drainage plane runs along the exterior surface of the foam sheathing. All vertical joints must be 

shiplapped, flashed, or sealed; all horizontal joints must be sealed or taped. 

This building profile has a continuous air barrier on both the interior walls (Airtight Drywall Approach on 

ceiling and walls, see www.buildingscience.com/housesthatwork/airsealing/default.htm) and the exterior 

walls (the sealed rigid insulation). 

In mixed climates, wall and roof assemblies can be designed to dry primarily to the exterior (during the 

heating season), to the interior (during the cooling season) or in both directions. This last approach, with 

bi-directional drying potential, is generally preferred. For more detailed discussion of the three 

approaches, see the discussion of wall and roof design in the EEBA Builder’s Guides

(www.eeba.org/bookstore). Because the permeability of the latex-painted gypsum board is greater than 

that of the XPS rigid insulation, the wall assembly in the “Louisville” is designed to dry more to the 

interior. 

Rough Opening Flashing 

Flashing is always installed in the plane of drainage for continuity. This means that when a different 

material or “layer” makes up the drainage plane, window flashing details must move accordingly. See 

Figure 3-16 and the EEBA Water Management Guide for sequential flashing details 

(www.eeba.org/bookstore). 
 

3-29

Figure 3-16. Rough opening flashing 

Advanced Framing 

The use of non-structural sheathing in this wall assembly means that cross bracing or some alternative for 

shear resistance is required. The reduced use of lumber, improved thermal performance and reduced 

drywall cracking are benefits of a comprehensive approach to advanced framing. See 

www.buildingscience.com/housesthatwork/advancedframing/default.htm for details. 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab. Using sill sealer on all walls maintains the same wall height. 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult if not impossible to assess before 

completion of the structure—resultant confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-slab Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 

practical and the only capillary break between the slab and ground is the polyethylene vapor barrier. 
 

3-30

Thermal Barrier 

Cavity-warming exterior rigid insulation is important in this climate where the average monthly 

temperature for the coldest month of the year goes below 45°F. The rule of thumb that BSC uses is 1⁄4 in. 

of rigid insulation per 1,000 heating degree days (HDD). One inch of rigid insulation generally works 

well for this climate. The heat loss through the basement walls is significant enough to warrant insulation. 

Note that the insulation must comply with local codes for protection against ignition. 

Basement and Slab Insulation 

Although the basement walls and basement slab as shown clearly go beyond what is required by any code 

for this climate, this assembly assumes that the basement either is or will become a living space. It is not, 

however, the energy performance that is driving this design, but rather occupant comfort, dust mite 

control, and reduced potential for moisture problems that justifies the added cost of the assembly’s 

insulation. See the BSC technical resource “Basement Insulation Systems” for other basement wall 

assemblies that work well 

(www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf). 

Foundation Sealant Details 

Note that the inside bead of sealant or caulk is an air sealing detail. The sealant between the two sheets of 

rigid insulation is actually a seal against insect and soil gas infiltration—this calls for a chemical bonding 

that can be accomplished with two-part urethane. 

Climate-Specific Details 

Mechanical Systems 

Heating and Cooling. We recommend a sealed combustion gas furnace, for both energy efficiency and 

health/safety reasons, with the unit located inside conditioned space. (The “Louisville”— which 

encounters just under 5,000 heating degree days—is just about at the margin of heat pump winter-time 

efficiency, hence the recommendation for a gas heating and separate electric cooling system). We also 

recommend a minimum 12 SEER A/C unit, for energy efficient management of sensible load. Follow 

appropriate sizing procedures, using the guidelines on the BSC web site for more detailed information 

(www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf). 

Transfer Grilles. The single central return requires transfer grilles or jump ducts to provide an adequate 

return air path and avoid pressurizing bedrooms, as shown in Figure 3-17. 
 

3-31

Figure 3-17. Transfer grille and jump duct approaches 

Mechanical Ventilation. We recommend an intermittent central-fan-integrated supply system, designed 

to provide the ASHRAE 62.2P recommended flow rate, with fan cycling control set to operate the central 

air handler 20 minutes every hour to provide ventilation air distribution and whole-house averaging of air 

quality and comfort conditions ($125 to $150). Include a normally closed motorized damper in the 

outside air duct with the AirCyclerTM FRV control (+$50 to $60) (Figure 3-18).
 

3-32

 

Basement Configuration 

Figure 3-18. Mechanical ventilation in the “Louisville” 
 

3-33

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building. Maintain any 

termite inspection zone on the foundation. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building. Make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 

Field Experience Notes 

Termite Control 

Local codes and interpretations by building inspectors can make details involving rigid insulation 

difficult. Even though foam used on the interior of a basement wall is exempt from typical code 

restrictions on the use of rigid foam insulation, an inspection zone at the top of the insulated and studdedout wall could be incorporated without unduly comprising the thermal barrier at this location. 

Air Sealing 

The air sealing details in the basement and at the first floor rim joist do not include any foam insulation or 

other materials that require protection from ignition. Note that if foam insulation were used at these 

locations, it could not be left exposed, according to the language used in many building codes. 

Flashing Details 

Because the vinyl siding is a screened wall cladding system, flashing details should be accomplished in 

the plane of drainage (building paper or house wrap), not the cladding. Do not caulk siding and do not 

rely on "J"-channel as part of the drainage plane. In other words, never consider vinyl siding, aluminum 

siding (or any siding, for that matter) as the weather barrier. 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow highperformance start-up procedures such as those described on the BSC web site 

(www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf). Although 

this resource is primarily for refrigerant cooling systems, most of it applies to heat pumps as well. 

Energy Trusses 

A number of different truss configurations yield greater depth at the heel, but they vary quite a bit in cost. 

The truss shown in Figure 3-19 (sometimes called a “slider” truss) has proven to be among the most costcompetitive. And, of course, the pitch of the roof affects just how much insulation you can get at this 

location, regardless of the type of truss. 
 

3-34

Figure 3-19. Slider truss 

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Stepped Foundation Insulation Detail 

Maintaining thermal barrier continuity in stepped foundations has proven easy to neglect. The detail in 

Figure 3-20 shows how the rigid foam needs to be cut and placed. 

Cathedral Ceiling Interior Finish 

To maintain air barrier continuity at the top of the exterior walls, a break with tradition is required. The 

wall gypsum board must go up before the ceiling board. Furring strips (1 x 4) secured through the foam 

insulation to the roof framing make hanging the ceiling a lot less painful. Using 2 x 4 rather than 1 x 4 

furring provides the required space for shallow electrical boxes in the ceiling (i.e., the continuous thermal 

barrier and air barrier of the ceiling rigid insulation is maintained). 
 

3-35

Figure 3-20. Stepped foundation insulation detail 

Material Compatibility and Substitutions 

Exterior Sheathing 

The use of other common exterior sheathing materials—OSB, plywood, or thin-profile structural 

sheathing (e.g., Thermo-ply®)—in this assembly must be done with recognition of the impact on heat and 

moisture transfer. 

Both OSB and plywood are more vapor permeable than rigid foam insulation, a good thing when the 

cavity-warming ability of the rigid insulation is lost. But keep in mind that behind any reservoir cladding, 

the greater vapor permeability of the OSB or plywood would make a continuous 1-in. air space essential. 

On the other hand, Thermo-ply® is less vapor permeable than rigid foam insulation and will pretty much 

eliminate drying potential to the exterior. This presents a potential problem during the heating season, 

particularly the further north you build in this mixed climate. Builders in the northern half of this climate 

region who use Thermo-ply® as an exterior sheathing should ensure that controlled ventilation and 

occupant use of point exhaust fans keep the interior relative humidity below 30% during the peak of their 

heating season. 

Rim Joist Blocking 

An alternative to this detail is to spray foam insulation on the rim joist to maintain air barrier continuity at 

this transition. 
 

3-36

Drainage Plane on Rigid Insulation 

An alternative to flashing, shiplapping, or sealing the XPS insulation for continuity of the drainage plane 

is to apply a housewrap to the outside of the insulation. The housewrap then becomes the continuous 

drainage plane. 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is important in mixed-humid climates. 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that has relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

L-channel Detail on Cladding at Base of Exterior Wall 

Any stop can be used at the bottom, exposed edge of the rigid insulation to prevent insect and rodent 

intrusion, as long as it does not interfere with the foam’s function as the drainage plane. 

Cast Concrete Foundation Walls 

If block is used instead of cast concrete for foundation walls, the bond beam becomes essential to 

maintain air barrier continuity at the top of the block wall. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, and kitchens, are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 

Flooring 

Many finished flooring materials—either because of their impermeability (sheet vinyl, for example) or 

sensitivity to moisture (wood strip flooring, for example)—should only be installed over a slab with low 

w/c ratio (≈ 0.45 or less) or a slab allowed to dry (<0.3 grams/24hrs/ft2

) before installation of flooring. In 

general, sheet vinyl flooring should be avoided. 
 

4-1

IV. Houses That Work for Hot-Dry/Mixed-Dry Climates 

Introduction

Hot-Dry and Mixed-Dry climates share an important climatic feature: precipitation is less than 20 in. 

annually. There is an important climatic difference, however, between the two: Hot-Dry climates do not 

have a monthly average temperature that drops below 45°F, while Mixed-Dry climates do. The 

significance of this threshold will become evident in the following sections. 

Moisture is, in general, not as much of a problem in these climates as the others. Even if the house gets 

wet, the dry (and often hot) conditions will usually quickly dry it out. Nevertheless, problems can occur 

when even a brief period of heavy rain deposits several inches of water onto a poorly designed or 

constructed building. Improper irrigation can also replace precipitation as a moisture source, and leaks 

can be expected to happen. If water collects in an area that cannot quickly dry, deterioration of the 

building can occur. 

Intense solar radiation is a problem in these climates, specifically in terms of managing the cooling load 

on the building and preventing ultra-violet degradation of many building materials, such as wood, paint, 

and plastics. An associated phenomenon (the lack of precipitation) means managing the fire risk of the 

structure is especially important, particularly in terms of exterior claddings and landscaping. 

The coldest-month-of-the-year average temperature threshold of 45°F is determinant in both roof and wall 

assemblies. It is critical for building design because the dew point temperature of air at 70°F and 35% 

relative humidity (RH) is approximately 40°F. Consequently, interior air at 70°F and 35% RH (which is a 

realistic condition in a tightly constructed house) will condense on a surface that is 40°F or cooler. The 

amount of water that will condense on the interior surface of the exterior sheathing (the first condensing 

surface) is a function of the dew point temperature of the interior air, the amount of air leakage into the 

wall, and the vapor permeability of the materials in the wall. Small amounts of condensation will not be a 

problem if the wall allows drying to the exterior. Adding a 5°F “buffer” or safety factor to the interior 

design temperature/humidity dew point (40°F dew point, 70°F, 35% RH) yields the 45°F monthly 

threshold temperature. 

Using a thin 1-in. layer of insulating sheathing (R-4) will warm the temperature of the first condensing 

surface, decreasing the chance that significant condensation will ever occur in the wall assembly. For this 

reason, we recommend an insulating sheathing in Mixed-Dry climates. 

We have chosen three Building Profiles that we think represent building science and regional building 

practices in Hot-Dry and Mixed-Dry climates: 

The “Albuquerque” ―one-story, stick-framed, slab-on-grade, stucco exterior, vented attic, 

asphalt shingle roof (with information provided for a optional conditioned crawlspace). 

This Building Profile is suitable for a Mixed-Dry climate (Figure 4-1). 

The “Sacramento” ―two-story, stick-framed, post-tensioned slab-on-grade, first story with 

fiber-cement siding/second story with stucco, vented attic, tile roof (with information 

provided for a one-story with unvented, conditioned attic). This Building Profile is 

suitable for a Hot-Dry climate (Figure 4-8). 

The “Tucson” ―one-story, stick-framed, slab-on-grade, stucco exterior, flat ceiling (no attic), 

membrane roof. This Building Profile is also suitable for a Hot-Dry climate, with 

information provided for moving this building to a mixed-dry climate (Figure 4-15). 
 

4-2

A substantial amount of repetition is present in these Building Profiles, but is necessary in order to 

provide comprehensive, stand-alone, examples of performance packages that achieve 40% energy savings 

while maintaining or improving quality and durability. 

For information about a production builder from each of these two climate regions, see 

www.buildingscience.com/buildingamerica/casestudies/default.htm. These case studies explore builder 

experience with the BA program and discuss the reasons for the specific design and construction details 

that Artistic Homes and Pulte Homes employ. To see detailed drawings on Advanced Framing and Air 

Sealing Techniques, go to www.buildingscience.com/housesthatwork/advancedframing/default.htm. 

Additional information on construction methods and alternative designs is included in the Builder's Guide 

for Hot-Dry and Mixed-Dry Climates (www.eeba.org/bookstore). 

Building America Best Practices for Hot-Dry/Mixed-Dry Climates 

High performance Building America homes in hot-dry/mixed-dry climates are faced with a significant 

heating season (up to 5400 heating degree days, and for mixed-dry climates, monthly average outdoor 

temperatures dropping below 45oF during winter months), as well as a significant cooling season. 

The following Best Practices are based on our Building America Performance Targets 

(www.buildingscience.com/buildingamerica/targets.htm) and are reflected in the three Building Profiles: 

the “Albuquerque,” the “Tucson,” and the “Sacramento.” All climate-specific best practices are identified 

with a bolded and bracketed [HD-MD]. 

Process: Building Design, Systems Engineering, and Commissioning 

Design for Energy Performance 

Energy performance for space conditioning and hot water is 40% better than the 1995 Model Energy 

Code base case house (i.e., equal to 10% better than ENERGY STAR performance requirements). 

Systems Engineering 

Design the structure using advanced framing methods (see 

www.buildingscience.com/housesthatwork/advancedframing/default.htm or 

www.buildingscience.com/resources/presentations/advanced_framing.pdf). 

Design the structure to accommodate the most efficient duct distribution system that places all ducts and 

air-handling equipment within conditioned space (see 

www.buildingscience.com/resources/misc/wood_efficiency.pdf; specifically Figure 3 and page 5). 

Design and detail the structure for durability, in terms of wall and roof assembly drying potential, 

continuous drainage plane, and continuous thermal boundary that clearly defines the conditioned space 

(see Building Profiles). [HD-MD] 

Commissioning: Performance Testing 

Air leakage (determined by blower door depressurization testing) should be less than 2.5 in.2/100 ft2 

surface area leakage ratio (CGSB, calculated at a 10-Pa pressure differential); or 1.25 in.2/100 ft2 leakage 

ratio (ASTM, calculated at a 4-a pressure differential); or 0.25 cfm/ ft2 of building envelope surface area 

at a 50-Pa air pressure differential. If the house is divided into multiple conditioned zones, such as a 

conditioned attic or conditioned crawl space, the blower door requirement must be met with the access to 

the space open, connecting the zones. 

Ductwork leakage to the exterior for ducts distributing conditioned air should be limited to 5% of the total 

air-handling system rated air flow at high speed (nominal 400 cfm per ton) determined by pressurization 
 

4-3

testing at 25 Pa. Two acceptable compliance mechanisms are (1) test duct leakage to outside at finish 

stage, or (2) test total duct leakage at duct rough-in stage. 

Forced-air systems that distribute air for heating and cooling should be designed to supply airflow to all 

conditioned spaces and zones (bedrooms, hallways, basements), as well as to provide a return path from 

all conditioned spaces or zones. Interzonal air pressure differences, when doors are closed, should be 

limited to 3 Pa. This is typically achieved by installing properly sized transfer grilles or jump ducts (see 

www.buildingscience.com/resources/mechanical/transfer_grille_detail.pdf and 

www.buildingscience.com/resources/mechanical/transfer_grille_sizing_charts.pdf). 

Mechanical ventilation system airflow should be tested during commissioning of the building. 

Testing of the house should be completed as part of the commissioning process. The SNAPSHOT form 

is available for download as a convenient way to record the testing information (see 

www.buildingscience.com/buildingamerica/snapshot_form.pdf). Instructions for completing the form are 

also available (see www.buildingscience.com/buildingamerica/snapshot_instructions.pdf). Unique or 

custom house plans should each be tested. In a production setting, each model type (i.e., floor plan) 

should be tested until two consecutive houses of this model type meet testing requirements. At that point, 

testing on the same model type can be reduced to a sampling rate of one in seven (i.e., one test, with six 

"referenced" houses). Small additions to a floor plan (e.g., bay window, conversion of den to bedroom) 

should be considered the same model type; major changes (e.g., bonus room over the garage, conversion 

of garage into a hobby room, etc.) should be considered a separate model type. 

Site: Drainage, Pest Control, and Landscaping 

Drainage 

Grading and landscaping shall be planned for movement of building run-off away from the home and its 

foundation, with roof drainage directed at least 3 ft beyond the building, and a surface grade of at least 

5% maintained for at least 10 ft around and away from the entire structure. 

Pest Control 

Based on local code and Termite Infestation Probability (TIP) maps, use environmentally appropriate 

termite treatments, bait systems, and treated building materials that are near or have ground contact (see 

www.uky.edu/Agriculture/Entomology/entfacts/) [HD-MD] 

Landscaping 

Plantings should be held back as much as 3 ft and no less than 18 in. from the finished structure, with any 

supporting irrigation directed away from the finished structure. Decorative ground cover—mulch or pea 

stone, for example—should be thinned to no more than 2 in. for the first 18 in. from the finished structure 

(see Building Profiles). [HD-MD] 

Foundation: Moisture Control and Energy Performance 

Moisture Control 

The building foundation shall be designed and constructed to prevent the entry of moisture and other soil 

gases (see Building Profiles). [HD-MD] 

Slabs require a 6-mil polyethylene vapor barrier directly beneath the concrete or an equivalent approach 

(such as rigid insulation) that accomplishes vapor and capillary control for the slab. The vapor barrier 

must continuously wrap the slab as well as the grade beam. 

Sub-slab drainage should consist of a granular capillary break directly beneath the slab vapor retarder. 
 

4-4

Use radon resistant construction practices as described on the EPA radon control web site 

(www.epa.gov/iaq/radon/construc.html).

Energy Performance 

Slabs in mixed-dry climates should be insulated at the perimeter (energy modeling reveals significant heat 

loss at this portion of the building envelope during the heating season). Consider the use of borate-treated 

rigid insulation on the slab perimeter. In hot-dry climates, slabs do not require insulation (see Building 

Profiles and photo details at www.buildingscience.com/buildingamerica/casestudies/fairburn.htm). [HDMD]

Envelope: Moisture Control and Energy Performance 

Moisture Control 

Water management. Roof and wall assemblies must contain elements that provide drainage in a 

continuous manner over the entire surface area of the building enclosure, including lapped flashing 

systems at all penetrations. See the Building Profiles and the EEBA Water Management Guide for 

specific details for various wall assemblies. [HD-MD]

Vapor management. Roof and wall assemblies must contain elements that, individually and in 

combination, permit drying of interstitial spaces. See the Building Profiles. [HD-MD]

Energy Performance 

Air leakage. The exterior air flow retarder (e.g., foam sheathing) or interior air flow retarder (e.g., 

gypsum board) is sealed to the slab and frame walls (Airtight Drywall Approach). For details of the ADA 

for the interior air flow retarder, see www.buildingscience.com/housesthatwork/airsealing/default.htm. 

Windows. We recommend windows with U-factor 0.35 or lower and SHGC (solar heat gain coefficient) 

0.35 or lower. [HD-MD]

Mechanicals / Electrical / Plumbing 

Systems Engineering

HVAC system design, both equipment and duct, should be done as an integral part of the architectural 

design process.

HVAC system sizing should follow ACCA Manual J, and duct sizing should follow Manual D (see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf).

Mechanical ventilation should be an integral part of the HVAC system design (see the Building Profiles 

and www.buildingscience.com/resources/mechanical/advanced_space_conditioning.pdf.). [HD-MD]

Energy Performance

Air conditioner or heat pump should be installed according to best practices (see 

www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf.).

Major appliances should meet high-energy efficiency standards using current appliance ratings. Only 

those appliances in the top one-third of the DOE Energy Guide rating scale should be selected (for details, 

see www.eren.doe.gov/consumerinfo/energy_savers/appliances.html).

Occupant Health and Safety

Base rate ventilation: Controlled mechanical ventilation per ASHRAE Standard 62.2. 
 

4-5

Spot ventilation: intermittent spot ventilation of 100 cfm should be provided for each kitchen; all kitchen 

range hoods must be vented to the outside (no recirculating hoods). Intermittent spot ventilation of 50 

cfm, or continuous ventilation of 20 cfm when the building is occupied, should be provided for each 

washroom/bathroom.

All combustion appliances in the conditioned space must be sealed combustion or power vented. 

Specifically, any furnace inside conditioned space should be a sealed-combustion 90%+ unit. Any water 

heater inside conditioned space should be power vented or power-direct vented. Designs that incorporate 

passive-combustion air-supply openings or outdoor supply air ducts not directly connected to the 

appliance should be avoided.

Provide filtration systems for forced-air systems that provide a minimum atmospheric dust-spot efficiency 

of 30% or MERV of 6 or higher.

Indoor humidity should be maintained in the range of 25% to 60% by controlled mechanical ventilation, 

mechanical cooling, or dehumidification (see 

www.buildingscience.com/resources/moisture/relative_humidity_0402.pdf).

Carbon-monoxide detectors (hard-wired units) shall be installed (at one per every approximate 1000 ft2

) 

in any house containing combustion appliances and/or an attached garage.

Information relating to the safe, healthy, comfortable operation and maintenance of the building and 

systems that provide control over space conditioning, hot water, or lighting energy use shall be provided 

to occupants.

Envelope/Mechanicals Management 

Plumbing. No plumbing in the exterior walls. Air seal around plumbing penetrations in the pressure 

boundary (air barrier) such as rim (band) joist or ceiling. 

Electrical. Seal around wires penetrating the air barrier or pressure boundary. 
 

4-6

Building Profile #11. The Albuquerque 

Foundation: Slab-on-grade Attic: Unconditioned Cladding: Stucco 

Above Grade Wall: Wood frame Roof: Asphalt shingles 

Figure 4-1. Cross section of the Albuquerque 
 

4-7

Building Science Details 

Ducts in Conditioned Space 

This building profile is designed to accommodate HVAC equipment and ducts in the living space, 

specifically in dropped soffits where design and layout permit. HVAC ducts should not be run in exterior 

walls or the slab. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such between 

attached garages and living spaces. 

Attached Garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 4-2 and 

www.buildingscience.com/housesthatwork/airsealing/default.htm for details in terms of using sealants 

and rigid insulation to create a continuous air barrier between the attached garage and living space. 

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information

(www.buildingscience.com/resoruces/walls/insulation_sheathings.pdf). This wall assembly permits 

drying to both the interior and the exterior (depending on the selection of exterior sheathing). For further 

information, see the Building Materials Property Table (Table 1). 

Drainage Plane, Air Barrier, and Vapor Control 

The drainage plane in this wall assembly is the Dupont StuccoWrap® weatherlapped onto the OSB structural sheathing 

(the building paper just exterior to the drainage plane is the bond break for the stucco cladding). An annual precipitation 

of 8 in. (30-year average for Albuquerque) means that a face-sealed stucco cladding can work, but this system is 

designed with a drainage plane as a “belt and suspenders” approach for long-term durability. 

Figure 4-2. Continuous air barrier 
 

4-8

The air barrier is the interior gypsum board installed using the Airtight Drywall approach (see Air Sealing 

Details). 

The wall and roof assemblies in this building are “flow-through” assemblies, with moderate to high 

relative vapor permeability in all components of the wall and roof. This bi-directional drying is the 

preferred approach in mixed-dry climates. 

Rough Opening Flashing 

Window and door flashing details are wall assembly or cladding specific and depend on whether the 

windows are installed before or after the drainage plane. Refer to the EEBA Water Management Guide for 

more information (www.eeba.org/bookstore). 

Advanced Framing 

This wall assembly employs all of the advanced framing methods except alternative shear resistance 

(structural sheathing is used). For advanced framing details, see

www.buildingscience.com/housesthatwork/advancedframing/default.htm. 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed-cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains the same wall height). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult, if not impossible, to assess before 

completion of the structure—residual confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides), methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-Slab Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not a 

practical solution, and the only capillary break between the slab and ground is the polyethylene vapor 

barrier. 

Thermal barrier 

In general, we recommend cavity-warming exterior rigid insulation in climates where the average 

monthly temperature for the coldest month of the year goes below 45°F. But in this assembly, the 

excellent drying potential of the “flow-through” wall assembly is achieved in part by the absence of any 

rigid insulation with relatively low vapor permeability. Because mixed-dry climates have significant, but 

not extreme, periods of winter temperatures below 45°F, either approach to thermal performance/vapor 

control works well. 

In Albuquerque, the heat loss through the slab perimeter is significant enough to warrant slab-edge 

insulation. See Termite Control under Field Experience Notes for the details. 

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity 

is often the condition that requires higher ventilation rates. They can also depressurize the house causing 
 

4-9

loss of conditioned air. Generally, the area of the gable and soffit vents, combined with the leakage of the 

attic ceiling, is such that the fan pulls air not just from the exterior vent, but also from the conditioned 

space below.

Climate-Specific Details 

Mechanical Systems 

Heating. Our recommendation to high-performance production homebuilders in mixed-dry climates is to 

use combination space/domestic water heating systems (i.e., “combo” units), but this recommendation 

comes heavily qualified. For details, see Figure 4-3 and the BSC technical resource “Combo Space/Water 

Heating Systems: ‘Duo Diligence’,” 

(www.buildingscience.com/resources/mechanical/combo_systems.pdf). 

Cooling. Evaporative cooling is prevalent in Mixed-Dry Climates. We recommend refrigerant cooling in 

high-performance homes in this climate region for three reasons: 

1. Refrigerant cooling permits year-round controlled ventilation; evaporative cooling does not. 

2. Evaporative cooling can be prone to moisture and indoor air quality problems without frequent 

and diligent system maintenance. Refrigerant cooling is not. 

3. While there can be a slight energy penalty with refrigerant cooling in comparison to evaporative 

cooling, this penalty must be balanced against the year-round comfort provided by refrigerant 

cooling (evaporative cooling has difficulty supplying comfort in high humidity situations) and the 

substantial water savings associated with refrigerant cooling (a growing issue in mixed-dry 

climates). 

Follow appropriate sizing procedures. For more detailed information, see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

Transfer Grilles. The single central return requires transfer grilles to provide an adequate return path 

and avoid pressurizing bedrooms, as shown in Figure 4-4. Appropriate sizing for ducts, including these 

pressure relief methods, can be found at 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

Figure 4-3. Combo heating system 
 

4-10

 

Figure 4-4. Ducting, transfer grilles, and interior closet configuration 
 

4-11

Controlled Mechanical Ventilation. We recommend an intermittent central-fan integrated supply, 

designed to provide the ASHRAE 62.2P recommended flow rate, with fan-cycling controls set to operate 

the central air handlers 20 minutes every hour to provide ventilation air distribution and whole-house 

averaging of air quality and comfort conditions (installed cost: $125 to $150). Include a normally closed 

motorized damper in the outside duct with the AirCyclerTM FRV control (installed cost: $50 to $60). This 

ventilation system is illustrated in Figure 4-4.

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2-in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 

Landscaping for wildfire control 

Keeping woody materials of any type, living or otherwise, away from the building is good practice in dry 

climates where wildfires present a significant risk. 

Field Experience Notes 

Termite Control 

Local codes and interpretations by building inspectors can make details involving slab insulation difficult. 

We have found that building officials accept the flashing/FiberCement board shown in the Building 

Profile and in Figure 4-5. 

Figure 4-5. Flashing with FiberCement board 
 

4-12

Termite Flashing Continuity 

In order for the metal flashing to be effective, all joints must be epoxy-sealed (or welded) and the 

horizontal edge must be epoxy-sealed to the concrete. 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow high 

-performance start-up procedures such as those described on the BSC web site 

(www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf). 

In dry climates, it is generally a good idea to set up the air distribution fan to run a little longer at the end 

of each cycle to bump up the sensible efficiency. 

Location of HVAC Outdoor Unit 

It’s tempting to put the condenser right on the roof where evaporative cooling units are typically located, 

particularly when lot lines are very tight. We do not recommend a rooftop location of the condenser for 

several reasons: it makes even routine maintenance more difficult, it puts the unit at what is most likely 

the hottest spot on the entire property, and it introduces more roof penetrations. 

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 4-6 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss.

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf. 

Figure 4-6. Slider truss 
 

4-13

Slab 

In dry climates, it is quite common for builders to use a sand layer in between the polyethylene sheet 

(“poly”) and the cast concrete to prevent differential drying and cracking problems. This moistureholding layer should never be placed between the poly and concrete. Differential drying and subsequent 

cracking should be handled with a low-water-content concrete and wetted burlap covering. For more 

information, see www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm.

Keeping Ducts in Conditioned Space 

Many builders in Mixed-Dry climates build in areas where the prevailing architecture can make locating 

all ducts and HVAC equipment in conditioned space more than a bit challenging, particularly when 

moving from smaller, more affordable homes to more architecturally complex upgrade homes. Moving 

from slab-on-grade to a conditioned crawlspace is one way to maintain the local architectural style while 

improving performance. The detail in Figure 4-7 shows how one Mixed-Dry climate Building America 

production builder used a conditioned crawlspace to move ducts into conditioned space cost-efficiently, 

in terms of builder construction costs, homeowner operating costs, and maintained energy and comfort. 

The following section describes some points to remember when making the change from slab-on-grade to 

a conditioned crawlspace. 

Conditioned crawlspace. Conditioning of the crawlspace means that this space must be constructed 

much like a living space; it must be supplied by the HVAC system and have a transfer grille to return air 

back to the HVAC system through the living space. The supply air should be directed horizontally across 

the crawlspace with good enough "throw" to provide some mixing, not directed down at the floor. Sizing 

of the supply air should be about 5% of the conditioned crawlspace floor area (for example: 0.05 

cfm/ft2

*1600 ft2 = 80 cfm for a 1600 ft2 conditioned crawlspace). A single 6-in.-diameter supply duct 

typically suffices. Transfer air should go back to the central area of the living space above the crawlspace. 

Two grilles (10 in. by 4 in.) on opposite sides of the crawlspace are usually sufficient. The transfer area 

should be calculated in the same manner as for closed bedrooms connecting to hallways, using the 3-Pa 

pressure difference limit. Some form of mechanical moisture control for the crawlspace is necessary. We 

recommend one of the following approaches: 

Figure 4-7. Conditioned crawlspace 
 

4-14

1. A controlled ventilation strategy using the intermittent central fan-integrated supply, which 

provides both mixing and moisture removal for the crawlspace as well as the house 

2. A stand-alone dehumidifier installed in the crawlspace 

3. A continuously operating crawlspace exhaust fan with make-up air extracted from the house. 

In the “Albuquerque,” the rigid insulation is applied to the interior face of the exterior foundation walls. 

Moisture control is important to proper performance, in particular the vapor barrier ground cover on the 

floor of the crawlspace. The vapor barrier must be continuous and sealed to the perimeter wall and any 

supporting piers. This crawlspace assembly may require discussion with the local building code official. 

See the Building Safety Journal article written by Nathan Yost of BSC: 

www.buildingscience.com/resources/articles/24-27_Yost_for_author.pdf.

Crawlspace Access 

The preferred location for crawlspace access is through the subfloor; any access through the perimeter 

wall must be air sealed and insulated. 

Air Sealing 

Most codes can be interpreted to require only protection of foam from “ignition” in crawlspaces (“where 

entry is made only for service of utilities”). The same applies to foam at the rim joist (this is an interstitial 

space protected from ignition by gypsum wall board on one side and floor sheathing on the other). 

Protection from ignition can be accomplished with 11⁄2 -in.-thick (38 mm) mineral fiber insulation, 1/4-

in.-thick (6.4 mm) wood structural panels, 3/8-in. (9.5 mm) particleboard, 1⁄4-in. (6.4 mm) hardboard, 3/8-

in. (9.5 mm) gypsum board, or corrosion-resistant steel having a base metal thickness of 0.016 in. (0.406 

mm).

Layout and Floor Framing 

The introduction of floor framing means that floor plans and dimensions that worked well for a slab may 

no longer be efficient in terms of wood use. Be prepared to investigate the relationship between design 

and efficient wood use. For more information, see “Using Wood Efficiently: From Optimizing Design to 

Minimizing the Dumpster” (www.buildingscience.com/resources/misc/wood_efficiency.pdf).

Material Compatibility and Substitutions 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is important in mixed climates. 

Building Papers with Stucco 

There must always be two separate components here: the bond break material and the drainage plane. 

Although StuccoWrap® is advertised as both a drainage plane material and the layer receiving the stucco, 

these two components should never be combined or reversed. 

Exterior Sheathing Materials 

In this assembly, the use of a reservoir cladding suggests that a moisture-sensitive material such as 

fiberboard should not be used. On the other hand, the lack of cavity-warming exterior insulation means 

that an impermeable sheathing such as thin-profile structural sheathing (e.g., Thermo-ply®, Energy Brace) 

should not be used. Plywood is an acceptable substitution for OSB in this wall assembly. For more 

information, see the Building Materials Property Table (Table 1) or “Insulations, Sheathings, and Vapor 

Diffusion Retarders” (www.buildingscience.com/resources/walls/insulation_sheathings.pdf).
 

4-15

Cavity Insulation Materials 

Acceptable cavity insulation includes any that have relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Flooring 

Because curing concrete releases significant moisture for several months after being cast, we recommend 

that a low w/c concrete ratio (<0.45) be used to protect the integrity of finished flooring. We also 

recommend that vinyl flooring not be installed over a concrete slab. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, and kitchens, are excellent candidates 

for non-paper-faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 

XPS Versus EPS Exterior Foundation Foam Insulation 

There are three rigid insulations appropriate for exterior use on foundations where the insulation will 

extend below grade and be in contact with soil conditions: 

XPS. This material’s density, impact resistance, and resistance to liquid penetration make it the 

preferred material. 

EPS. In areas where resistance to insects (especially termites and carpenter ants) is a desired or required 

characteristic of the insulation, EPS may be indicated because it is the only foam insulation that comes 

with a borate-treatment. However, water penetration and subsequent leaching of the borate treatment 

require a capillary break between the soil and the insulation. This is best accomplished with a gravel layer 

or an Enkadrain® mat just exterior to the EPS insulation. 

Rigid Fiberglass. This is a great material for exterior insulation because of its drainability and resistance 

to insect degradation. However, availability of this material has been and remains the main constraint on 

its use.
 

4-16

Building Profile #12. The Sacramento 

Foundation: Post-tensioned slab-on-grade Attic: Unconditioned Cladding (1st floor): Fiber cement siding 

Above Grade Walls: Wood frame Roof: Tile Cladding (2nd floor): Stucco 

Figure 4-8. Cross section of the Sacramento 
 

4-17

Building Science Details 

Ducts in Conditioned Space 

This building profile is designed to accommodate HVAC equipment and ducts in the living space, 

specifically with the air handler in an interior closet and the ducts in the second floor framing, resulting in 

a blow-up/blow-down duct system. HVAC ducts should not be run in exterior walls or the slab. 

Air-Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as band joists 

and between attached garages and living spaces. These are discussed below because they have proven to 

be consistent challenges for high-performance production builders. 

Band joists. Continuity of an exterior air barrier can be maintained at the band joist with sealed or taped 

housewrap or rigid foam insulation. Continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, rigid draft-stopping (wood blocking) and sealant/caulk, 

or spray foam. Note that neither cellulose nor fiberglass (batt or blown) can be used for the air barrier. 

The air barrier detail on second-story band joists is important because it is inaccessible (covered by 

structural/finish floor and ceiling finish) after construction. The air barrier/thermal barrier detail is 

important on ground floor band joists because of the thermal bridge that can occur at the top of 

crawlspace foundation walls (as the result of the air barrier and thermal barrier moving from the outside 

to the inside of the building envelope and termite inspection zones located at the top of basement and 

crawlspace foundation walls). Note that while fiberglass batts fulfill the requirement for protection from 

ignition in the open band joists, fiberglass batt material by itself cannot maintain the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 4-9 and 

www.buildingscience.com/housesthatwork/airsealing/default.htm for details in terms of using sealants 

and rigid insulation to create a continuous air barrier between the attached garage and living space. 

Figure 4-9. Creating a continuous air barrier 
 

4-18

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resrouces/walls/insulation_sheatings.pdf). The wall assembly in the 

“Sacramento” permits drying to the interior and limited drying to the exterior (vapor semi-permeable XPS 

insulation on the second story, OSB on the first story). 

Drainage Plane, Air barrier, and Vapor Control 

The drainage plane in this wall assembly is the layer of building paper on both stories. 

The air barrier is the interior gypsum board installed using the Airtight Drywall approach (see Air Sealing 

Details). The wall and roof assemblies in this building are “flow-through” assemblies, with some degree 

of vapor permeability in all components of the wall and roof. This bi-directional drying is the preferred 

approach in Mixed-Dry climates. The most common exterior rigid insulation used in this assembly is 

expanded polystyrene (EPS), a semi-vapor permeable sheathing. 

Rough Opening Flashing 

Window and door flashing details are wall assembly or cladding specific and depend on whether the 

windows are installed before or after the drainage plane. Refer to the EEBA Water Management Guide for 

(www.eeba.org/bookstore) more information 

Advanced framing 

This wall assembly employs all of the advanced framing methods, including structural bracing rather than 

structural sheathing on the first floor. For advanced framing details, see

www.buildingscience.com/resources/misc/wood_efficiency.pdf. For information on the inset shear panel 

developed as part of a comprehensive approach to advanced framing in seismic regions, see Figure 4-10 

and www.buildingscience.com/resources/walls/default.htm. 
 

4-19

Fig. 66. Advanced framing detail 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed-cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains the same wall height). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult, if not impossible, to assess before 

completion of the structure—residual confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides), methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-Slab Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 

practical, and the only capillary break between the slab and ground is the polyethylene vapor barrier. 

Thermal Barrier 

In Sacramento, the heat loss through the slab perimeter is significant enough to warrant slab-edge 

insulation. 

Figure 66. Advanced shear wall framing 
 

4-20

Vented Attic 

Soffit and ridge vents provide more effective attic ventilation than gable-end vents. Gable exhaust fans do 

not provide effective attic ventilation. They are generally temperature-controlled, when relative humidity 

is often the condition that requires higher ventilation rates. They can also depressurize the house causing 

loss of conditioned air. Generally, the area of the gable and soffit vents, combined with the leakage of the 

attic ceiling, is such that the fan pulls air not just from the exterior vent, but also from the conditioned 

space below. 

Climate-Specific Details 

Mechanical Systems 

Heating. We recommend a sealed combustion hot-air furnace. Sealed combustion allows the unit to be 

located within the conditioned space with no compromise in indoor air quality or combustion safety. 

Cooling. Although evaporative cooling is prevalent in Mixed-Dry Climates, we recommend refrigerant 

cooling in high-performance homes in this climate region for three reasons: 

1. Refrigerant cooling permits year-round controlled ventilation; evaporative cooling does not. 

2. Evaporative cooling can be prone to moisture and indoor air quality problems without frequent 

and diligent system maintenance. Refrigerant cooling is not. 

3. While there can be a slight energy penalty with refrigerant cooling in comparison to evaporative, 

this penalty must be balanced against the year-round comfort provided by refrigerant cooling 

(evaporative cooling has difficulty supplying comfort in high humidity situations) and the 

substantial water savings associated with refrigerant cooling (a growing issue in mixed-dry 

climates). 

Follow appropriate sizing procedures. For more detailed information, see

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf.

Transfer Grilles. The single central return requires transfer grilles to provide an adequate return path 

and avoid pressurizing bedrooms, as shown in Figure 4-11. For appropriate sizing of ducts, including 

these pressure relief methods, go to 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf.

Controlled Mechanical Ventilation. We recommend an intermittent central-fan-integrated supply, 

designed to provide the ASHRAE 62.2P recommended flow rate, with fan cycling controls set to operate 

the central air handlers 20 minutes every hour to provide ventilation air distribution and whole-house 

averaging of air quality and comfort conditions (installed cost: $125 to $150). Include a normally closed 

motorized damper in the outside duct with the AirCyclerTM FRV control (installed cost: $50 to $60) (See 

Figure 4-12). 
 

4-21

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 

Landscaping for Wildfire Control 

Keeping woody materials of any type, living or otherwise, away from the building is good practice in dry 

climates where wildfires present a significant risk. 

Figure 4-11. Transfer grilles and jump ducts 
 

4-22

Figure 4-12. HVAC configuration in the “Sacramento” 

Field Experience Notes 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow highperformance start-up procedures such as those described on the BSC web site 

(www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf). In dry 

climates, it is generally a good idea to set up the air distribution fan to run a little longer at the end of each 

cycle to bump up the sensible efficiency. 
 

4-23

Energy Trusses 

There are a number of different truss configurations that yield greater depth at the heel, but they vary 

quite a bit in cost. The truss shown in Figure 4-13 (sometimes called a “slider” truss) has proven to be 

among the most cost-competitive. And of course, the pitch of the roof affects just how much insulation 

you can get at this location, regardless of the type of truss.

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Slab 

In dry climates, it is quite common for builders to use a sand layer in between the polyethylene sheet 

(“poly”) and the cast concrete to prevent differential drying and cracking problems. This moistureholding layer should never be placed between the poly and concrete. Differential drying and subsequent 

cracking should be handled with a low-water-content concrete and wetted burlap covering. For more 

information, see www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm.

Figure 4-13. Slider truss 
 

4-24

Single-Story Homes and Unvented/Conditioned Attic 

Keeping all ducts and HVAC equipment in conditioned space with slab-on-grade, single story homes can 

be accomplished by moving the thermal barrier and air barrier up to the roof line, making the attic an 

unvented, conditioned space (Figure 4-14). Below are the associated building science points to consider 

when making the change to an unvented roof/conditioned attic:

Air Sealing Details. Unvented assemblies (walls or roofs) are robust when the air sealing is robust. The 

hardest spots are not the fields but the margins/edges of assemblies. Spray foam applied at the margins 

(truss/rafter end blocking) may seem more expensive than cutting in air stops and caulking between each 

truss or rafter, but the labor savings and air sealing quality of spray foam make it a better choice. 

Cavity Insulation. Cellulose netting or fiberglass batt supports create the insulation “belly” and 

accommodate cavity fill depth that exceeds the depth of the truss top chord. 

Local Acceptance. This assembly may require discussion with the local building code official. See our 

Unvented Roof Summary Article for assistance at 

www.buildingscience.com/resources/roofs/unvented_roof_summary_article.pdf.

HVAC Configuration. See Figure 4-12 for the basic HVAC setup in this structure. 

Moving this Assembly to Mixed-Dry Climates. If an unvented roof/conditioned attic assembly is 

employed where the coldest monthly average temperature drops below 45°F, we recommend that a rigid 

insulation be added exterior to the structural roof deck to warm the assembly to the interior of the rigid 

insulation, thereby reducing the potential for condensation problems in the structural roof deck. See 

Figure 4-14 and “Insulations, Sheathings, and Vapor Diffusion Retarders” 

(www.buildingscience.com/resources) for more information: 

Tile roof. Tile roofs perform particularly well in this climate and are generally recommended when an 

unvented attic is used. See www.energystar.gov/ia/products/prod_lists/roof_prods_prod_list.xls for more 

information. 

Material Compatibility and Substitutions 

Interior Latex Paint 

The substitution of low-permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is important in mixed climates. 

Exterior Sheathing Materials 

In the second story of this assembly, the use of a reservoir cladding suggests that a moisture sensitive 

material such as fiberboard should not be used. On the other hand, the lack of cavity-warming exterior 

insulation means that an impermeable sheathing such as thin-profile structural sheathing (e.g., ThermoPly®, Energy Brace) should not be used. Plywood is an acceptable substitution for OSB in this wall 

assembly. For more information, see the Building Materials Property Table (Table 1) or the BSC paper 

“Insulations, Sheathings, and Vapor Diffusion Retarders” 

(www.buildingscience.com/resources/walls/insulation_sheathings.pdf)
 

4-25

Cavity Insulation Materials 

Acceptable cavity insulation includes any that have relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Flooring 

Because curing concrete releases significant moisture for several months after being cast, we recommend 

that a low w/c concrete ratio (<0.45) be used to protect the integrity of finished flooring. We also 

recommend that vinyl flooring not be installed over a concrete slab. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, and kitchens, are excellent candidates 

for non-paper faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 

HVAC 

A hot water-to-air coil in an air-handling unit can be used to replace the gas furnace heat exchanger. The 

coil can be connected to a standard gas water heater with a draft hood located in the garage, outside the 

conditioned space. Alternatively, the gas water heater can be sealed combustion (or power-vented) and 

located within the conditioned space. However, before you make this change, be sure to read the 

following technical resource: “Combo Space/Water Heating Systems – “Duo Diligence”

(www.buildingscience.com/resources/mechanical/combo_systems.pdf). 

Figure 4-14. Unvented, conditioned attic design 
 

4-26

Building Profile #13. The Tucson 

Foundation: Slab-on-grade Attic: None Cladding: Stucco 

Above Grade Wall: Wood frame Roof: Membrane

Figure 4-15. Cross section of the Tucson 
 

4-27

Building Science Details 

Ducts in Conditioned Space 

This building profile is designed to accommodate HVAC equipment and ducts in the living space, 

specifically in dropped soffits and in a utility space in the building core. HVAC ducts should not be run in 

exterior walls or the slab. 

Air Sealing Details at Transitions 

Air sealing can be particularly difficult, but no less important, at assembly transitions such as top-ofwall/roof assembly junctions and between attached garages and living spaces. These are discussed below 

because they have proven to be a consistent challenge for high performance production builders. 

Top-of-wall/roof assembly junction. The continuity of an exterior air barrier can be maintained at this 

junction if the air barrier material (foam insulation or stucco cladding, for example) is used continuously 

for the wall, soffit, and fascia. The continuity of an interior air barrier can be maintained through a 

combination of cut foam blocks and sealant/caulk, or spray foam. Note that neither cellulose nor 

fiberglass (batt or blown) can be used for the air barrier. 

Attached garages. The building envelope surfaces shared between conditioned space and an 

unconditioned garage must have a continuous air barrier. See Figure 4-16 and 

www.buildingscience.com/housesthatwork/airsealing/default.htm for details in terms of using sealants 

and rigid insulation to create a continuous air barrier between the attached garage and living space. 

Figure 4-16. Creating a continuous air barrier 
 

4-28

Drying Mechanisms 

In any climate, vapor control is based on the relationships among the following: the permeability of wall 

components, the type of cladding (reservoir or non-reservoir), the presence/lack/nature of an air space, 

and the magnitude/duration of the vapor drive (based on the relationship between the exterior and interior 

moisture content and temperature differences). The type of sheathing and housewrap used in any wall 

assembly must be based on an understanding of these inter-relationships. See “Insulations, Sheathings, 

and Vapor Diffusion Retarders” for more information 

(www.buildingscience.com/resources/walls/insulation_sheathing.pdf). This wall assembly permits drying 

to both the interior and the exterior (depending on the selection of exterior sheathing). For further details, 

see the Building Material Properties Table (Table 1). 

Drainage Plane, Air Barrier, and Vapor Control 

The drainage plane in this wall assembly is the Dupont StuccoWrap® weatherlapped onto the OSB 

structural sheathing (the paper-backed lath serves as the bond break for the stucco cladding). An annual 

precipitation of 8 in. (30-year average for Tucson) means that a face-sealed stucco cladding can work, but 

this system is designed with a drainage plane as a “belt and suspenders” approach for long-term 

durability. 

The air barrier is the interior gypsum board installed using the Airtight Drywall Approach (see Air 

Sealing Details). 

The wall assembly in this building is a “flow-through” assembly, with moderate to high relative vapor 

permeability in all components. This bi-directional drying is the preferred approach in mixed-dry 

climates. The membrane roof in this building means that drying to the interior is essential, and vapor 

permeable components and interior finishes should be used. 

Rough Opening flashing 

Window and door flashing details are wall assembly or cladding specific and depend on whether the 

windows are installed before or after the drainage plane. Refer to the EEBA Water Management Guide for 

more information (www.eeba.org/bookstore). 

Advanced Framing 

This wall assembly employs all of the advanced framing methods except alternative shear resistance 

(structural sheathing is used). For advanced framing details, see 

www.buildingscience.com/housesthatwork/details.htm. 

Framing on Slabs 

Installing a capillary break between the sill plate and a concrete slab on all walls—exterior, interior, 

partition—is good practice. A closed cell foam sill sealer or gasket works well. Alternatively, a strip of 

sheet polyethylene can be used. This isolates the framing from any source of moisture that may be either 

in or on the concrete slab (and using sill sealer on all walls maintains wall height exactly the same). 

Soil Gas Ventilation 

The sub-slab to roof vent system handles conditions that are difficult if not impossible to assess before 

completion of the structure, such as residual confined concentrations of air-borne radon, soil treatments 

(termiticides, pesticides) methane, etc. The cost of this “ounce” of prevention is well balanced against the 

cost of the “pound” of cure. 

Sub-Slab Stone Bed 

The 4-in.-deep, 3/4-in. stone bed functions as a granular capillary break, a drainage pad, and a sub-slab air 

pressure field extender for the soil gas ventilation system. Without it, a soil gas ventilation system is not 
 

4-29

practically possible, and the only capillary break between the slab and ground is the polyethylene vapor 

barrier. 

Thermal Barrier 

In all but the slab foundation, the thermal barrier is accomplished by cavity insulation. Slab insulation is 

not necessary in this climate, because the heat loss and gain is not sufficient to warrant insulation, from 

either an energy or building-science perspective. 

Roofing 

Light-colored membrane roofing performs better than conventional dark colored membrane roofing in 

this climate. See www.energystar.gov/ia/products/prod_lists/roof_prods_prod_list.xls for more 

information. 

Climate-Specific Details 

Mechanical Systems 

Heating. We recommend a sealed-combustion hot-air furnace. Sealed combustion allows the unit to be 

located within the conditioned space with no compromise in indoor air quality or combustion safety. See 

Figure 4-17 for the space conditioning system layout. 

Cooling. Although evaporative cooling is prevalent in Hot-Dry Climates, we recommend refrigerant 

cooling in high-performance homes in this climate region for three reasons: 

1. Refrigerant cooling permits year-round controlled ventilation. Evaporative cooling does not. 

2. Evaporative cooling can be prone to moisture and indoor air quality problems without frequent 

and diligent system maintenance. Refrigerant cooling is not. 

3. While there can be a slight energy penalty with refrigerant cooling in comparison to evaporative 

cooling, this penalty must be balanced against the year-round comfort provided by refrigerant 

cooling (evaporative cooling has difficulty supplying comfort in high humidity situations) and the 

substantial water savings associated with refrigerant cooling (a growing issue in Hot-Dry 

climates). 

Follow appropriate sizing procedures. For more details, see 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 
 

4-30

Figure 4-17. Heating and cooling system layout 

Ducting. The single central return requires transfer grilles to provide an adequate return air path and avoid 

pressurizing bedrooms, as shown in Figure 4-18. Appropriate sizing for ducts, including these pressure 

relief methods, can be found at 

www.buildingscience.com/resources/mechanical/509a3_cooling_system_sizing_pro.pdf. 

Figure 4-18. Transfer grilles and jump ducts 
 

4-31

Controlled mechanical ventilation. We recommend an intermittent central-fan-integrated supply, 

designed to provide the ASHRAE 62.2P recommended flow rate, with fan cycling controls set to operate 

the central air 20 minutes every hour to provide ventilation air distribution and whole-house averaging of 

air quality and comfort conditions (installed cost: $125 to $150). Include a normally closed motorized 

damper in the outside duct with the AirCyclerTM FRV control (installed cost: $50 to $60). For more 

information on controlled mechanical ventilation, see 

www.buildingscience.com/resources/mechanical/default.htm. 

Termite Management 

Termites are best managed with a three-pronged approach that deals with the three things termites need—

cover from sunlight, moisture, and food (wood or paper): 

Reduced cover. Keep plantings 3 ft away from the building perimeter, thin the ground cover (wood 

mulch or pea stone) to no more than 2 in. depth for the first 18 in. around the building, and maintain any 

termite inspection zone on the exterior of the foundation above grade. 

Control moisture. Maintain slope away from building as shown, carry roof load of water at least 3 ft 

away from building, and make sure that irrigation is directed away from the building. 

Chemical treatment. Use an environmentally appropriate soil treatment (such as Termidor®) and a 

building materials treatment (such as Bora-Care®) for termite-prone near-grade wood materials. 

Inter-relationship of first three points. Because a builder and a homeowner’s ability to employ or stick 

to each of the three strategies above will vary, make sure that an inability to fully employ one strategy is 

compensated for by complete rigor with the others. For example, if chemical treatment of soil or building 

materials is not an option, then complete rigor in moisture control and ground cover is required. 

Landscaping for Wildfire Control 

Keeping woody materials of any type, living or otherwise, away from the building is good practice in dry 

climates where wildfires present a significant risk. 

Field Experience Notes 

HVAC Commissioning 

The most efficient equipment means little if the system is not set up and started up properly. Follow highperformance start-up procedures such as those described on the BSC web site 

(www.buildingscience.com/resources/mechanical/air_conditioning_equipment_efficiency.pdf). In dry 

climates, it is generally a good idea to set up the air distribution fan to run a little longer at the end of each 

cycle to bump up the sensible efficiency. 
 

4-32

Location of HVAC Outdoor Unit 

It’s tempting to put the condenser right on the roof where the evaporative cooling unit was, particularly 

when lot lines are very tight. We do not recommend a rooftop location for the condenser for several 

reasons: It makes even routine maintenance more difficult, it puts the unit at what is most likely the 

hottest spot on the entire property, and it introduces more roof penetrations.

Advanced Framing 

For a technical resource that may help with resistance to advanced framing methods from local code 

officials, see the Building Safety Journal article written by Nathan Yost of BSC at 

www.buildingscience.com/resources/articles/16-19_Yost&Edminster_for_au.pdf.

Slabs 

In dry climates, it is quite common for builders to use a sand layer in between the polyethylene sheet 

(“poly”) and the cast concrete to prevent differential drying and cracking problems. This moistureholding layer should never be placed between the poly and concrete. Differential drying and subsequent 

cracking should be handled with a low-water-content concrete and wetted burlap covering. For more 

information, see www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm.

Moving this Assembly to Mixed-Dry Climates 

This “flat-roof” assembly is routinely moved to colder climates without any change in the 

design/construction of the assembly. We recommend that in any climate where the average monthly 

temperature for the coldest month drops below 45°F, one of the following four methods be employed to 

significantly reduce the potential for condensation problems in the structural roof deck (Figure 4-19): 

1. Add rigid insulation above the roof deck, raising the temperature of the roof deck to control 

condensation. Rigid polyisocyanurate insulation is recommended for its temperature stability. 

The amount of rigid insulation required is calculated based on the climate location. See 

“Insulations, Sheathings and Vapor Diffusion Retarders” 

(www.buildingscience.com/resources/walls/insulation_sheathing.pdf). 

2. Spray rigid foam insulation on the underside of the roof deck and cover with fibrous cavity 

insulation. The thickness of the spray foam insulation is calculated as in #1 above. 

3. Locate all of the insulation above the roof deck. 

4. Spray the entire cavity with foam insulation. 
 

4-33

Figure 4-19. Flat-roof assembly 

Material Compatibility and Substitutions 

Interior Latex Paint 

The substitution of low permeability interior finishes (vinyl wall paper, oil-based paints) for latex paint is 

strongly discouraged because drying to the interior is important in mixed climates. 

Building Papers with Stucco 

There must always be two separate components here: the bond break material and the drainage plane. 

Although StuccoWrap® is advertised as both a drainage plane material and the layer receiving the stucco, 

these two components should never be combined or reversed. 

Exterior Sheathing Materials 

In this assembly, the use of a reservoir cladding requires that a moisture-sensitive material such as 

fiberboard should not be used. Plywood is an acceptable substitution for OSB in this wall assembly. For 

more information, see the Building Materials Property Table (Table 1) or “Insulations, Sheathings, and 

Vapor Diffusion Retarders” (www.buildinscience.com/resources/walls/insulation_sheating.pdf). 

Cavity Insulation Materials 

Acceptable cavity insulation includes any that have relatively high vapor permeability—cellulose, 

fiberglass, or foam (as long as air sealing is accomplished by a separate component or system when 

cellulose or fiberglass is used). The decision may also be based on properties other than building science. 

Flooring 

Because curing concrete releases significant moisture for several months after being cast, we recommend 

that a low w/c concrete ratio (<0.45) be used to protect the integrity of finished flooring. We also 

recommend that vinyl flooring not be installed over a concrete slab. 

Gypsum Wallboard 

Areas of potentially high moisture, such as bathrooms, basements, and kitchens, are excellent candidates 

for non-paper-faced wallboard systems (e.g., James Hardie’s Hardibacker®, GP’s DensArmor®, USG’s 

Fiberock®). In addition, paper-faced gypsum board should never be used as interior sheathing or backer 

for tub or shower surrounds where ceramic tile or marble (any material with joints or grout lines) is used 

as the finish. 
 

A-1

Appendix A: Unvented Roof Summary Article 

“Unvented Attic Discussion,” Revised January 2003, Joseph Lstiburek. 

Unvented Roof (Conditioned Attics): Theory and Practice 

Building codes typically require attic ventilation; the origin of this requirement comes from cold climate 

demands to avoid ice damming and vent internally generated moisture. In hot (cooling-dominated) 

climates, the purpose of attic ventilation is to remove solar gain from the roof, thereby reducing the 

contribution of roof cooling load. In typical houses, the contribution of the roof-cooling load to the total 

load is on the order of 10%. 

However, our modeling and research has shown that the requirement for venting attics in hot-dry and hothumid climates is of questionable validity. Our studies on houses in various locations (including Las 

Vegas, Tucson, and the southeastern United States) have shown that by moving the ceiling air barrier and 

thermal barrier to the roof plane, better building airtightness can be achieved, and that the elimination of 

heat gain to the attic ductwork (as a result of conduction and leakage) more than offsets the additional 

heat gain caused by not venting the attic. 

Placement of the air handler and ductwork system in this conditioned attic space negates the effect of duct 

leakage, which is commonly 10%-20% of the rated air handler flow in typical construction. For houses 

with tile roofs, operating temperature for this “conditioned attic” or “attic utility area” has been measured 

at typically within 5° to 7°F of indoor temperatures, without any direct space conditioning (i.e., 

conditioned by duct leakage and conduction); this provides less harsh operating conditions for the 

ductwork and air handler than typical unconditioned attics. 

An excellent (and entertaining) discussion of the basics is found in the article: “Unvented Attic 

Discussion” (Lstiburek 1999). 

Detailed studies are also on the same web page; the paper that addresses both computer models and test 

houses is “Measurement of Attic Temperatures and Cooling Energy Use In Vented and Sealed Attics in 

Las Vegas, Nevada.” The paper “Questions posed regarding unvented roofs” provides a summary of 

typical questions on the performance and applicability of unvented roof systems. 

Unvented Roof Assembly Details (Air and Thermal Barriers) 

Moving the thermal and air barrier from the flat ceiling plane to the roof deck requires special detailing; 

because the attic is now conditioned space, it must be air sealed and insulated. Typical areas requiring 

draftstopping are the intersection between the “conditioned attic” and the “unconditioned attic” typically 

found over the garage or the porch. Details addressing these air barrier questions show the requirement 

for thermal barrier (i.e., insulation) and air barrier continuity around all of the conditioned space. 

In addition to this prescriptive detailing, the houses should be subjected to a blower-door test protocol, 

with the attic hatch open, which tests the airtightness of the entire building shell, including the unvented 

roof. This test truly determines whether the air barrier details, taken in aggregate, are effective. We 

recommend the airtightness goal used in the Building America program. The airtightness goal is based on 

the surface area of the building, and is tighter than the majority of typical residential construction. 

Of course, controlled mechanical ventilation is a recommended addition to all houses. 

Unvented Roof Assembly Material Performance 

One of the first questions brought up when unvented roof systems are proposed is whether it will be 

detrimental to the life of the building materials in the assembly. In addition to measuring the energy 
 

A-2

performance of test houses in various locations, Building Science Corporation also measured 

temperatures of attic air, roof sheathing (plywood/OSB), and roof tiles or shingles. 

The resulting data showed that when a vented tile roof in Las Vegas was compared with an unvented 

cathedralized roof, the maximum roof sheathing temperature difference was 17°F (see “Questions posed 

regarding unvented roofs”). The maximum measured roof sheathing temperature of 154°F for the 

unvented attic was well within acceptable temperature limits (less than 180°F) (see “Unventedcathedralized attics: Where we’ve been and where we’re going”). 

Furthermore, Las Vegas would be among the “worst case” locations for elevated temperatures of building 

materials (108°F ASHRAE 0.4% design temperature); few locations (e.g., Phoenix) have design 

conditions worse than that location. 

The air handler and HVAC system (ductwork) are operating at much less stressful temperatures (within 

3° to 5°F of indoor setpoint, instead of typical attic temperatures), and no ultraviolet light enters via roof 

vents. These factors will tend to increase lifespan of this mechanical equipment and ductwork systems in 

unvented roofs. 

Climate Data 

As mentioned in “Questions posed regarding unvented roofs,” unvented attics with cathedralized 

insulation can be recommended in the continental United States wherever the monthly average outdoor 

dry bulb temperature does not fall below 45°F; this coincides with the definition of a hot-dry or hothumid climate. 

This temperature limitation is a function of potential condensation problems within the roof assembly. 

The logic behind this decision is detailed in the web page “Unvented Roof Systems.” As mentioned in 

that article, unvented assemblies can be built in mixed or cold climates, but further detailing is necessary. 

At www.weather.com (The Weather Channel Web Site), monthly average temperature information is 

available, in order to determine climate location (cold, mixed, or hot zone). Data for Tucson, Arizona, are 

shown below; it shows a lowest monthly temperature averaging above 45°F: 

Tucson, AZ Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Mean outdoor temp (°F) 66 74 84 87 85 81 71 59 52 52 55 59 66 
 

A-3

Tucson, Arizona, Average Monthly Temperatures

0

10

20

30

40

50

60

70

80

90

100

April

May

June

July

August

September

October

November

December

January

February

March

April

Temperature (F)

Mean monthly outdoor temperature

Condensing Temperature

In addition, this data includes average precipitation records, which will allow the differentiation between 

humid and dry climate zones (i.e., over 20 in./year or under). Tucson’s historical data shows an average 

precipitation per year of ~13 in. (hot dry zone). 
 

A-4

References for this Article 

Kohta Ueno, Building Science Corporation, 2003 

This article was written to tie together and summarize the various papers on unvented conditioned 

cathedralized attics found on our website. We realize that there is a wealth of information, and 

much of it too detailed to understand or digest in a single sitting. Furthermore, building officials 

might not have the time available to carefully examine the many documents on the page; this is 

meant to summarize the main arguments, and provide pointers to where detailed information and 

measured data can be found. 

The articles dealing with unvented roofs are as follows (in chronological order): 

From www.buildingscience.com/resources/resources.htm#Roofs 

“Measurement of Attic Temperatures and Cooling Energy Use In Vented and Sealed Attics in Las Vegas, 

Nevada.” Armin F. Rudd, Joseph W. Lstiburek, and Neil A. Moyer. Presented at the ‘96 

Excellence in Building Conference, 14-17 November, and published in EEBA Excellence, The 

Journal of the Energy Efficient Building Association, Spring 1997. Energy Efficient Building 

Association, Minneapolis, MN 

“Vented and Sealed Attics In Hot Climates.” A. F. Rudd and Joseph W. Lstiburek. Presented at the 

ASHRAE Symposium on Attics and Cathedral Ceilings, Toronto, June 1997. ASHRAE 

Transactions TO-98-20-3. American Society of Heating Refrigeration and Air-Conditioning 

Engineers, Atlanta, GA. 

BSC Figures 1 and 2 (Unvented Roof Insulation and Framing Details, Air Barrier at Unvented Roof) 

 “Questions posed regarding unvented roofs.” A. F. Rudd. 2000. 

“Unvented-cathedralized attics: Where we’ve been and where we’re going.” A. F. Rudd, Joseph W. 

Lstiburek, and Kohta Ueno. 2000. 

“Unvented Roof Systems. ” Joseph W. Lstiburek. 2001. 

“Unvented Roofs, Hot-Humid Climates, and Asphalt Shingles.” January 2003, Joseph Lstiburek.
 

B-1

Appendix B: Sand Layers Should Not Be Placed Between 

Polyethylene Vapor Barriers and Concrete Floor Slabs 

by Joseph Lstiburek, Ph.D., P. Eng. 

Excess slab moisture intrusion problems resulting in flooring failures, mold growth, and other microbial 

contamination problems are typically caused by sand layers located between polyethylene vapor barriers 

and concrete floor slabs. 

The sand layers become reservoirs for water in the liquid state (bulk water) that enters the sand layers by 

gravity flow from the top, sides and bottom of the sand layers (Figure 1). The liquid water is both held in 

the sand layers and redistributed within the sand layers by capillarity (Figure 2). Additionally, because of 

these capillary forces, the liquid water is incapable of draining out of the sand layers. The only 

mechanism of drying of the sand layers is upwards through the concrete slabs by vapor diffusion and 

capillary draw (Figure 3). 

There is no barrier or protection for the upward moisture flow through the concrete slabs from the wetted 

sand layers. The intended protection for upward moisture flow from below grade are the polyethylene 

vapor barriers, but this intended moisture protection has been rendered ineffective by the gravity flow 

wetting mechanism that has saturated the sand layers that are located above the polyethylene vapor 

barriers. 

 
 

B-2

The moisture flow upwards through the concrete slabs by vapor diffusion and capillary transmission 

passes through the top surface of the concrete slabs, as well as through floor surface treatments and leads 

to mold and other microbial contamination problems. 

The rate of wetting of the sand layers by the gravity-flow wetting mechanism is several orders of 

magnitude larger then the rate of drying of the sand layers by the vapor diffusion and capillary 

transmission drying mechanism. The sand layers become water reservoirs that continually supply water 

for the upward flow through the concrete slabs by vapor diffusion and capillary transmission. 

Picture the sand layers as "blotter paper" that, once wetted, do not let water drain out of them. The only 

method of drying available to the "blotter paper" is evaporation. In the case of the sand layers the only 

method of "evaporation" is upward through the concrete slabs because of the presence of the polyethylene 

vapor barrier under the sand layers. 

Concrete slabs should be placed in direct contact with polyethylene vapor barriers. A sand layer should 

not be installed between concrete slabs and polyethylene vapor barriers. 

Where concrete slabs are in direct contact with polyethylene vapor barriers a reservoir is not created if 

rainfall occurs during the construction process and penetrates the slab or if wet curing is used. 

Additionally, wet concrete cutting operations, cracks in slabs, gaps and penetrations in the polyethylene 

vapor barrier coupled with cleaning, water testing, ground water migration or irrigation do not affect slab 

moisture transmission if a reservoir is absent or cannot be created between the polyethylene and the 

concrete slab. 

When concrete slabs are cast directly over polyethylene vapor barriers, the concrete water-to-cement 

(w/c) ratio must be correctly specified in order to control bleed water and plastic shrinkage cracking. 

Bleed water will not be present if the w/c ratio is below 0.5, and plastic shrinkage cracking becomes 

negligible when the w/c ratio is below the range of 0.48 to 0.45. Differential drying and slab curl are 

controlled with either a curing compound or a temporary covering of plastic sheeting. 

Concrete slabs with a w/c ratio of 0.45 or less should be placed directly on a polyethylene vapor barrier 

coupled with a curing compound or a temporary plastic sheeting slab covering in order to avoid problems. 

The following four reasons are generally cited for using a sand layer over polyethylene vapor barriers: 

1. The sand layer controls bleed water with high w/c ratio concrete slabs 

2. The sand layer reduces curl with high w/c ratio concrete slabs when top-side curing is not 

controlled 

3. The sand layer reduces plastic shrinkage cracking with high w/c ratio concrete slabs 

4. The sand layer protects the polyethylene vapor barrier from punctures. 

The first three reasons are based on sound technical arguments. However, each of the first three are based 

on the condition that the sand layer be prevented from getting wet during the construction process and 

beyond and are typically associated with floor slabs that are placed "after the building is enclosed and the 

roof is watertight." Additionally, the first three are based on the condition that wet curing such as ponding 

or continuous sprinkling will not occur or that joint sawing using wet methods or power washing will not 

occur. The first three are also conditional on slab and foundation designs that will not be sensitive to 

ground water wetting from local water tables and local irrigation. 

In the case of exposed slab construction, the first three reasons are rendered moot because the conditions 

for their use are not met, nor can they be met. Accordingly, a sand layer should not be specified. 

The fourth reason, "puncture protection," is based on incorrect physics. A sand layer is not necessary to 

protect polyethylene vapor barriers. Vapor diffusion is a direct function of surface area. Rips, holes, tears, 

and punctures in sheet polyethylene vapor barriers constitute a very small surface area of vapor 
 

B-3

transmission compared to the total floor slab area. If 95% of the surface area of the slab is protected by a 

vapor barrier, then that vapor barrier is 95% effective. This holds true only if air flow or air leakage is not 

occurring through the vapor barrier. Where concrete is in direct contact with the polyethylene vapor 

barrier this is the case. Air flow is not occurring. The concrete slab is an "air-barrier" and the polyethylene 

is the "vapor barrier" and an effective vapor barrier even if the polyethylene has numerous punctures. 

In the case of exposed slab construction there is no justification for the use of a sand layer between the 

polyethylene vapor barrier and the concrete slabs. 

The specification of a sand layer over a polyethylene vapor barrier is typically directly responsible for 

flooring failures, cold, and microbial contamination problems. 
 

C-1

Appendix C. Summary of Building Profiles

Climate/ 

Building 

Profile 

# 

Stories 

Wall 

Type Foundation Wall Cladding Roof Roof Cladding 

Cold

Chicago 2 Stickframed 

Full basement/ 

cast concrete Vinyl siding Vented unconditioned attic Asphalt shingle 

Denver 2 Stickframed 

Full basement 

w/ sub-crawl 

Brick 

veneer/wood 

siding 

Vented 

unconditioned attic Asphalt shingle 

Minneapolis 1.5 Stickframed Slab-on-grade Stucco Vented cathedral Asphalt shingle 

Mixed-Humid

Atlanta 2 Stickframed Slab-on-grade Vinyl siding Vented 

unconditioned attic Asphalt shingle 

Charlotte 2 Stickframed 

Conditioned 

crawl/ block 

wall 

Brick veneer Vented 

unconditioned attic Asphalt shingle 

Louisville 1 Stickframed 

Full basement/ 

cast concrete Vinyl siding Vented cathedral Asphalt shingle 

Hot-Dry/Mixed-Dry

Albuquerque 1 Stickframed Slab-on-grade Stucco Vented 

unconditioned attic Asphalt shingle 

Sacramento 2 Stickframed 

Post-tensioned 

slab-on-grade Fibercement 

siding 

Vented 

unconditioned attic Tile 

Tucson 1 Stickframed Slab-on-grade Stucco None Low-slope 

membrane 

Hot-Humid

Houston 2 Stickframed Slab-on-grade Brick/ 

Fibercement Conditioned attic Asphalt shingle 

Orlando 2 

Block/ 

stick 

frame 

Block stem wall 

& slab Stucco Conditioned attic Tile 

Montgomery 1 Stickframed 

Conditioned 

crawl/ cast 

concrete wall 

Vinyl or 

aluminum lap 

siding 

Vented 

unconditioned attic 

Standing seam 

metal 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

March 2005 

2. REPORT TYPE

Subcontractor Report 

3. DATES COVERED (From - To)

January 2003 – December 2003 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Introduction to Buildings Systems Performance: Houses That Work 

II. Revised February 2005 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-550-37664 

5e. TASK NUMBER

BET5.8004 

6. AUTHOR(S)

Building Science Consortium 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Building Science Consortium 

70 Main St. 

Westford, MA 01886 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

KAAX-3-32443-01 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

NREL/SR-550-37664 

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

NREL Technical Monitor: Bob Hendron 

14. ABSTRACT (Maximum 200 Words)

Buildings should be suited to their environments. Design and construction must be responsive to varying seismic 

risks, wind loads, and snow loads, as well as soil conditions, frost depth, orientation, and solar radiation. In addition, 

building envelopes and mechanical systems should be designed for a specific hygro-thermal regions, rain exposure, 

and interior climate. The Building Science Consortium (BSC) design recommendations are based on the hygrothermal regions with reference to the annual rainfall. Local climate must be addressed if it differs significantly from the 

climate described for a particular design. 

15. SUBJECT TERMS

Building America; energy-efficient houses; Building Science Consortium; BSC; U.S. Department of Energy; DOE 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18
Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable

A Strong Energy Portfolio 

for a Strong America

Energy effi ciency and clean, renewable 

energy will mean a stronger economy, 

a cleaner environment, and greater 

energy independence for America. 

Working with a wide array of state, 

community, industry, and university 

partners, the U.S. Department of 

Energy’s Offi ce of Energy Effi ciency 

and Renewable Energy invests in a 

diverse portfolio of energy technologies.

Research and Development 

of Buildings

Our nation’s buildings consume more 

energy than any other sector of the 

U.S. economy, including transportation 

and industry. Fortunately, the opportunities to reduce building energy use—

and the associated environmental 

impacts—are signifi cant.

DOE’s Building Technologies Program 

works to improve the energy effi ciency 

of our nation’s buildings through innovative new technologies and better 

building practices. The program

focuses on two key areas:

• Emerging Technologies 

Research and development of the 

next generation of energy-effi cient 

components, materials, and 

 equipment

• Technology Integration

Integration of new technologies 

with innovative building methods 

to optimize building performance 

and savings

For more information contact:

EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov

An electronic copy of this factsheet is 

available on the Building America Web 

site at www.buildingamerica.gov

U.S. Department of Energy

Energy Effi ciency

and Renewable Energy

Building America Program

George S. James • New Construction • 202-586-9472 • fax: 202-586-8134 • e-mail: George.James@ee.doe.gov

Terry Logee • Existing Homes • 202-586-1689 • fax: 202-586-4617 • e-mail: terry.logee@ee.doe.gov

Lew Pratsch • Integrated Onsite Power • 202-586-1512 • fax: 202-586-8185 • e-mail: Lew.Pratsch@hq.doe.gov

Building America Program • Offi ce of Building Technologies, EE-2J • U.S. Department of Energy • 1000 Independence Avenue, S.W. • 

Washington, D.C. 20585-0121 • www.buildingamerica.gov

Building Industry Research Alliance (BIRA)

Robert Hammon • ConSol • 7407 Tam O’Shanter Drive #200 • Stockton, CA 95210-3370 • 209-473-5000 • fax: 209-474-0817 • 

e-mail: Rob@consol.ws • www.bira.ws

Building Science Consortium (BSC)

Betsy Pettit • Building Science Consortium (BSC) • 70 Main Street • Westford, MA 01886 • 978-589-5100 • fax: 978-589-5103 • 

e-mail: Betsy@buildingscience.com • www.buildingscience.com

Consortium for Advanced Residential Buildings (CARB)

Steven Winter • Steven Winter Associates, Inc. • 50 Washington Street • Norwalk, CT 06854 • 203-857-0200 • fax: 203-852-0741 • 

e-mail: swinter@swinter.com • www.carb-swa.com

Davis Energy Group

David Springer • Davis Energy Group • 123 C Street • Davis, CA 95616 • 530-753-1100 • fax: 530-753-4125 •

e-mail: springer@davisenergy.com • deg@davisenergy.com • www.davisenergy.com/index.html

IBACOS Consortium

Brad Oberg • IBACOS Consortium • 2214 Liberty Avenue • Pittsburgh, PA 15222 • 412-765-3664 • fax: 412-765-3738 •

e-mail: boberg@ibacos.com • www.ibacos.com

Industrialized Housing Partnership (IHP)

Subrato Chandra • Florida Solar Energy Center • 1679 Clearlake Road • Cocoa, FL 32922 • 321-638-1412 • fax: 321-638-1439 • 

e-mail: subrato@fsec.ucf.edu • www.baihp.org

National Association of Home Builders (NAHB) Research Center

Tom Kenney • National Association of Home Builders (NAHB) Research Center • 400 Prince George’s Boulevard • 

Upper Marlboro, MD 20774 • 301-430-6246 • fax: 301-430-6180 • toll-free: 800-638-8556 • www.nahbrc.org/ 

National Renewable Energy Laboratory

Ren Anderson • 1617 Cole Boulevard, MS-2722 • Golden, CO 80401 • 303-384-7433 • fax: 303-384-7540 • 

e-mail: ren_anderson@nrel.gov • www.nrel.gov

Tim Merrigan • 1617 Cole Boulevard, MS-2722 • Golden, CO 80401 • 303-384-7349 • fax: 303-384-7540 • 

e-mail: tim_merrigan@nrel.gov • www.nrel.gov

Oak Ridge National Laboratory

Pat M. Love • P.O. Box 2008 • One Bethel Valley Road • Oak Ridge, TN 37831 • 865-574-4346 • fax: 865-574-9331 • 

e-mail: lovepm@ornl.gov • www.ornl.gov

Produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory, a DOE national laboratory.

March 2005 • NREL/SR-550-37664

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste.

Visit our Web sites at:

www.buildingamerica.gov www.energystar.gov