Construction Guidelines for 

High R-Value Walls without 

Exterior Rigid Insulation

Lois B. Arena 

Consortium for Advanced Residential Buildings

July 2016
NOTICE

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iii

Construction Guidelines for High R-Value Walls without Exterior 

Rigid Insulation

Prepared for:

The National Renewable Energy Laboratory

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

Prepared by:

Lois B. Arena, PE 

Steven Winter Associates, Inc.

Consortium for Advanced Residential Buildings 

61 Washington Street 

Norwalk, CT 06854 

NREL Technical Monitor: Stacey Rothgeb 

Prepared under Subcontract No. KNDJ-0-40342-05

July 2016 
iv

The work presented in this report does not represent 

performance of any product relative to regulated 

minimum efficiency requirements.

The laboratory and/or field sites used for this work are 

not certified rating test facilities. The conditions and 

methods under which products were characterized for 

this work differ from standard rating conditions, as 

described.

Because the methods and conditions differ, the reported 

results are not comparable to rated product performance 

and should only be used to estimate performance under 

the measured conditions.
v 

Contents

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

Definitions................................................................................................................................................. viii

Abstract........................................................................................................................................................ 1

Acknowledgements .................................................................................................................................... 1

Progression Summary................................................................................................................................ 2

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

2 Decision-Making Criteria ..................................................................................................................... 5

2.1 Cost and Performance ................................................................................................................... 5

2.1.1 Framing ............................................................................................................................... 5

2.1.2 Insulation............................................................................................................................. 6

2.2 Insulation Continuity ....................................................................................................................... 7

2.2.1 Roof/Wall Connection ......................................................................................................... 7

2.2.2 Slab/Wall Intersections ....................................................................................................... 8

2.3 Durability and Moisture Issues ....................................................................................................... 9

2.4 Minimizing Disturbances of Insulation.......................................................................................... 10

3 Technical Description ........................................................................................................................ 12

3.1 Applicable Wall Systems .............................................................................................................. 12

3.2 Double-Wall Framing.................................................................................................................... 12

3.3 Electrical and Plumbing................................................................................................................ 14

3.4 Air Barriers.................................................................................................................................... 14

3.4.1 Interior Air Barriers ............................................................................................................ 14

3.4.2 Exterior Air Barriers........................................................................................................... 15

3.5 Insulation ...................................................................................................................................... 15

3.5.1 Single Insulation Strategy ................................................................................................. 15

3.5.2 Hybrid Insulation Strategy................................................................................................. 17

3.6 Moisture-Management System .................................................................................................... 18

3.6.1 Capillary Breaks ................................................................................................................ 19

3.6.2 Water-Resistive Barriers ................................................................................................... 19

3.6.3 Cladding ............................................................................................................................ 20

3.6.4 Mechanical Ventilation ...................................................................................................... 21

4 Measure Implementation ................................................................................................................... 22

4.1 Climate-Specific Factors .............................................................................................................. 22

4.2 Field Inspection ............................................................................................................................ 22

4.3 Install Procedure........................................................................................................................... 22

4.4 Foundation Details........................................................................................................................ 23

4.5 Wall Framing ................................................................................................................................ 25

4.6 Roof Connection........................................................................................................................... 26

4.7 Rim/Band Joist Details ................................................................................................................. 27

4.8 Windows and Doors ..................................................................................................................... 27

4.9 Weather-Resistive Barrier ............................................................................................................ 32

4.10 Insulation ...................................................................................................................................... 36

4.11 Drywall.......................................................................................................................................... 37

4.12 Cladding Attachment .................................................................................................................... 38

5 Verification Procedures and Tests ................................................................................................... 41

5.1 Air-Leakage Testing ..................................................................................................................... 41

5.2 Ventilation System Balancing and Commissioning...................................................................... 42

References................................................................................................................................................. 43

Appendix A: Compliance with U.S. Department of Energy Zero Energy Ready Home Criteria ........ 44
vi

List of Figures

Figure 1. Double-wall construction ........................................................................................................... 3

Figure 2. ocSPF in a 12-in. double wall..................................................................................................... 6

Figure 3. ccSPF in the outer stud cavity of a 12-in. double wall. Cellulose will fill the remainder of 

the cavity. .............................................................................................................................................. 6

Figure 4. Full-depth cellulose insulation in a 12-in. double wall............................................................ 6

Figure 5. Roof/wall intersection showing good continuity of insulation .............................................. 7

Figure 6. A shallow roof pitch resulting in the inability to install full-depth ceiling insulation over 

the entire depth of the wall cavity....................................................................................................... 7

Figure 7. ccSPF installed over the outer edge of the double wall to the desired R-value for the 

ceiling .................................................................................................................................................... 8

Figure 8. Flashing over slab edge insulation was taped to the sheathing using the manufacturer’s 

approved tape. The vented cladding was then attached with 3⁄4-in. furring strips, and it 

overlapped the flashing. ...................................................................................................................... 9

Figure 9. Insulation netting surrounds vents and plumbing penetrations in an exterior double 

wall. ...................................................................................................................................................... 11

Figure 10. Two-stud corners can be used for both the interior and exterior walls in the double-wall 

assembly. ............................................................................................................................................ 12

Figure 11. Reduced framing around windows on the interior wall...................................................... 12

Figure 12. Reductions in framing around the openings allows for more insulation in headers. ..... 13

Figure 13. Windows in double walls: (left) a framed window opening and (right) a set window ..... 14

Figure 14. Interior air barrier with all seams taped................................................................................ 14

Figure 15. Exterior air barrier with all seams taped .............................................................................. 14

Figure 16. Double wall before and after insulation with dense-blown cellulose................................ 16

Figure 17. Incomplete capillary break. It should be installed the entire depth of the wall to keep 

lumber and insulation from wicking up moisture. .......................................................................... 19

Figure 18. Example of a building wrap being used for the WRB ......................................................... 20

Figure 19. Image of liquid-applied WRB ................................................................................................. 20

Figure 20. Vertical furring strips create a vent space for horizontal fiber cement siding................. 21

Figure 21. Horizontal furring was used to attach a corrugated metal panel siding that allows 

vertical draining and venting of the sheathing................................................................................ 21

Figure 22. Typical blower door equipment used to detect air leakage through the building 

envelope .............................................................................................................................................. 41
vii 

List of Tables

Table 1. Additional Lumber Costs for Double Walls per 100 Linear Feet ............................................. 5

Table 2. 2012 IRC Requirements for Walls with a Class III Vapor Retarder........................................ 10

Table 3. Thermal Effects of Framing Factors on Double Walls............................................................ 13

Table 4. R-Values for Double Walls of Varying Thicknesses ............................................................... 17
viii

Definitions

ccSPF Closed-cell spray polyurethane foam

IRC International Residential Code 

ocSPF Open-cell spray polyurethane foam

WRF Water-resistive barrier
1 

Abstract

High R-value wall assemblies (R-40 and above) are gaining popularity in the market due to 

programs such as the U.S. Department of Energy Zero Energy Ready Home program, Passive 

House, Net Zero Energy Home challenges in several states, and highly incentivized retrofit 

programs. In response to this demand, several builders have successfully used double-wall 

systems to achieve higher R-values in thicker, framed walls. To builders of conventional stickframed homes, often one of the most appealing features of double-wall systems is that there are 

very few new exterior details. Exterior sheathings, structural bracings, house wraps or building 

paper, window and door flashings, and siding attachments are usually identical to good details in 

conventional framed-wall systems.

However, although the details in double-wall systems are very similar to those in conventional 

stick framing, there is sometimes less room for error. Several studies have confirmed colder 

temperatures of exterior sheathing in high R-value wall assemblies that do not have exterior rigid 

foam insulation. These colder temperatures can lead to increased chances for condensation from 

air exfiltration, and they have the potential to result in moisture-related problems (Straube and 

Smegal 2009, Arena 2014, Ueno 2015). 

The information presented in this guide is intended to reduce the risk of failure in these types of 

assemblies, increase durability, and reduce material brought to landfills due to failures and 

resulting decay. Although this document focuses on double-wall framing techniques, the 

majority of the information about how to properly construct and finish high R-value assemblies 

is applicable to all wall assemblies that do not have foam insulation installed on the exterior of 

the structural sheathing. The techniques presented have been shown through field studies to 

reduce the likelihood of mold growth and moisture-related damage and are intended for builders, 

framing contractors, architects, and consultants involved in designing and building superinsulated homes. The information is applicable to both new construction and gut-rehabilitation

projects in Climate Zones 5 and higher. 

Author

This is the first edition of this guide. It was authored by Lois B. Arena, PE, of Steven Winter 

Associates, Inc., lead for the U.S. Department of Energy Building America team Consortium for 

Advanced Residential Buildings. 

Acknowledgements

Steven Winter Associates acknowledges the U.S. Department of Energy Building America 

program and their funding and support for the development of this technical report as well as the

research that informed it. Steven Winter Associates would like to thank William Anderson from 

Metric Corporation and Michael Carpenter and the project manager Kendall Carpenter from 

AquaZephyr, LLC, for their continued cooperation and dedication throughout the studies that 

informed this guideline. Special thanks also to the residents of the Third Residential Ecovillage 

Experience (TREE) neighborhood at EcoVillage in Ithaca, New York, for their continued 

support, cooperation, and the use of their homes. 
2 

TEST AIR LEAKAGE 

Step Seven Verify that the building shell is airtight prior to 

installing drywall. This step is crucial to ensure that warm, moist 7 air does not enter the wall assembly.

Progression Summary

ss

1 

HIGH R-VALUE 

WALL 

CONSTRUCTION

Double-Wall Assemblies Although this guide focuses on the construction of double-wall 

assemblies, aside from the actual framing techniques (steps shown in orange below), the 

guidance provided is applicable to all high R-value walls without exterior rigid insulation in 

Climate Zones 5 and up.

FRAME AND 

SHEATH OUTER 

WALL

Step One The outer structural 2 x 4 wall is constructed using 

conventional framing techniques. Even though the overall 

efficiency will surpass code levels, advanced framing techniques 

that reduce lumber and thermal bridging are still recommended.

1

FRAME INNER 

WALL

Step Three The inner wall is constructed several inches in from 

the exterior wall so that the resulting cavity depth can 

accommodate the insulation thickness needed to achieve the 

specified R-value. This step can be interchanged with Step Two.

3

BOX OUT 

PENETRATIONS

Step Four To minimize disruption to the insulation if repairs are 

needed in the future, plumbing and electrical penetrations should 4 be boxed out before the insulation is installed.

AIR SEAL

Step Five The durability of high R-value walls is very dependent 

on minimizing air leakage into the cavity. Strict attention to air 

sealing is required. A blower door test to verify tightness is highly 

recommended at this time.

5

INSULATE

Step Six After steps 1 through 5 are completed, the insulation can 

be installed. Various types of insulation and combinations can be 

used. Hygrothermal analysis is highly recommended when 

combining types.

6

INSTALL WINDOWS 

AND DOORS

Step Two Install windows and doors. Follow best practices for 

properly incorporating these into the water management layer. 2 This step can be interchanged with Step Three.
3 

1 Introduction

During the last several years, the focus on energy efficiency has increased, and so have the 

requirements of energy-efficiency codes and performance programs. In fact, upon adoption of 

the 2012 International Energy Conservation Code, homes built in Climate Zone 6 and higher are

required to either install insulating sheathing on the exterior of the walls or increase the depth of 

the wall cavity to accommodate the increased insulation requirements. Additionally, due to 

programs such as Passive House, Net Zero Energy Home challenges in several states, and highly 

incentivized, deep, energy-retrofit programs, high R-value wall assemblies and assemblies that

employ a combination of insulation products are gaining popularity in the market. 

Several builders have successfully used double-wall systems to achieve higher R-values in 

thicker, framed walls (Figure 1). In this context, a double wall consists of a load-bearing external 

frame wall usually constructed with 2 x 4 framing at 16 in. on center. This wall is built and 

sheathed as a typical exterior-frame wall. After the building is enclosed, an additional frame wall 

is constructed several inches inside the external load-bearing wall to provide the depth required 

to achieve the desired R-value. 

Figure 1. Double-wall construction 

To builders of conventional stick-framed homes, often one of the most appealing features of 

double-wall systems is that there are very few new exterior details. Exterior sheathings, 

structural bracings, house wraps or building paper, and window and door flashings are usually 

identical to good details in conventional framed-wall systems. When transitioning from typical 

stick-frame construction to double walls, little to no additional training is needed, which allows 
4 

framers and builders to save money and compete with others that are building different, more 

expensive, high R-value assemblies.

However, although the details in double-wall systems are very similar to those in conventional 

stick framing, there is sometimes less room for error. For example, several studies have 

confirmed colder temperatures of exterior sheathing, which can lead to increased chances for 

condensation from air exfiltration (Straube and Smegal 2009, Arena 2014, Ueno 2015).

Depending on the temperature of the surfaces and the permeability of the materials, that moisture 

may get trapped inside of the walls, and it could potentially lead to mold growth and/or decay of 

the building materials. With the increased use of foam insulation, various vapor barrier 

applications, the drastic increase in retrofit activities, and the increasing thickness of the walls 

(all factors that can reduce the drying potential of the walls), moisture issues could become much 

bigger problems. 

These guidelines have been created to help reduce the risk of moisture-related damage with a 

particular focus on assemblies that have no exterior rigid insulation installed over the exterior 

structural sheathing such as double walls, Larsen truss assemblies, and structural insulated 

panels. The recommendations are based on research conducted to date and current best practices. 

Recommendations are provided for appropriate cladding options, ratios of impermeable to 

permeable insulation, and vapor retarder levels and placement. 
5 

2 Decision-Making Criteria

To increase the thermal performance of typical frame construction, one rather intuitive solution 

is to simply increase the thickness of the framing and thereby the insulation cavity. Although this 

is certainly an option, dimensional lumber for wall framing can be very expensive and difficult to 

work with. Engineered wall framing—such as I joists—are also an option, but these can be 

equally expensive and cumbersome.

Double walls offer a cost-competitive method of constructing high R-value walls, and they have 

already reached the commercialization stage. During the last five years, Steven Winter 

Associates, Inc., has consulted on several community-scale projects in the northeastern United 

States where double walls were the chosen construction method. That said, the following 

sections explore various cost and construction implications of using this framing method. 

2.1 Cost and Performance

2.1.1 Framing 

The additional labor to construct the second wall is one of the biggest costs related to doublewall construction. The additional framing requires approximately 4-5 person-days (32-40 personhours) for each 100 linear feet of double wall (Aldrich et. al. 2010). This is rather independent of 

wall height, but many corners, dormers, windows, and/or doors can substantially increase this 

value. Labor costs vary tremendously, but using an example framer’s rate of $35 per hour, the 

additional labor cost is $1,120 - $1,400 for each 100 linear feet of wall. 

The amount of exterior framing lumber needed is doubled, but this is usually somewhat offset by 

the exterior wall being constructed of 2 x 4 framing rather than 2 x 6 (required to meet code in 

most cold climates), which is often significantly more expensive than 2 x 4 framing. 

Consequently, increased lumber costs for double walls are much less than increased labor costs. 

A survey of lumber suppliers in the Northeast showed that 2 x 6 framing is currently 50% more 

costly than 2 x 4 framing of the same quality and length. Example costs are shown in Table 1. 

Table 1. Additional Lumber Costs for Double Walls per 100 Linear Feet

Length of 

8-ft. Wall

Framing 

Factor

Framing 

Needed

Framing Cost 

per Foot

Framing 

Cost

Single 2 x 6 Wall 100 ft. 20% 1,280 ft. $0.61 $781

Double 2 x 4 

Wall

100 ft. 20% 2,560 ft. $0.40 $1,024

Net Increase for Double Wall $243

Many of the framing-related costs—especially labor—can be managed by good building design 

and careful planning. Once familiar with the systems, there is not a substantial amount of 

additional time needed to design homes with double walls. It is important to note that these 

homes are usually very square and are designed for double walls. A conventional framed home 

with more corners and non-right angles requires substantially more framing time and material, so 

designers should be very conscious of the benefit of simple building footprints. 
6 

2.1.2 Insulation

Insulation is the second largest cost of a double-wall system. The main cost element is the extra 

insulation itself; the extra time needed to install the insulation is secondary. From working with 

builders of 12-in. double walls with blown cellulose insulation, insulation costs increase 30%-

40% more than the cost of insulating a comparable 2 x 6 framed wall (Tauer 2009, Perkins 

2009). 

In the author’s experience, dense-packed blown cellulose is the most common insulation used in 

these assemblies. Blown fiberglass is certainly an option, and open-cell spray polyurethane foam 

(ocSPF) can also be used to full depth. If using a combination of products, proper attention must 

be paid to the ratio of air-impermeable insulation (closed-cell spray polyurethane foam (ccSPF) 

to air-permeable insulation (fiberglass, cellulose) or condensation problems could occur. Figure 

2 through Figure 4 show photographs of three different insulation strategies for a 12-in.-deep 

double wall.

Figure 2. ocSPF in a 12-in. double wall Figure 3. ccSPF in the outer stud cavity of a 12-

in. double wall. Cellulose will fill the remainder of 

the cavity.

Figure 4. Full-depth cellulose insulation in a 12-in. double wall
7 

One noteworthy feature of the costs discussed above is that the additional framing labor is by far 

the largest component of the incremental costs, and this item is independent of wall thickness. 

Insulation cost, however, increases with wall thickness, and this is not a linear relationship

because the labor costs to prepare for and install dense-packed cellulose do not change 

significantly as the wall gets thicker.

2.2 Insulation Continuity 

Because double walls typically do not have exterior rigid insulation, the continuity of the 

insulation around the building shell must be carefully planned. The most critical intersections are 

the roof/wall connection and the slab/wall interface. If not detailed properly, thermal bypasses at 

these locations could result in condensation in the assemblies and potential moisture-related 

problems. 

2.2.1 Roof/Wall Connection

The detail in Figure 5 shows full-depth ceiling insulation extending to the outer edge of the 

double wall, which results in a significant reduction in thermal bridging. Combined with an 

airtight enclosure, this detail reduces the chances for condensation and heat loss at the top plates. 

However, different roof pitches may not allow for full-depth insulation for the entire depth of the 

double-wall cavity, as shown in Figure 6. To prevent thermal bridging in this area, a higher Rvalue insulation can be used to spot treat the area and bring it to the full R-value of the ceiling 

insulation. In Figure 7, ccSPF was used only over the outer edge of the wall to increase the Rvalue in that location. Cellulose insulation was then used for the remainder of the ceiling once 

the height of the rafter was high enough to accommodate the full depth desired. 

Figure 5. Roof/wall intersection showing good 

continuity of insulation

Figure 6. A shallow roof pitch resulting in the 

inability to install full-depth ceiling insulation 

over the entire depth of the wall cavity
8 

Figure 7. ccSPF installed over the outer edge of the double wall to the desired R-value for the 

ceiling

2.2.2 Slab/Wall Intersections 

In projects where double walls are being considered, it is likely that the foundation will be well 

insulated as well. Incorporating the slab edge insulation or exterior basement insulation into the 

design can be another challenge facing the construction team when double-wall construction is 

being implemented. Because double-wall plates do not hang over the foundation (they are flush 

with the concrete edge), the foundation rigid insulation ends up proud of the wall plane, which 

leads to potential water-management issues and thermal bypasses at the wall bottom plates. To 

accommodate this situation, the insulation should extend upward past the bottom plates and then 

be properly incorporated into the drainage plane. The detail in Figure 8 shows an example of 

how one project team incorporated the slab edge into a weather barrier impregnated on oriented 

strand board. 
9 

Figure 8. Flashing over slab edge insulation was taped to the sheathing using the manufacturer’s 

approved tape. The vented cladding was then attached with 3⁄4-in. furring strips, and it overlapped 

the flashing.

2.3 Durability and Moisture Issues

Both modeling and field studies have shown that temperatures of the exterior sheathing of walls 

without exterior rigid insulation are prone to increased chances for condensation from air 

exfiltration (Straube and Smegal 2009, Arena 2011, Arena 2014, Ueno 2015). The key steps to 

ensuring long-term durability of these types of wall structures include the following: 

• Ensure that the moisture content of the building materials remains < 12% during

construction.

• Implement meticulous air sealing.

• Install adequate mechanical ventilation to manage indoor relative humidity levels.

• Install a robust weather-resistant barrier.

• Provide a vented cladding system.

Because high R-value walls rely on drying to the interior as well as the exterior, an interior vapor 

barrier is generally not recommended. There are acceptable conditions under which elimination 

of the vapor barrier is allowed in the 2012 International Residential Code (IRC). Table R702.7.1 

in the 2012 IRC (reproduced in Table 2) lists the acceptable circumstance when a Class III vapor 

retarder (also called a latex paint) can be used. For marine Climate Zone 4 through Climate Zone

6, a Class III vapor retarder may be used if either a vented cladding is installed or the minimum 

level of insulating sheathing is installed. The insulating-sheathing requirement may be met by 

using the same R-value of 2-lb ccSPF on the interior side of the exterior sheathing. If interiorcavity 2-lb ccSPF is used in a hybrid high R-value wall, a vented cladding is still highly 

recommended.
10 

Table 2. 2012 IRC Requirements for Walls with a Class III Vapor Retarder

Climate Zone IRC 2012

Table R702.7.1 (Not Listed)

Marine 4

Vented cladding

• Wood sheathing product (oriented

strand board or plywood)

• Fiber board or

• Gypsum

Insulating sheathing 

• > = R2.5 for 2 x 4

• > = R3.75 for 2 x 6

5 

Vented cladding

• Wood sheathing product (oriented

strand board or plywood)

• Fiber board or

• Gypsum

Insulating sheathing 

• > = R5 for 2 x 4

• > = R7.5 for 2 x 6

6 

Vented cladding

• Fiber board or

• Gypsum

Insulating sheathing

• > = R7.5 for 2 x 4

• > = R11.25 for 2 x 6

7 

Insulating sheathing

• > = R10 for 2 x 4

• > = R15 for 2 x 6

If specifically required to install an interior Class I or Class II vapor retarder by your building 

department, consult an expert to perform a hygrothermal analysis, and make recommendations to 

the building officials based on that report. Insulation manufacturers often have recommendations 

for the types and placement of vapor retarders for their specific material, and they have been 

known to provide letters to the code officials to that effect if the code is in conflict with their 

recommendations. If absolutely necessary, chose a “smart” vapor retarder that becomes more 

vapor open as the relative humidity in the wall increases. These products are specifically 

designed to let the walls dry if they do get wet. 

2.4 Minimizing Disturbances of Insulation 

When an entire story of a home has a single 9-in. x 12-in. wall cavity filled with insulation, 

adding or repairing penetrations after the walls are insulated can seriously disrupt the insulation. 

In double-wall homes, careful planning for these penetrations is important, and all trades should 

be aware of the special requirements of the wall system. Because there are not discrete stud bays 

filled with insulation, it is good practice to install insulation netting or blocking around critical 
11 

wall penetrations. In this way, if a vent pipe must be accessed or repaired for any reason, 

insulation in the entire wall is not compromised; only insulation around the penetration must be 

replaced (see Figure 9).

Figure 9. Insulation netting surrounds vents and plumbing penetrations in an exterior double wall. 
12 

3 Technical Description

3.1 Applicable Wall Systems

As mentioned earlier, these guidelines have been created to help reduce the risk of moisturerelated damage with a particular focus on high R-value assemblies with no exterior rigid 

insulation installed over the exterior structural sheathing. Such assemblies include double-wall 

assemblies, Larsen trusses, and structural insulated panels. Although this guide focuses on 

double-wall framing, considerations and recommendations for moisture control, air sealing, and 

insulation apply to all wall assemblies without exterior rigid insulation.

3.2 Double-Wall Framing

A double wall consists of a load-bearing external frame wall usually constructed with 2 x 4 

framing at 16 in. on center. This wall is built and sheathed as a typical exterior frame wall. After 

the building is enclosed, an additional frame wall is constructed several inches inside the external 

load-bearing wall. 

This second wall can be constructed when interior framing begins, and it can be constructed of 2 

x 4 or 2 x 3 framing at 16 in. or 24 in. on center. Although 2 x 3 framing is often proposed for 

cost savings, it is challenging to find 2 x 3 lumber that is consistently square and straight. 

Because of this, most builders tend to use 2 x 4 framing for both the exterior and interior walls.

Although studies have shown that typical framing factors in homes (with studs at 16 in. on 

center) are near 25% (Carpenter 2003), with efficient framing techniques this framing factor can 

rather easily be reduced to 20%. Even lower framing factors are possible when moving to 24-in. 

stud spacing. 

Figure 10 through Figure 12 show examples of advanced framing techniques. Two-stud corners 

are very simple to implement on both the outer and inner framed wall because no drywall is 

attached to the outer wall, and no exterior sheathing is attached to the inner wall (Figure 10). 

Figure 10. Two-stud corners can be used for 

both the interior and exterior walls in the 

double-wall assembly.

Figure 11. Reduced framing around windows on 

the interior wall

Figure 11 and Figure 12 demonstrate reduced framing at the window and door openings that

results in increased wall insulation. On the inner wall, double top plates and jack studs are often 

Space between

the stud and 

sheathing allows

the insulation to 

be installed.
13 

not necessary (though jack studs may still be used for more consistent alignment of window 

openings). Finally, ladder framing can be used to attach interior partition walls to exterior walls

to further reducing framing. 

Figure 12. Reductions in framing around the

openings allows for more insulation in headers.

Such advanced framing strategies are encouraged because they can certainly save framing 

material and labor, but because of the thermal break between the two walls, reducing the framing 

does not dramatically increase the thermal resistance of the wall system (see Table 3).

Additionally, because of the substantial thermal break between the walls, there is also very little 

thermal impact when the inner and outer studs are aligned compared to staggered-stud 

configurations. 

Table 3. Thermal Effects of Framing Factors on Double Walls

Framing Factor Whole-Wall R-Value 

(ft2 h °F/Btu)

16% 35

20% 34

25% 33

Before the windows and doors are set, the rough openings must be boxed out with sheathing, 

lumber, or drywall, as shown in Figure 13, to provide blocking between the two walls for the 

insulation that will typically be blown or sprayed into the wall cavity. Sloping the window sill 

toward the exterior or providing a window dam on the interior side of the window to prevent 

water intrusion is highly recommended. 
14 

Figure 13. Windows in double walls: (left) a framed window opening and (right) a set window

3.3 Electrical and Plumbing

Electrical rough-in in double walls can be slightly simplified because the wires can be run

between the two framed walls making drilling unnecessary. Electrical boxes are normally

installed on the interior wall. Plumbing and mechanical penetrations through the exterior walls 

should be blocked off or netted before the insulation is installed to minimize disturbance to the 

insulation if repairs or service are needed at these locations in the future. 

3.4 Air Barriers

As with any high-performance wall system, air sealing is critical. Before insulating, meticulous 

caulking and/or foaming of the exterior sheathing, top and bottom plates, penetrations, etc., is 

strongly advised. Interior or exterior air barriers (Figure 14 and Figure 15) are acceptable, and 

each has pros and cons. 

Figure 14. Interior air barrier with all seams 

taped

Figure 15. Exterior air barrier with all seams 

taped

3.4.1 Interior Air Barriers

As shown in Figure 14, the interior surface of the wall can be used as the airtight layer in a 

double-wall home. However, because the electrical boxes and some plumbing vents run in the 

exterior walls, creating a significantly airtight barrier can be difficult. A typical approach is to 
15 

install a sheathing product on the interior of the double wall and then fur out a small chase wall 

where the electrical and plumbing runs can be housed without actually penetrating the air barrier.

The pros and cons of this approach include: 

• Pros

o It is easy to connect the wall airtight layer to the ceiling airtight layer.

o There is no need to test the airtight layer twice; only once after the insulation is

sufficient to ensure goals have been met.

o This approach prevents convective looping if high and low air leaks are present

on the interior of the envelope.

• Cons

o It is more difficult to tie in the airtight layer of the foundation.

o There is an additional cost of the second layer of sheathing and additional labor to

install the interior chase wall.

3.4.2 Exterior Air Barriers

One method for implementing an exterior airtight layer is shown in Figure 15. Tape is used to 

seal all seams and corners in the structural sheathing whether it is oriented strand board, 

plywood, or an impregnated weather-resistant barrier. Sheet weather barriers applied on top of 

the structural sheathing can also act as the air barrier and will need to be taped and incorporated 

in the rest of the airtight layer in the same way as the sheathing. All connections to the window 

and door openings must be taped, all penetrations must be sealed, and the sheathing must be tied 

in to the ceiling and foundation air barriers. Pros and cons of this method include: 

• Pros

o It is easy to connect the wall airtight layer to the foundation airtight layer.

o It is easy to inspect, and there are fewer jogs in the airtight layer.

o There is no extra cost for an interior chase wall; the interior is simply netted for

cellulose, and all electrical and plumbing penetrations are handled normally.

• Cons

o It is more difficult to tie in the airtight layer of the ceiling.

o Using sheet weather barriers as the airtight layer can be more labor intensive than

using the structural sheathing.

o The airtight layer should be tested twice, once the air barrier is in place before the

insulation is installed and once after the insulation but before the drywall.

3.5 Insulation

After rough-in and air sealing, the wall cavities can be filled with insulation.

3.5.1 Single Insulation Strategy

Full-depth cellulose, fiberglass, or ocSPF can be used to fill the entire wall. When installing 

cellulose or fiberglass, insulation netting or a reinforced vapor retarder (when a vapor retarder is 
16 

required) is usually installed on the inside of the interior framing. Aside from the added 

insulation material, the time to install the blown insulation is slightly higher. However, the 

considerable preparation time (primarily installing netting for blown insulation) is very similar to 

time required when blowing a conventional framed wall. For example, the additional time 

needed to insulate 800 ft2

 of a 12-in. double wall with dense-blown cellulose (when compared to 

insulating a single 2 x 6 wall with blown cellulose) is approximately two person-hours. The total 

incremental cost is approximately 30%; additional insulation material accounts for most of this 

cost (Tauer 2009, Perkins 2009). 

The method of blowing insulation is somewhat different than it is in single-frame construction.

Because the wall is not divided into discrete stud bays, the exterior walls for each story basically 

include one large insulation cavity. When using dry, dense-blown insulation, insulators typically 

fill this cavity by moving around the home in a circular pattern; each section of the wall is 

partially filled. After the walls are nearly completely filled, the insulator makes one more circuit 

around the home blowing through each interior stud bay until the insulation reaches the desired 

density (Tauer 2009). 

Figure 16. Double wall before and after insulation with dense-blown cellulose

As noted, ocSPF can also be used in the entire cavity. The cost of the material is generally 

higher, but there is a trade-off because no netting is required, and the entire cavity can be filled 

immediately without making circular passes around the home. This labor savings can make this 

method of insulation cost-competitive with loose-fill insulation.

Because the gap between the two walls is filled completely with insulation, there is no thermal 

bridge through the wall system. This is shown in Table 4, and this thermal break results in 

whole-wall R-values very close to nominal R-values. 
17 

Table 4. R-Values for Double Walls of Varying Thicknesses

Space Between

2 x 4 Walls

Total 

Insulation 

Depth

R-Values* (ft2 °F hr/Btu)

Nominal Whole-Wall 

1 in. 8 in. 30 26

2 in. 9 in. 33 30

3 in. 10 in. 37 34

5 in. 12 in. 44 42

* Values are based on R-3.7 per inch of dense-packed cellulose insulation.

3.5.2 Hybrid Insulation Strategy

A common option when combining insulation products is ccSPF. Not only does it have a higher 

R-value/inch compared to other insulation types, it also provides a vapor retarder. This hybrid

insulation strategy can be useful when floor space is at a premium and wall thickness cannot be

increased but a higher wall R-value is desired. If using a combination of products, proper

attention must be paid to the ratio of air-impermeable insulation (ccSPF) to air-permeable

insulation (fiberglass, cellulose, ocSPF) or condensation problems could occur. Refer to Table

R702.7.1 in the 2012 IRC to determine the proper ratio. Divide the required wall R-value for

your climate zone by the minimum R-value of the insulating sheathing to determine the ratio of

impermeable to permeable insulation. Multiply the desired R-value for the high R-value wall by

this ratio, and divide by the R-value per inch of the impermeable insulation. This will tell you

how many inches of impermeable insulation you will need for your assembly.
18 

3.6 Moisture-Management System

Because high R-value walls dry more slowly than conventional construction, attention to the 

moisture management of the façade is even more critical. Wood components must be properly 

separated from the masonry and protected from bulk water leaks by a robust weatherExample: Determine (1) the minimum thickness of the air-impermeable insulation for a 

double wall in Climate Zone 6 that will be insulated with cellulose and ccSPF, (2) the 

thickness of the cellulose, and (3) the total thickness of the wall. The desired R-value of 

the assembly is R-50 minimum.

ccSPF ≈ R-6.5/in. 

cellulose ≈ 3.6/in. 

Answer 1: ccSPF thickness 

Step 1. Determine the proper ratio of impermeable insulation needed. 

Table 702.7.1 states that a minimum R-value of 7.5 ft2∙°F∙hr/Btu is required for a 

2 x 4 wall. The total R-value requirement for a 2 x 4 in that climate is R-21. 

Therefore, the ratio of impermeable ccSPF to permeable cellulose would be 

R-7.5 ÷ R-21 = 36%.

Step 2. Determine the minimum R-value of ccSPF needed in an R-50 assembly in 

Climate Zone 6.

R-50 x 0.36 = R-18

Step 3. Determine the number of inches of ccSPF needed in an R-50 assembly in Climate 

Zone 6 

R-18 ÷ R-6.5/in. = 2.8. A 3-in. minimum should be specified.

Answer 2: Cellulose thickness 

Step 1. Determine the remaining R-value needed.

R-50 – R-18 = R-32 needed

Step 2. Determine the thickness of the cellulose 

R-32 ÷ 3.6/in. = 8.8, 9 in. of cellulose needed.

Answer 3: Total wall thickness

3 in. of ccSPF + 9 in. of cellulose = 12-in. wall depth

Space between the two walls = 12 in. – (2 x 3.5-in.studs) = 5-in. gap needed. 
19 

management system. Avenues for drying through-vented claddings must also be provided in case 

water does make its way into the assembly. Finally, preventing warm, moist air from entering the 

façade must be accomplished through diligent air sealing and by controlling interior moisture 

levels.

3.6.1 Capillary Breaks

A capillary break should be installed between the concrete foundation and the wall components 

for the entire depth of the wall to prevent foundation moisture from being wicked up by the 

building materials. Figure 17 shows an incomplete capillary break that was installed only under 

the exterior bearing wall’s bottom plate. The break should span the entire depth of the wall so 

that both walls and the insulation will be separated from the concrete. 

Figure 17. Incomplete capillary break. It should be installed the entire depth of the wall to keep 

lumber and insulation from wicking up moisture. 

3.6.2 Water-Resistive Barriers

The water-resistive barrier (WRB) for a double-stud wall is no different than that for 

conventional framing. The options include building wraps, liquid-applied membranes, and 

impregnated sheathings (see Figure 15 under the Air Barriers section) that come from the factory 

with the WRB applied directly to the structural sheathing. However, attention to detail is far 

more critical because high R-value assemblies dry more slowly than standard construction. Bulk 

water leaks could result in much more damage in a high R-value wall because the materials 

could remain wet for longer periods of time, which increases the potential for mold growth and 

decay. No matter which method is used, the installation must be robust, and the product should 

be vapor open to allow for drying to the exterior. Products greater than 10 perms are 

recommended by the author. 

Capillary break

Incorrect: No 

capillary break
20 

Figure 18. Example of a building wrap being 

used for the WRB

Figure 19. Image of liquid-applied WRB

3.6.3 Cladding

To aid in drying the assembly, particularly the exterior sheathing, a ventilated cladding is highly 

recommended. Figure 20 and Figure 21 show examples of attachments for two different types of 

siding: horizontal fiber cement boards and corrugated metal panels. A ventilated cladding

system, also often referred to as a rain screen, in conjunction with vapor-open materials on both 

the interior and exterior of the wall assembly, result in the best drying potential for high R-value 

walls without exterior rigid insulation.
21 

Figure 20. Vertical furring strips create a vent 

space for horizontal fiber cement siding. 

Figure 21. Horizontal furring was used to attach

a corrugated metal panel siding that allows 

vertical draining and venting of the sheathing.

3.6.4 Mechanical Ventilation

The durability of high R-value walls is highly dependent on controlling the exfiltration of the 

interior air through the building envelope as well as controlling the moisture inside the building. 

If the interior air can enter the wall cavity, the potential for condensation on the colder surfaces 

on the interior of the wall assembly increases as the moisture levels in the home increase.

Control of the interior air moisture levels must be achieved through proper ventilation. The level 

of ventilation will depend on the number of occupants, pets, plants, and other sources of moisture 

in the home. 

Continuous mechanical ventilation should be installed in every high-performance home. In cold 

climates, heat- or energy-recovery ventilation is recommended to reduce energy use and to 

ensure that air entering the home does not create cold spots and discomfort. Methods to reduce 

fan noise from the ventilation system should also be employed as should techniques for reducing 

vibration noise. The goal is to minimize the chances that the system will be turned off due to 

comfort or noise issues. 

A method to increase the continuous ventilation level should also be provided so that the 

occupants can remove unusually high levels of moisture as needed. These instances may result 

from cooking, bathing, an unusually high number of occupants, etc. Manual boost controls or 

humidity sensors can be used. Regardless of how this is achieved, indoor relative humidity levels 

during the winter months should be kept between 30% and 40%. 
22

4 Measure Implementation

4.1 Climate-Specific Factors

This guide is intended for use in Climate Zones 5 and higher. Cold climates that also experience 

hot-humid summers are the primary targets because they are less forgiving than cold-dry 

climates with respect to drying the high R-value assemblies. However, the information contained 

here is still applicable but not as critical.

4.2 Field Inspection

To ensure that assemblies are constructed in a durable manner, pre-insulation air-leakage testing,

pre-drywall insulation inspections, and pre-drywall air-leakage testing are highly recommended.

Preventing exfiltration of the interior air into the wall assembly during the cold months is crucial 

for moisture control.

4.3 Install Procedure

Following is a sequential layout of the steps required to build an airtight, water-managed, high 

R-value wall assembly using double-wall construction. Details for all typical junctions have been 

provided. This guide assumes that all components of the building envelope are high performance 

and super insulated.
23 

4.4 Foundation Details

Double-wall construction can be used independent of the foundation type chosen. Details for 

basement, crawl space, and slab-on-grade applications are provided below. Proper placement of 

the vapor-control layer and alignment of the foundation insulation are the critical steps at this 

stage. The red dashed line indicates the combined air/water-resistive barrier.

Foundation: Basement/Crawl Space

Notes:

1. Spray foam in the rim joist provides

continuous air and a thermal barrier between

framed wall and the foundation.

2. The thermal value of the spray foam

should match thermal value of the framed

wall.

3. A capillary break is required between the

foundation and wood components.

Foundation: Slab-on-Grade—Interior 

Insulation Placement

Notes:

1. Sill seal prevents the foundation moisture

from wicking into the wall cavity. Install for

full depth of the wall cavity and underneath

both bottom plates. Use a liquid-applied

water barrier at the bottom of the wall if the

width exceeds the available sill seal products.

2. The interior stud wall sits on the slab,

concealing the insulation between the slab

and the stem wall.
24 

Foundation: Slab-on-Grade—Exterior 

Insulation Placement

Notes:

1. Install a vapor barrier under the slab,

vertically on the interior of the stem wall,

under the footing, and up the exterior of the

stem wall to the top of the grade.

2. Extend the insulation upward past the

bottom plate to reduce the thermal bridge.

3. Install the insulation under the slab and

vertically on the interior of the stem wall.
25 

4.5 Wall Framing

After the proper moisture-control strategies have been installed at the foundation level, wall 

framing can begin. The exterior load-bearing wall will be constructed first. The builder has the 

flexibility to decide if the second wall is installed next or if it is installed after the building is 

dried in. The following details are independent of that sequencing. 

Typical Wall 

Notes: 

1. The inner and outer wall framing are typically

framed with 2 x 4s at 16 in. on center. The inner

and outer wall studs do not need to be offset.

2. The distance between the inner and outer wall

framing varies depending on the desired R-value.

Overall depth typically does not exceed 16 in.

(Refer to the insulation manufacturer’s installation

guidelines.)

3. Air/water barrier options

a. Rolled sheet, mechanically fastened

b. Rolled sheet, self-adhering

c. Liquid-applied

d. Impregnated sheathing

4. Vented cladding options

a. Wood, cement board, etc., on furring (shown)

b. Vinyl siding
26 

Exterior Corner 

Notes:

1. Avoid unnecessary framing at the exterior

corners.

2. California corner drywall support options:

a. 1 x 4 nailer (shown)

b. Drywall clips

4.6 Roof Connection

Either a vented attic or a cathedral ceiling can be constructed in conjunction with double-wall 

construction. Continuity of the air barrier must be achieved with either construction method; 

however, high R-value vented roof assemblies are simpler from a moisture-management 

perspective.

Roof/Wall Connection: Unconditioned 

Attic

Notes:

1. A raised heel truss allows for full-depth

ceiling insulation at the outer edge of the

wall.

2. Sheathing is installed over the top plates to

provide blocking for blown-in insulation and

to connect the exterior airtight layer on the

wall to the airtight layer under the ceiling.

3. A sheathing sealant at top of the inner and

outer wall framing connects the airtight

layers. Air barrier tapes are recommended

instead of caulk.
27 

4.7 Rim/Band Joist Details

No special framing techniques are required to accommodate double walls at the rim/band joist; 

however, additional blocking will be required if cellulose or fiberglass insulation will be blown 

into the rim.

Rim/Band Joist: Dense-Packed Insulation

Notes:

1. Horizontal sheathing between the inner

and outer wall framing prevents densepacked wall insulation from migrating into

floor cavity during insulation.

2. Blocking provides a fastening surface for

the netting.

3. The thermal value of the rim insulation

should match the thermal value of the framed

wall.

Rim/Band Joist: Spray Foam Insulation 

Notes:

1. The horizontal sheathing between the inner

and outer wall framing prevents the

insulation from migrating into the floor

cavity during insulation.

2. No additional blocking is required if spray

foam is used.

3. The thermal value of the rim insulation

should match the thermal value of the framed

wall

4.8 Windows and Doors

Windows can be installed flush with the exterior structural sheathing to make incorporating them 

into the drainage plane simple. They can also be installed in the center of the wall to improve the 

thermal performance of the frame. Thermal modeling has shown little advantage to moving them 

all the way to the interior compared to locating them in the center.

1 Doors must be installed at 

1 See http://www.passivhausplaner.eu/MusterPH_Projektdoku_Bild/passivhaus_Butcher_Butcher_DenbyDale.pdf. 
28 

the interior edge of the framing to allow for full operation unless detailed to allow for a swing 

greater than 90°. In either case, moisture-management details must be clearly identified on the 

plans and executed as such during installation to reduce the potential for bulk water leaks. 

Window Head: Exterior 

Placement

Notes:

1. Window frames are taped to

the exterior sheathing on the top

and sides.

2. The interior edge of the

window frames is taped to the

window opening with splitbacked tape.

Window Sill: Exterior 

Placement

Notes:

1. Window frames are taped to

the exterior sheathing on the top

and sides.

2. A backer rod and caulk are

used under the frame to provide a

water-tight and airtight seal.

3. The interior edge of the

window frames are taped to the

window opening with splitbacked tape.

4. Slope the sill to the exterior.

5. If the window is installed with

clips, tape over the entire length

of the clip.
29 

Window Jamb: Exterior 

Placement

Notes:

1. Window frames are taped to

the exterior sheathing on the top

and sides.

2. Split-backed tape can be used

around the entire frame to seal it

around the perimeter.

Window Head: Interior 

Placement

Notes:

1. Window frames are taped to

the opening on the top and sides

on the exterior.

2. Split-backed tape can be used

around the entire frame on the

interior to seal it around the

perimeter.
30 

Window Sill: Interior 

Placement

Notes:

1. Window frames are taped to

the opening on the top and sides

on the exterior.

2. A backer rod and caulk are

used under the frame to provide a

water-tight and airtight seal.

3. Split-backed tape can be used

around the entire frame on the

interior to seal it around the

perimeter.

4. Slope the sill to the exterior.

Window Jamb: Interior 

Placement

Notes:

1. Window frames are taped to

the exterior sheathing on the top

and sides.

2. Split-backed tape can be used

around the entire frame on the

interior to seal it around the

perimeter.
31 

Door Head and Sill

Notes:

1. The door sill is difficult to seal.

Use a backer rod and caulk when

possible.

2. Tape the door jambs to the

opening on the interior and

exterior.

Door Jamb

Notes:

1. Special detailing is needed if

the door is not mounted flush

with the interior framing.
32 

4.9 Weather-Resistive Barrier

As noted above, the WRB can be a building wrap, liquid applied, or impregnated onto the 

structural sheathing at the factory. Depending on which method is being used, various steps in 

the following sequence can be eliminated. These have been indicated in the notes. 

Note: If using liquid-applied or impregnated 

WRB, skip to Step 3. 

Step 1. (House wrap only) Install house wrap. 

a. Tape all seams with manufacturerrecommended tape.

b. Cut at the window opening, as shown.

Note: If using liquid-applied or impregnated 

WRB, skip to Step 3. 

Step 2a. (House wrap only) Fold house wrap 

around opening. 

a. Fold wrap into the interior of the home at the

sill and jambs. Tack in place.

b. Fold wrap at the header up and to the

exterior. Temporarily tack or tape out of the

way.
33 

Interior-Mount Window/Door Only

Step 2b. Install blocking at sill. 

Exterior-Mount Window/Door

3A. Install flexible flashing sill pan to horizontal sill, 

wrapping up onto vertical wall surface. Note: Applies to all 

WRBs. 

Interior-Mount Window/Door

3B. Install flexible flashing sill pan to 

horizontal sill, wrapping up onto vertical wall 

surface. Note: Applies to all WRBs.
34 

Interior-Mount Window/Door Only

3C. Install flexible flashing to the sides of the 

window opening, wrapping over sill pan. 

Exterior-Mount Window/Door

4A. Install window. 

Interior-Mount Window/Door

4B. Install window. 
35 

5A. Install 4-in. flashing tape at jambs spanning from

the window frame to the WRB.

a

 

a Alternatively, split-back flashing tapes may be attached to the

window before installation. Once installed, the second backing is 

removed from the tape and attached to the WRB. 

5B. Tape window jambs to WRB.

b

b Alternatively, split-back flashing tapes may be attached to

the window before installation. Once installed, the second 

backing is removed from the tape and attached to the WRB. 
36 

6A. Install 4-in. flashing tape at the head spanning from

the window frame to the moisture barrier. 

6B. Install 4-in. flashing tape at the head spanning 

from the window frame to the moisture barrier. 

4.10 Insulation

Before the insulation is installed, ensure that the exterior wall penetrations have been boxed out 

to prevent disruption to the insulation should repairs or access be needed in the future. All 

exterior wall penetrations should be air sealed at this time regardless of whether the airtight layer 

is on the exterior or interior of the wall. 

If the airtight layer will be on the exterior, all seams and penetrations should be taped and sealed 

before the insulation is installed. All connections to the foundation, roof, and wall corners should 

also be airtight at this time. An air-leakage test before the insulation is installed is highly 

recommended to ensure that the airtight layer is meeting the project goals. Repairs, if necessary, 

will be easiest before the insulation is installed. 

After the air sealing is complete, the insulation can be installed. A single type or a combination 

of types can be used. Refer to the insulation ratios discussed in Section 3: Technical Description

to determine the proper levels of air-impermeable and air-permeable insulation if a hybrid 

strategy is desired.
37 

Hybrid Insulation Strategy: ccSPF +

Cellulose

Notes:

1. Do not rely on spray foam to meet

airtightness requirements. It will not air seal

critical leaks at the roof/wall and slab/wall

connections.

2. Check Table R702.7.1 of the 2012 IRC for

the proper ratio of impermeable to permeable

insulation for the project’s climate zone.

3. Do not install an interior vapor

barrier/retarder if using ccSPF. The foam will

act as a vapor retarder; having a vapor

retarder on both sides of the wall risks

trapping moisture.

Full Depth Insulation: Cellulose, 

Fiberglass, ocSPF 

Notes:

1. Check your local code and product

manufacturer for vapor barrier/retarder

requirements.

2. If a vapor barrier/retarder is necessary,

install a product that will become more vapor

open as the interior wall relative humidity

increases. These are often referred to as

“smart” vapor retarders.

4.11 Drywall

If an interior airtight layer is being installed instead of one on the exterior, it must be installed 

before the drywall. Because of the number of electrical penetrations on an interior wall, it is not 

recommended that the electrical outlets or switch plates be installed on the interior stud wall of 
38 

the double-wall assembly. Instead, sheathing should be installed on the interior side of the 

interior wall and taped and sealed at any necessary plumbing and electrical penetrations. A 

separate chase wall should then be constructed on the interior of the double wall and all electrical 

boxes installed in that space. Airtightness testing should be conducted after the interior sheathing 

has been sealed and incorporated into the ceiling and foundation airtight layers. After the project 

goals have been achieved, the drywall can be installed. 

4.12 Cladding Attachment

Ventilated cladding is required by code if a Class I or Class II vapor retarder is not installed on 

the interior of the wall in Climate Zones 5 and higher. It is recommended that vapor retarders not 

be installed on high R-value walls so that the walls can dry to both the interior and the exterior. 

For this reason, vented claddings are highly recommended when high R-value wall assemblies 

are constructed in cold climates. If needed, a smart vapor retarder that becomes more open as the 

humidity increases is recommended. However, a vented cladding is still recommended.

Exterior Mount

1. Install flashing at head.

Interior Mount

1. Install flashing at head.
39 

Exterior Mount

2. Install furring strips.

Interior Mount

2. Install furring strips.

3. Install window trim and integrated flashing at sill. 3. Install window trim and integrated flashing at sill.
40 

Exterior Mount

4. Install cladding.

Interior Mount

4. Install cladding.
41 

5 Verification Procedures and Tests

In addition to visual inspections to verify air-sealing measures and proper installation of the 

insulation, two tests should be conducted on every high-performance home. The first is a blower 

door test to verify that the airtight layer meets the projects goals. The second is testing the 

ventilation system to ensure that flow rates are as specified and that the system is balanced.

5.1 Air-Leakage Testing

Air-leakage testing is a good idea on any construction project, but it is essential on a home that 

has high R-value walls to ensure that the wall assembly is airtight. The goal is to prevent warm 

interior air from entering the wall cavity during the cold periods of the year. This warm air can 

condense on colder exterior surfaces inside the wall cavity, and over time it can cause moisturerelated problems such as mold growth and decay. 

Blower door testing is used regularly on energy-efficient projects throughout the United States. 

Trained professionals are located in every state. Section N11024 of the 2012 IRC requires that all 

new construction be blower door tested, and many states and municipalities have begun 

mandating this testing.

The basic equipment consists of a door frame, a sheet to cover the frame, a fan to pressurize or 

depressurize the home, and gauges to measure the flow through the fan. Typically 

depressurization tests are run because it is easier to detect the location of the leaks from inside 

the home. It is recommended that homes with high R-value walls be tested before the insulation 

is installed and then again before the drywall is installed. Waiting until construction is complete 

could result in the inability to fix problematic air leaks.

Figure 22. Typical blower door equipment used to detect air leakage through the building 

envelope

Sheet

Fan

Gauge (manometer) 

Frame
42 

5.2 Ventilation System Balancing and Commissioning

In addition to blower door testing, it is highly recommended that the 

mechanical ventilation system be tested and balanced. Although 

exhaust-only ventilation has been shown to work, it is highly 

recommended that super-insulated, airtight homes incorporate 

continuously balanced mechanical ventilation. Stale, moist indoor air 

must be removed and replaced with fresh outdoor air. A balanced heatrecovery ventilation system performs both these tasks and significantly 

reduces the amount of energy lost from the outgoing airstream. 

However, if these systems are not balanced—incoming air and 

outgoing air flows are within 10% of each other—moisture removal 

and heat exchange can be compromised, and interior humidity could 

reach undesirable levels.

To prevent this, the incoming and outgoing airstreams at the ventilation unit should be measured 

and adjusted if they are more than the 10% different. Low-flow balometers or power-capture 

hoods can be used to measure the flow rates. The air flow at each of the supply and return 

registers should also be measured to verify that the amount of air being exhausted and supplied 

to the various rooms is as designed. 

Heat-recovery 

ventilator/energyrecovery ventilator 

ductwork must be 

well sealed with 

mastic. A balanced 

system is less likely 

to be achieved if the 

 
43 

References

Aldrich, R., Arena, L., and Zoeller,W. 2010. Practical Residential Wall Systems: R-30 and 

Beyond. Best Conference Proceedings, 2010, Clearwater, FL. 

Arena, L. 2014. The Hygrothermal Performance of an R-40 Cellulose Wall in Climate Zone 5A. 

(Building America Technical Report.) Washington, DC: U.S. Department of Energy. 

Carpenter S.C., and Schumacher C. 2003. Characterization of Framing Factors for WoodFramed Low-Rise Residential Buildings. ASHRAE Transactions. Vol. 109, Pt. 1 (February), pp. 

101-108.

Perkins, Anne. Director of Homeownership Programs, Rural Development, Inc. Personal 

conversation. October 2009. 

Straube, J., and J. Smegal. 2009. Building America Special Research Project: High-R Walls 

Case Study Analysis. (Technical Report RR-0903.) Somerville, MA: Building Science 

Corporation. 

Tauer, Jonathan. President, Celluspray Insulation. Personal conversation. October 2009. 

Ueno, K and Straube, J . 2008. Laboratory Calibration and Field Results of Wood Resistance 

Humidity Sensors. BEST 1 Conference. 
44 

Appendix A: Compliance with U.S. Department of Energy Zero 

Energy Ready Home Criteria

Area of Improvement Mandatory Requirements

Envelope  Ceiling, wall, floor, and slab insulation shall meet or exceed 

2012 IECC levels 

ENERGY STAR® Version 3 (Rev. 07) compliance 

Water Management System Builder Checklist 

1. Water-Managed Site and Foundation

1.3 Capillary break beneath all slabs (e.g., slab on grade, basement slab) except 

crawlspace slabs using either: ≥ 6 mil polyethylene sheeting, lapped 6-12 in., or ≥ 1 in. 

extruded polystyrene insulation with taped joints. 

1.5 Continuous drainage plane behind exterior cladding, properly flashed to foundation 

(WMS 2.2) 

1.6 Window and door openings fully flashed (WMS 2.3) 

1.13 Materials with signs of water damage or mold (WMS 4.5) 

Thermal Enclosure System Rater Checklist

2. Quality-Installed Insulation

2.1 Ceiling, wall, floor, and slab insulation levels shall: 

2.1.1 Meet or exceed 2009 IECC levels 

2.2 All ceiling, wall, floor, and slab insulation shall achieve RESNET-defined Grade I 

installation or, alternatively, Grade II for surfaces that contain a layer of continuous, airimpermeable insulation ≥ R-5 in Climate Zones 5 to 8

3. Fully- Aligned Air Barriers

3.1 Walls

3.1.1 Walls behind showers and tubs 

3.1.3 Attic knee walls

4. Reduced Thermal Bridging

4.1 For insulated ceilings with attic space above (i.e., non-cathedralized), Grade 1 

insulation extends to the inside face of the exterior wall below at these levels: CZ 1–5: ≥ 

R-21; CZ 1–5: ≥ R-21

4.4 Reduced Thermal Bridging at above-grade walls

4.4.4 Double-wall framing

4.4.5 Advanced framing

4.4.5a All corners insulated ≥ R-6 to edge 

4.4.5b All headers above windows & doors insulated >= R-3 for 2×4 

framing or equivalent cavity width 

4.4.5c Framing limited at all windows and doors to one pair of king studs, 

plus one pair of jack studs per window opening to support the header and 

sill
45 

4.4.5d All interior/exterior wall intersections insulated to the same R-value 

as the rest of the exterior wall 

5. Air Sealing

5.1 Penetrations to unconditioned space fully sealed with solid blocking or flashing as 

needed and gaps sealed with caulk or foam 

5.1.1 Duct/flue shaft 

5.1.2 Plumbing/piping 

5.1.3 Electrical wiring

5.2 Cracks in building envelope fully sealed

5.2.1 All sill plates adjacent to conditioned space sealed to foundation or subfloor 

with caulk, foam, or equivalent material. Foam gasket also placed beneath sill 

plate if resting atop concrete or masonry and adjacent to conditioned space 

5.2.3 Drywall sealed to top plate at all unconditioned attic/wall interface using 

caulk, foam, drywall adhesive (but not other construction adhesive), or equivalent 

material. Either apply sealant directly between dry wall and top plate or to the 

seam between the two from the attic above. 

5.2.4 Rough opening around windows & exterior doors sealed with caulk or foam 

HVAC System Quality Installation Contractor Checklist

1. Whole-Building Mechanical Ventilation Design

1.1 Ventilation system installed that has been designed to meet ASHRAE 62.2-2010 

requirements including, but not limited to, requirements in Items 1.2-1.5. 
DOE/GO-102016-4783 ▪ July 2016

buildingamerica.gov

For more information, visit: energy.gov/eere