BUILDING TECHNOLOGIES PROGRAM

R

Retrofit Techniques & Technologies:

Air Sealing

A Guide for Contractors 

to Share with Homeowners

PREPARED BY

Pacific Northwest National Laboratory 

& Oak Ridge National Laboratory

April 12, 2010

April 12, 2010 • PNNL-19284

VOLUME 10. Building America Best Practices Series
Building America Best Practices Series

Retrofit Techniques and Technologies:

Air Sealing

A Guide for Contractors to Share with Homeowners

Prepared by

Pacific Northwest National Laboratory

Michael C. Baechler

Theresa Gilbride, Marye Hefty, Pam Cole, and Jennifer Williamson

and 

Oak Ridge National Laboratory

Pat M. Love

April 12, 2010

Prepared for the U.S. Department of Energy

under Contract DE-AC05-76RLO 1830

PNNL-19284

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 Battelle Memorial Institute, 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, or Battelle Memorial Institute. The views and 

opinions of authors expressed herein do not necessarily state or reflect those of 

the United States Government or any agency thereof.
Preface

The U.S. Department of Energy recognizes the enormous potential 

that exists for improving the energy efficiency, safety, and comfort 

of existing American homes. This series of Retrofit Techniques and 

Technologies describes approaches for homeowners and builders 

working on existing homes. This guide will help homeowners identify 

ways to make their homes more comfortable, more energy efficient, 

and healthier to live in. It also identifies the steps to take, with the 

help of a qualified home performance contractor, to seal unwanted 

air leaks while ensuring healthy levels of ventilation and avoiding 

sources of indoor air pollution. Contractors can use this document to 

explain the value of these air sealing measures to their customers. The 

references in this document provide further explanation of air sealing 

techniques and technologies.

Studies show that the measures described in this guide can typically 

achieve whole-house energy savings of 10% to 20% over pre-retrofit 

energy usage. In older homes or homes with greater levels of air 

leaks, savings may be much higher.

These practices are based on the results of research and 

demonstration projects conducted by the U.S. Department of 

Energy’s Building America and Home Performance with ENERGY 

STAR sponsored by the U.S. Environmental Protection Agency 

and DOE. Home Performance with ENERGY STAR offers a 

comprehensive, whole-house approach to improving the energy 

efficiency and comfort of existing homes and requires a test-in/

test-out to test combustion products (www.energystar.gov/

homeperformance).

DOE’s Building America has worked with some of the nation’s 

leading building scientists and more than 300 production builders on 

over 41,000 new homes. Building America’s research applies building 

science to the goal of achieving efficient, comfortable, healthy, and 

durable homes. 

Please submit your comments via e-mail to: 

George James (George.James@ee.doe.gov) 

You can learn more about Building 

America and download additional copies 

of this document, other best practices, 

research reports, and case studies at 

www.buildingamerica.gov

R

i April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Contents

Preface .............................................................. i

Introduction........................................................ 1

Finding a Contractor .............................................. 3

Test In/Test Out .................................................... 4

Step 1. The Audit ................................................ 4

Step 2. Installing Air Sealing Measures ........................ 5

Step 3. Testing Out.............................................. 5

Diagnostic Tools Used During Test-In Test-Out .................. 6

Safety and Health Issues .......................................... 7

Ventilate it Right ................................................... 8

New Code Air Sealing Requirements ............................. 9

An Air Sealing Checklist .......................................... 10

1. Air Barrier and Thermal Barrier Alignment ............... 12

2. Attic Air Sealing............................................. 13

3. Attic Kneewalls............................................. 14

4. Duct Shaft/Piping Shaft and Penetrations................ 15

5. Dropped Ceiling/Soffit .................................... 16

6. Staircase Framing at Exterior Wall/Attic .................. 17

7. Porch Roof ................................................. 18

8. Flue or Chimney Shaft..................................... 19

9. Attic Access/Pull-Down Stair ............................. 20

10. Recessed Lighting .......................................... 21

11. Ducts ....................................................... 22 

12. Whole-House Fan Penetration at Attic................... 24

13. Exterior Walls .............................................. 25

14. Fireplace Wall .............................................. 26

15. Garage/Living Space Walls ............................... 27

16. Cantilevered Floor ......................................... 29

17. Rim Joists, Sill Plate, Foundation, and Floor ............. 30

18. Windows and Doors ....................................... 32

19. Common Walls Between Attached Dwelling Units...... 33

April 12, 2010 ii

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Introduction

Imagine opening a window in your house and leaving it that way 

24 hours a day, all year long. On balmy spring days, the breeze wouldn’t 

be so bad. But, in the freezing cold of winter and the sticky heat of 

summer, with the furnace or air conditioner on, smart homeowners 

would recognize they might as well be throwing buckets of quarters 

out the window to pay for the escaping heated or cooled air.

Air leaks in most existing homes add up to an open window in your 

home. Air sealing is one of the least expensive and most cost-effective 

measures you can take to improve your home’s comfort and energy 

efficiency. By sealing uncontrolled air leaks, you can expect to see 

savings of 10% to 20% on your heating and cooling bills, and even 

more if you have an older or especially leaky 

house. But, before you grab your caulk gun, 

there are some things you should consider.

Many older homes lack proper ventilation, so 

they depend on those cracks and leaks to let in 

air, especially when fuel-burning appliances are operating inside the 

home. Without ventilation, carbon monoxide and air pollutants from 

cleaning chemicals, combustion appliances, and off-gassing household 

products can build up, creating an unhealthy and even dangerous 

environment in the home. Opening windows is one way to ventilate, 

but there are times when opening the windows is not practical (e.g., it 

is too cold or too hot outside). Fortunately there are other options 

for bringing fresh air into your home. A certified contractor can help 

you get all the energy savings and comfort possible from a well sealed 

home, along with the safety of proper ventilation.

1 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Your house is a system and every component in it works together. 

Adding insulation and sealing air leaks can improve the energy 

efficiency of your home and improve your home’s comfort and 

durability. However, every change you make to the building’s 

envelope (walls, floors, and ceiling) and components will affect how 

the home works to keep out the elements and keep your family 

safe and comfortable. Tightening the building envelope without 

providing appropriate ventilation can cause pressure imbalances 

or negative pressure in the house. This negative pressure can set 

up the conditions for backdrafting of fireplaces or fuel-burning 

(combustion) appliances and may draw pollutants into the home. 

A trained contractor understands how systems work together to 

keep your house operating as it should.

This guide gives homeowners tips on where to find a good 

contractor, how to get your home tested for airtightness, where the 

biggest air leaks usually are and how to fix them, what the potential 

health and durability concerns are, and how your contractor can 

handle these concerns—in short, what you need to know to proceed 

with confidence to a more comfortable, energy-efficient, and healthy 

home for your family.

If you are a contractor, share this guide with your customers so that 

they can understand the process you will follow to make their home 

more comfortable, durable, and energy efficient. See the references in 

this guide for detailed explanations of air sealing techniques.

Air Sealing versus Insulation: 

Why do I need to air seal? 

I thought all I needed to do 

was add more insulation.

Insulation is like a fuzzy wool sweater on a 

winter day. It will certainly keep you warm 

if the air is calm. But, if the wind picks 

up, you are going to need a windbreaker 

to keep the breeze from carrying away 

the heat. Air sealing is like adding the 

windbreaker. It keeps the conditioned 

air where it belongs.

Keys to indoor air quality:

•	 Remove pollutant sources, if possible.

•	 Avoid combustion (fuel-burning)

appliances that do not directly vent

to the outdoors. 

•	 Never use non-vented combustion

(e.g., kerosene) heaters inside

the house.

•	 Fix water leaks and moisture

management problems.

•	 Test for radon and carbon

monoxide levels.

•	 Provide adequate ventilation.

April 12, 2010 2

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Finding a Contractor

There are two nationally recognized energy certifications for home 

energy auditors and contractors: the Building Performance Institute 

(BPI) Building Analyst certification and the Residential Energy 

Services Network (RESNET) HERS Rater certification. Historically, 

BPI certification has focused on understanding the building science 

of retrofitting existing homes and RESNET has focused on building 

science in new home construction.

BPI is a nonprofit organization that accredits auditors, contractors, and 

other building professionals. Auditors or building analysts specialize in 

evaluating building systems and potential energy savings in homes. The 

certified BPI Building Analyst energy auditor has passed both written 

and field exams, and must recertify every three years. Contractors learn 

about building systems and are trained to install energy-efficiency 

measures. For more information see www.BPI.org

A certified RESNET energy auditor is called a HERS Rater. HERS 

(the Home Energy Rating System) provides a miles-per-gallon type 

rating for expected energy consumption in homes based on computer 

models. Each home receives a score that can be compared with other 

new or existing homes—the lower the score, the more efficient the home. 

More information about HERS can be found at www.natresnet.org.

An easy way to find a certified contractor is through a national or 

regional retrofit program. One such program is Home Performance 

with ENERGY STAR, a national program from the U.S. 

Environmental Protection Agency and the U.S. Department of 

Energy that promotes a comprehensive, whole-house approach to 

energy-efficiency improvements. To find a Home Performance with 

ENERGY STAR contractor for your area, go to www.energystar.gov

and click on the link for Home Performance with ENERGY STAR. 

Next, click on the “locations” link for certified contractors in 

your state. For cities and states without Home Performance with 

ENERGY STAR contractors, you can find lists of contractors 

in your area who understand the building science whole-house 

approach through the BPI and RESNET websites: www.bpi.org

or www.natresnet.org

Many local, state, and federal entities offer grants and tax credits for 

energy-efficient home improvements. Check with your local utility or 

city, or check the DOE-sponsored Database of State Incentives for 

Renewables and Efficiency (DSIRE) at www.dsireusa.org. This site 

is frequently updated and is a wealth of information, organized by 

state, on state, local, utility, and federal incentives, tax credits, and 

policies that promote renewable energy and energy efficiency.

Certified contractors are trained in 

building science principles to know 

the safest and most effective ways to

improve your home’s energy efficiency.

3 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Test-In/Test-Out

If you are participating in a home performance or weatherization 

program, one of the first steps may be an energy audit. Depending 

on the program, this audit may be conducted by an independent 

auditor or by a weatherization contractor. Details will vary by 

location and program, but here is what you can typically expect. 

Step 1 - The Audit

First, the contractor or auditor should inspect, evaluate, and analyze 

your home. This step is commonly called an audit, but that term has 

been around for a long time and can mean many things. Perhaps the 

most important part of the audit is the conversation between the 

occupants and the auditor. Be prepared to talk about comfort issues 

and energy bills. 

Here is what your audit should include:

•	 Sizing things up – The auditor may measure your house and 

identify square footage, window area, door area, and the condition 

of insulation, mechanical equipment, and air leaks.

•	 Testing in – The auditor will use diagnostic equipment 

to measure how your house performs in ways that cannot be 

seen by eyes alone. These tests may include a blower door test, 

duct pressurization testing, infrared cameras and smoke sticks, 

combustion safety testing, and carbon monoxide sampling. 

A heating and cooling contractor may evaluate your furnace 

and air conditioning system supply and return air balance. 

More information on these tests is included in the next section.

•	 Cost-benefit analysis and estimateS – The auditor 

will estimate the costs of installing the measures and use a computer 

program to estimate the expected energy savings. The cost of the 

measures divided by the annual savings will tell you the “simple pay 

back” or how many years the measures will take to pay for themselves. 

Often investments in energy efficiency provide a better return than 

stocks, bonds, or savings accounts, while improving comfort.

•	 Getting the green light – Expert visual inspections 

and tests can identify safety and operational problems that may 

require attention before any other work on the house proceeds. 

Combustion safety issues must be addressed before air sealing 

begins. Auditors should also point out any obvious sources of 

indoor air pollution. Dry rot and moisture problems must 

be repaired.

Your contractor may test duct leakage as 

part of the home’s energy audit.

Test-In/Test-Out Steps

1 Audit

2 Installing Air Sealing Measures

3 Testing Out

Do not proceed 

with retrofit work if

• The house has active knob and 

tube wiring - Rewire the house first.

• The house has vermiculite insulation -

Vermiculite insulation may contain asbestos. 

Contact your state department of health.

• Bathroom fans are vented into the attic -

Vent fans to outside.

• The house has a leaking roof - Repair the

roof leak before air sealing and insulating.

	 (Lstiburek 2010)

April 12, 2010 4

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Step 2. Installing Air Sealing Measures

Within a week or so, your home performance contractor should 

analyze the test results and provide you with a detailed proposal 

including a prioritized list of energy-efficiency measures, packaged 

options, and cost estimates. Critical safety or health issues should 

be dealt with before work proceeds on the agreed-upon energyefficiency improvements. Your contractor understands state and 

local building codes and will work with code officials when necessary 

to ensure that the improvements meet building code requirements. 

Your contractor may bring in specialized subcontractors if needed. 

Step 3. Testing Out

Testing out means repeating some of the tests used at the beginning 

of the audit process now that the installation is complete. Final 

testing verifies that renovations have improved the home’s 

performance and that safety standards have been met. Some 

contractors offer a guaranteed level of energy savings on their 

retrofit projects. Homeowners receive a report summarizing the 

improvements completed, test results, and estimated energy savings. 

In addition to testing out, in Home Performance with ENERGY 

STAR, at least 1 in 20 homes is spot-checked by independent thirdparty building professionals to ensure program compliance. 

(left) Auditors will check for dry rot and 

moisture problems as well as air leakage.

(middle) Your contractor will visually

inspect the home and test for safety 

concerns before air sealing begins.

(right) Once safety and health issues

have been addressed, your contractor

will proceed with air sealing measures.

Auditors use forms like this one from Energy 

Trust of Oregon for test-in and test-out.

5 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Diagnostic Tools for Test-In and Test-Out

A trained contractor may run these and other diagnostic tests on 

your home as part of the test-in and test-out process. 

Combustion Safety

High-efficiency combustion appliances are usually sealed combustion, 

meaning that they draw in oxygen from outside the home through a 

dedicated vent and send exhaust fumes outside through a separate, 

dedicated vent pipe. These exhaust flues are sealed to prevent backdrafting, where exhaust fumes come back down the flue into the living space. 

Older and less efficient combustion appliances are sometimes 

atmospheric vented, meaning they draw combustion air from the 

room in which they are located, often through an opening at the base 

of the exhaust pipe. Auditors or contractors will check combustion 

appliances such as stoves, furnaces, water heaters, and fireplaces for 

carbon monoxide levels, backdrafting, and other safety hazards, such 

as gas leaks and cracked heat exchangers. If problems are identified, 

no air sealing occurs until the problem is fixed. These may be serious 

safety problems; in rare instances, occupants may need to leave the 

house until problems are repaired.

Blower Door

A blower door uses a calibrated fan to measure how much air a 

home leaks. The blower door mounts into an exterior door frame. 

The fan pulls air out of the house, lowering the air pressure inside. 

Outside air then flows into the house through all unsealed cracks 

and openings. The amount of fan pressure required by the fan to 

maintain the test pressure tells the auditor how much leakage the 

house has. Some contractors will seal simple air leaks as they 

are identified while the blower door is operating.

Infrared Camera

An infrared camera produces images called thermographs that show 

variations in temperature not visible to the human eye. Infrared 

cameras can be used during blower door tests to capture images 

of temperature differences that can indicate air leakage or other 

conditions such as gaps in insulation and overheating circuits. 

Duct Blaster

Leaky ducts in attics or crawlspaces can account for 20% or more 

of a home’s heating and cooling energy losses. A Duct Blaster (duct 

pressurization test) uses a calibrated fan to test the air leakage rate 

in air ducts. Another approach uses a blower door and a shallow 

pan (a pressure pan) to cover each register and grill to measure and 

prioritize duct leaks.

(top) Your contractor can use a blower 

door to measure overall house air leakage.

(bottom) The infrared cameras can show

air leaks not visible to the naked eye.

If initial testing or inspections 

identify any health or safety 

problems, no air sealing occurs 

until the problem is fixed.

April 12, 2010 6

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Safety and Health Issues 

Inspection and testing can identify health and safety issues 

that should be fixed before any air sealing or other efficiency 

improvements are made. Taking care of these issues is important to 

your family’s health, and these issues should be fixed before doing 

any home improvements. If the problems are severe, fix them before 

returning home. Here are some problems to watch for. 

•	 Backdrafting – Air pressure imbalances between the outside 

and inside or between rooms of the house can cause fireplaces, 

furnaces, and other appliances that burn fuel (such as wood and 

natural gas) to pull exhaust gases back into the house instead 

of letting them vent up the flue. This situation is known as 

backdrafting. Carbon monoxide (CO), a toxic gas without odor 

and color, can backdraft into homes causing illness and death. 

•	 Roll-Out – Combustion appliances may have a pilot light flame. 

Backdrafting, air pressure imbalances, and mechanical problems 

can cause the pilot to blow out, or worse, the flame can “roll out” 

of the appliance, causing a house fire.

•	 Moisture Problems – If the home is not properly ventilated, 

water vapor from showering, cooking, breathing, and burning fuels 

can concentrate in the home increasing humidity levels. This can 

lead to mold and mildew, dust mites, wood rot, material damage, 

and subsequent health and structural problems.

•	 AIR POLLUTANTS – Many homes contain hazardous substances 

(such as cigarette smoke, volatile organic compounds and other 

offgases from carpets, paints, finishes, and home electronics; 

cleaning chemicals; and pesticides) as well as allergens (such as 

pet dander and dust mites). It is important to avoid or exhaust 

pollutants at their source. Also, air pressure imbalances between 

the outside and inside of the house can draw in pollutants from 

outside. These can include solvents and car exhausts from attached 

garages or radon emanating from the soil.

•	 RadoN – Radon is a naturally occurring radioactive gas. Radon 

gas is colorless, odorless, and tasteless and cannot be detected by 

human senses. In some geographic areas with high concentrations 

of radon in the soil, it can accumulate in the home and may 

adversely affect human health.

(top) Studies show homes and garages 

may contain over 150 household products

that may be harmful to humans.

(bottom) Lack of ventilation, poor moisture

management, installation issues, and 

pressure imbalances combine leading to 

mold problems inside walls.

Be Safe:

All combustion appliances should be 

tested for backdrafting. Replace natural

draft combustion appliances with 

sealed combustion, induced draft, or 

power-vented appliances, if possible.

Homes with combustion appliances 

should have carbon monoxide

detectors that meet UL 2034.

7 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Ventilate it Right

Studies show the average American spends up to 90% of their time 

indoors. About 23 million people including 6.8 million children in the 

United States now suffer from asthma. Some see a correlation and 

point to indoor air pollutants—chemicals, gases, mold, dust, etc.—

as a culprit. To provide fresh air in your older home, your contractor 

may recommend adding mechanical ventilation.

An old adage for building scientists is “build tight, ventilate right.” 

When air leaks in the home are sealed up, mechanical ventilation 

may need to be added. 

There are several options for mechanical ventilation systems. Spot 

ventilation, using exhaust-only fans in the kitchen and bathroom, 

removes water vapor and pollutants from specific locations in the 

home, but does not distribute fresh air. Balanced ventilation systems, 

like air-to-air exchangers, heat-recovery ventilators, and energyrecovery ventilators, both supply and exhaust air. Your contractor 

can help you determine which one is most appropriate for your 

specific climate, house design, and budget.

Pros and Cons of Various Mechanical Ventilation Systems

Ventilation Type Pros Cons

Exhaust Only

(air is exhausted

from the house 

with a fan)

•	 Easy to install

•	 Simple method for 

spot ventilation

•	 Inexpensive

• Negative pressure may

cause backdrafting

• Makeup air is from 

random sources

• Removes heated or

cooled air

Supply Only

(air is supplied into

the house with a fan)

•	 Does not interfere with 

combustion appliances

•	 Positive pressures inhibit

pollutants from entering

•	 Delivers to

important locations

• Does not remove indoor

air pollutants at their 

source

• Brings in hot or cold air 

or moisture from outside

• Air circulation can 

feel drafty

• Furnace fan runs more

often unless fan has an 

ECM (variable-speed motor)

Balanced 

Air Exchange 

System

(heat and energy

recovery ventilators)

•	 No combustion impact

•	 No induced

infiltration/exfiltration

•	 Can be regulated to 

optimize performance

•	 Provides equal supply

and exhaust air

•	 Recovers up to 80% of the

energy in air exchanged

• More complicated design 

considerations

• Over ventilation unless

the building is tight

• Cost

Heat and Energy Recovery 

Ventilation Systems

Heat-recovery ventilators (HRVs) and

energy-recovery (or enthalpy-recovery)

ventilators (ERVs) both provide a

controlled way of ventilating a home

while minimizing energy loss by using 

conditioned exhaust air to warm or cool

fresh incoming air. There are some small

wall- or window-mounted models, but

the majority are central, whole-house

ventilation systems that share the furnace

duct system or have their own duct system.

The main difference between an HRV and

an ERV is the way the heat exchanger

works. With an ERV, the heat exchanger

transfers water vapor along with heat

energy, while an HRV only transfers heat.

The ERV helps keep indoor humidity

more constant. However, in very humid

conditions, the ERV should be turned off

when the air conditioner is not running. 

Air-to-air heat exchangers or heat recovery

ventilators (HRV’s) are recommended

for cold climates and dry climates. 

Energy recovery ventilators (ERV’s) are

recommended for humid climates.

Most energy recovery ventilation systems

can recover about 70%–80% of the energy

in the exiting air. They are most cost

effective in climates with extreme winters

or summers, and where fuel costs are 

high. Energy recovery ventilation systems

operated in cold climates must have

devices to help prevent freezing and

frost formation.

Ventilation – too little, 

too much, just right 

Too little ventilation can lead to indoor

air quality problems, too much can waste

energy and cause comfort issues. Your 

contractor will use ASHRAE Standard 62.2

and other industry guidelines to determine 

how much passive and mechanical

ventilation is right for your home.

April 12, 2010 8

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
New Code Air Sealing Requirements 

The 2009 International Energy Conservation Code (IECC) and 

the 2009 International Residential Code (IRC) have several new 

mandatory requirements for air sealing in new construction and 

additions. These codes apply to new construction where adopted by 

local jurisdictions. In general, these requirements do not apply to 

retrofit projects unless the project adds living space to the building 

or changes the building’s energy load. The existing, unaltered 

portions of the structure are not required to comply with all of the 

requirements of the 2009 IECC or IRC. However, Building America 

recommends implementing these requirements in existing portions 

of your home wherever they are applicable and your budget allows 

or health and safety concerns make them necessary.

The requirements regarding new buildings can be summarized in 

this section excerpted from IECC, Chapter 4, Section 402.4, Air 

Leakage (mandatory) (quoted verbatim). Builders can see IECC 

2009, Chapter 4 “Residential,” and IRC 2009, Chapter 11 “Energy 

Efficiency,” for more details:

“The building thermal envelope shall be durably sealed to 

limit infiltration. The sealing methods between dissimilar materials 

shall allow for differential expansion and contraction. The following 

shall be caulked, gasketed, weather stripped or otherwise sealed 

with an air barrier material, suitable film, or solid material: 

1. all joints, seams and penetrations,

2. site-built windows, doors, and skylights,

3. openings between window and door assemblies and their 

respective jambs and framing, 

4. utility penetrations, 

5. dropped ceilings or chases adjacent to the thermal envelope,

6. knee walls, 

7. walls and ceilings separating a garage from conditioned spaces, 

8. behind tubs and showers on exterior walls, 

9. common walls between dwelling units, 

10. attic access openings, 

11. rim joists junction, 

12. other sources of infiltration.”

The holes in the sill plate were properly air

sealed during construction of this house.

9 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
An Air Sealing Checklist

This section provides descriptions of the areas of the home most 

likely to have air leakage, when to address those problems, durability 

and health concerns related to the problems, and references for more 

information. Additional information on how to identify and fix 

these problems and other building science information can be found 

in the Building America Best Practices guides produced by DOE 

and available for free download at www.buildingamerica.gov. Work 

with your contractor to determine which of these measures are most 

needed and most cost-effective. 

Common air sealing trouble spots are shown on the graphic below 

and listed on the following page. Each of these trouble spots is 

described further in the pages that follow.

Get the Details

Contractors, see the references in the 

sections below for detailed descriptions 

of air sealing techniques and technologies.

Building America research identifies 19 key areas where air sealing can improve a

home’s energy efficiency, comfort, and building durability. The information in this

guide can help you find a certified home performance contractor and work with 

your contractor to identify problem areas, prioritize projects with safety in mind, 

and start sealing the air leaks in your home for cost-effective energy savings.

Air Sealing Trouble Spots

1. Air Barrier and Thermal 

Barrier Alignment

2. Attic Air Sealing

3. Attic Kneewalls

4. Shaft for Piping or Ducts

5. Dropped Ceiling/Soffit

6. Staircase Framing at Exterior Wall 

7. Porch Roof 

8. Flue or Chimney Shaft

9. Attic Access

10. Recessed Lighting

11. Ducts

12. Whole-House Fan

13. Exterior Wall Penetrations 

14. Fireplace Wall

15. Garage/Living Space Walls

16. Cantilevered Floor

17. Rim Joists, Sill Plate, Foundation, Floor

18. Windows & Doors 

19. Common Walls Between 

Attached Dwelling Units

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

18 15 19

3

13

18

16

17

5 4

14

9

13

6

1

8

17

17

10

12

13 7

11

2

April 12, 2010 10

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RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Air Sealing List 

Each of these items is addressed on the following pages.

Air Barrier Completion Guidelines

1. Air Barrier and Thermal Barrier Alignment Air barrier is in alignment with the thermal barrier (insulation).

2. Attic Air Sealing Top plates and wall-to-ceiling connections are sealed.

3. Attic Kneewalls Air barrier is installed at the insulated boundary 

(kneewall transition or roof, as appropriate).

4. Duct Shaft/Piping Shaft and Penetrations Openings from attic to conditioned space are sealed.

5. Dropped Ceiling/Soffit Air barrier is fully aligned with insulation; all gaps are fully sealed.

6. Staircase Framing at Exterior Wall/Attic Air barrier is fully aligned with insulation; all gaps are fully sealed.

7. Porch Roof Air barrier is installed at the intersection of the porch roof 

and exterior wall.

8. Flue or Chimney Shaft Opening around flue is closed with flashing, and any remaining

gaps are sealed with fire-rated caulk or sealant.

9. Attic Access/Pull-Down Stair Attic access panel or drop-down stair is fully gasketed for

an air-tight fit.

10. Recessed Lighting Fixtures are provided with air-tight assembly or covering.

11. Ducts All ducts should be sealed, especially in attics, vented crawlspaces,

and rim areas.

12. Whole-House Fan Penetration at Attic An insulated cover is provided that is gasketed or sealed to the

opening from either the attic side or ceiling side of the fan.

13. Exterior Walls Service penetrations are sealed and air sealing is in place behind

or around shower/tub enclosures, electrical boxes, switches, and

outlets on exterior walls.

14. Fireplace Wall Air sealing is completed in framed shaft behind the fireplace or at 

fireplace surround.

15. Garage/Living Space Walls Air sealing is completed between garage and living space.

Pass-through door is weather stripped.

16. Cantilevered Floor Cantilevered floors are air sealed and insulated at perimeter

or joist transition.

17. Rim Joists, Sill Plate,

Foundation, and Floor

Rim joists are insulated and include an air barrier. Junction of

foundation and sill plate is sealed. Penetrations through the bottom

plate are sealed. All leaks at foundations, floor joists, and floor

penetrations are sealed. Exposed earth in crawlspace is covered with

Class I vapor retarder overlapped and taped at seams.

18. Windows and Doors Space between window/door jambs and framing is sealed.

19. Common Walls Between

 Attached Dwelling Units

The gap between a gypsum shaft wall (i.e., common wall) and the

structural framing between units is sealed.

11 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
1. Air Barrier and 

Thermal Barrier Alignment 

The air barrier is in alignment with (touching) the 

thermal barrier (insulation).

Convective loops can form in wall cavities if there are gaps between 

the insulation and the air barrier. Convective loops (air movement 

within the wall cavities caused by temperature differences) will 

get cold air falling and hot air rising. This air movement reduces 

the effectiveness of the insulation and can pull in outside air and 

cause moisture problems. Arches, soffits, chases, and other design 

features create an uneven air barrier (drywall plane) that is difficult 

to insulate thoroughly. Expect the contractor to inspect these areas 

visually or with an infrared camera to make sure batts or blown 

insulation completely fill wall cavities.

Thermal and air barrier alignment is not an issue with insulation 

materials like spray foam or rigid foam that form an air barrier as 

well as thermal barrier, as long as they form a continuous air barrier 

from top to bottom and side to side. Spray foams should be sprayed 

to a consistent minimum depth across the area to be sealed and 

insulated. Rigid foam board that is serving as the air and thermal 

barrier should be taped at the seams with housewrap tape and glued 

with caulk at the edges to the wall framing, sill plate, or top plate. 

Blown cellulose and blown or batt fiberglass insulation will not 

stop air flow. 

Figure 1.1. (left) Cut fiberglass batt insulation to fit around electrical boxes and

wiring or pipes that run through the walls. Compressions like these ruin the batt’s

thermal alignment with walls and lessen its effectiveness.

Figure 1.2. (right) Install batts to fit smoothly and to completely fill wall and ceiling 

cavities. Here fiberglass batts completely fill joists of basement ceiling.

When To Do This

When replacing dry wall, replacing siding, 

adding an addition, adding insulation to 

attic or crawlspace or any time access 

is available.

Durability & Health

Convective loops in walls can pull in

pollen, dust, and moisture. Walls that 

are not well insulated can provide a cold

surface in wall cavities where warm indoor

air can condense in winter and warm 

outdoor air can condense in the summer, 

encouraging mold growth in walls.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Air barrier and thermal barrier

•	 Exterior thermal envelope insulation for

framed walls is installed in substantial 

contact and continuous alignment with 

building envelope air barrier.

•	 Breaks or joints in the air barrier are

filled or repaired.

•	 Air-permeable insulation is not used

as a sealing material.

•	 Air-permeable insulation is inside

of an air barrier.

More Information 

•	 Building America Best Practices

•	 U.S. Department of Energy 2009b

•	 U.S. Environmental Protection

Agency 2008b

April 12, 2010 12

12

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Caulk where drywall 

meets top plate

Ceiling drywall taped 

or caulked to wall drywall

2. Attic Air Sealing 

Top plates and wall-to-ceiling connections are sealed.

Good air-sealing and a continuous air barrier between the attic and 

the home’s conditioned (living) space are important not only to save 

energy and reduce fuel bills, but also to prevent moisture problems 

in the attic. Sealing holes in the attic makes chimneys and flues 

work better because a leaky attic ceiling acts like a chimney and will 

compete with the real chimney for air. Air sealing the leaky attic 

ceiling also reduces the house’s “suction” (or stack effect) so less 

contaminants are drawn up into the house from the ground such 

as radon and other soil gases (Lstiburek 2010). 

On the inside of the home, the ceiling drywall can serve as an air 

barrier. Visible cracks at the seam of the wall and ceiling can be 

taped, mudded, and painted or filled with paintable caulk, such as 

silicon latex. Your contractor can determine where leaks are with 

an infrared camera, by feeling for air flow, or by inspecting the 

attic insulation. Dirty insulation is an indication that air is flowing 

through the insulation and pulling dust with it.

Your contractor may pull back or scoop out the insulation to apply 

caulk, spray foam, or other sealant where the walls meet the attic 

floor. Other places in the attic that often are big sources of air leaks 

are soffits (dropped-ceiling areas, duct chases, plumbing chase), 

behind or under attic kneewalls, around recessed can lights, around 

flue pipes, around ducts, and at attic hatches (see strategy #3, #4, 

#5, #8, #9, #10, and #11). 

When To Do This

When replacing dry wall, replacing siding, 

adding an addition, adding insulation to 

attic, anytime you see cracks at the inside 

seam of the wall and ceiling. In vaulted 

ceilings, the ceiling-to-wall intersection can 

be accessed and sealed from the inside or 

from the outside when reroofing occurs.

Durability & Health

Heat moves from high-temperature regions 

to low-temperature regions. The warmer 

the air, the more water vapor it can carry 

with it. If warm, moist air gets into a cold 

attic through leaks in the home’s thermal 

envelope, it can condense on rafters and 

other solid surfaces, which may lead to 

water damage and mold growth.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Ceiling/attic

Air barrier in any dropped ceiling/soffit is 

substantially aligned with insulation and 

any gaps are sealed.

More Information 

•	 Building America Best Practices

•	 Lstiburek 2010

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2008c

Spray foam

top plate 

to air seal

Figure 2.2. Pull back insulation to seal

drywall to top plate with spray foam, caulk, 

or other sealer (Lstiburek 2010).

Figure 2.1. Seal the wall drywall to

the top plate and ceiling drywall. 

EXTERIOR TOP PLATE AT SOFFIT 

TASK – Control air leakage at top plate, provide insulati

1.

2.

3.

Alternate Method

2a.

13 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
3. Attic Kneewalls

Air barrier is installed at the insulated boundary 

(kneewall transition or roof, as appropriate).

Kneewalls, the sidewalls of finished rooms in attics, are often leaky 

and uninsulated. Your contractor can insulate and air seal these 

walls in one step by covering them from the attic side with sealed 

rigid foam insulation. Your contractor can plug the open cavities 

between joists beneath the kneewall with plastic bags filled with 

insulation or with pieces of rigid foam. Another option is to apply 

rigid foam to the underside of the rafters along the sloped roof line 

and air seal at the top of the kneewall and the top of the sidewall, 

which provides the benefit of both insulating the kneewall and 

providing insulated attic storage space. 

Doors cut into kneewalls should also be insulated and airsealed by 

attaching rigid foam to the attic side of the door, and using a latch 

that pulls the door tightly to a weather-stripped frame. 

When To Do This

Any time you have access to kneewalls.

Durability & Health

If warm moist air gets into a cold attic 

through leaks in the home’s thermal

envelope, it can condense on rafters and

other solid surfaces, which may lead to 

water damage and mold growth.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Ceiling/attic

Attic access (except unvented attic),

kneewall door, or drop down stair 

is sealed.

More Information 

•	 Building America Best Practices

•	 Iowa Energy Center 2008

•	 Lstiburek 2010

•	 U.S. Department of Energy 2000a

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2008b

•	 U.S. Environmental Protection

Agency 2008c

Seal

Attic living

space Hardboard

Desired

ventilation

Option 1 Option 2

Seal air barrier at edges

Seal

Insulated Box

Drawers

Drawers

Figure 3.1. Insulate and air

seal the kneewall itself, as 

shown, or along the roof line 

(Source: DOE 2000a).

Figure 3.2. Air seal floor joist

cavities under kneewalls by

filling cavities with fiberglass

batts that are rolled and stuffed 

in plastic bags (as shown here)

or use rigid foam, OSB, or other

air barrier board cut to fit and 

sealed at edges with caulk.

Figure 3.3. Build an airtight,

insulated box around any

drawers or closets built into 

attic knee walls that extend into

uninsulated attic space. Insulate 

along air barrier (shown in

yellow on drawing) or along roof

line with rigid foam (Source:

Iowa Energy Center 2008).

April 12, 2010 14

14

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
4. Duct Shaft/Piping Shaft 

and Penetrations

Openings from attic to conditioned space are sealed.

Any chases, shafts, or building cavities that contain piping or wiring 

can serve as links between conditioned and unconditioned space. 

Your contractor can inspect these areas and close the gaps with caulk, 

spray foam, and blocking material (pieces of rigid foam, plywood, or 

oriented strand board cut to fit and sealed in place with spray foam). 

Furnace flues require high-temperature-rated sealing materials.

Figure 4.1. Seal attic and wall penetrations associated with

mechanical ventilation systems, electrical chase openings, and dropped

soffits (Source: DOE 2000a).

When To Do This

Any time you have access.

Durability & Health

HVAC, plumbing, and wiring chases can 

bring conditioned air into attics, leading 

to condensation and mold problems. They

can also connect crawlspaces and living

spaces bringing soil gases into the home.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Shafts, penetrations

Duct shafts, utility penetrations, knee 

walls and flue shafts opening to exterior

or unconditioned space are sealed.

More Information 

•	 Building America Best Practices

•	 Iowa Energy Center 2008

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2008c

•	 House Energy 2009

Seal with

sheet metal Seal and insulate 

and high-temp dropped soffit 

caulk Seal

chases

Caulk

electrical 

fixtures to 

drywall Seal HVAC 

penetrations 

Seal electrical 

penetrations 

Seal

bottom Seal plumbing 

penetrations plate

15 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
5. Dropped Ceiling/Soffit

Air barrier is fully aligned with insulation; 

all gaps are fully sealed.

Soffits (dropped ceilings) found over kitchen cabinets or sometimes 

running along hallways or room ceilings as duct or piping chases 

are often culprits for air leakage. Your contractor will push aside 

the attic insulation to see if an air barrier is in place over the 

dropped area. If none exists, the contractor will cover the area 

with a piece of rigid foam board, sheet goods, or reflective foil 

insulation that is glued in place and sealed along all edges with 

caulk or spray foam, then covered with attic insulation. If the 

soffit is on an exterior wall, sheet goods or rigid foam board 

should be sealed along the exterior wall as well. If the soffit 

contains recessed can lights, they should be rated for insulation 

contact and airtight (ICAT) or a dam should be built around 

them to prevent insulation contact.

Figure 5.1. Place a solid air barrier over soffits as follows: pull back existing

insulation; cover area with air barrier material (gypsum, plywood, OSB, rigid

foam, etc.); seal edges with caulk; cover with insulation (Lstiburek 2010).

When To Do This

Any time, if attic construction allows 

access to area above soffits.

Durability & Health

If warm moist air gets into a cold attic 

through leaks in the home’s thermal

envelope, it can condense on solid

surfaces, which may lead to water 

damage and mold growth.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Ceiling/attic

Air barrier in any dropped ceiling/soffit

is substantially aligned with insulation 

and any gaps are sealed.

More Information 

•	 Building America Best Practices

•	 Iowa Energy Center 2008

•	 Lstiburek 2010

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2008b

•	 U.S. Environmental Protection

Agency 2008c

DROPPED SOFFITS (Bulkheads, Arches) Guide to Attic Air Se

Terminology

Air Barrier Material (ABM) --- Any rigid or semi r

does not allow air to pass through it. Examples: 

plywood/OSB, foam board, duct board, sheet m

lumber.

Backing --- Any material that serves as a surfac

TASK – Control air leakage between the conditioned space below and the unconditioned attic space ab

dropped soffits.

Steps 

• Expose the dropped soffit includ

[1].

• Measure and pre cut the ABM to 

the drop or opening in the ceiling.

• Fix in place the ABM using adhes

• Air seal all edges of ABM to frami

[2].

Detail ready for insulation [3,4] 1.

2.

3.

Sealant on gypsum and top plate

3/4” closure board (OSB, plywood,

gypsum board, rigid insulation)

Continuous bead of adhesive

around perimeter of closure board

April 12, 2010 16

16

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
6. Staircase Framing at 

Exterior Wall/Attic

Air barrier is fully aligned with insulation; 

all gaps are fully sealed.

If the area under the stairs is accessible, look to see if the inside wall 

is finished. If not, have your contractor insulate it, if needed, and 

cover it with a solid sheet product like drywall, plywood, oriented 

strand board, or rigid foam insulation. Then, your contractor can 

caulk the edges and tape the seams to form an air-tight barrier. 

Stairs should be caulked where they meet the wall.

Figure 6.1. Install an air barrier and air sealing on exterior walls behind stairs.

If the area behind the stairs is inaccessible, caulk stairs where they meet the wall. 

Use caulk if the area is already painted; use tape and joint compound if area 

will be painted.

When To Do This

Any time.

Durability & Health

Uninsulated exterior walls with no air

barriers present a cold surface where 

condensation and mold can form.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Air barrier and thermal barrier

•	 Exterior thermal envelope insulation for

framed walls is installed in substantial 

contact and continuous alignment with 

building envelope air barrier.

•	 Air-permeable insulation is inside of

an air barrier.

More Information 

•	 Building America Best Practices

•	 U.S. Environmental Protection

Agency 2008c

•	 House Energy 2009

Gypsum

board

Structural

sheathing

Tape and joint

compound seal

17 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
7. Porch Roof

Air barrier is installed at the intersection of the porch 

roof and exterior wall.

If a test-in inspection identifies air leakage at the wall separating 

the porch from the living space, the contractor will investigate to 

see if the wall board is missing or unsealed. If this is the case, the 

contractor will install some type of wall sheathing (oriented strand 

board, plywood, rigid foam board) cut to fit and sealed at the edges 

with spray foam. Your contractor will also make sure this wall 

separating the attic from the porch is fully insulated.

When To Do This

Any time, if porch wall is accessible, 

either from the attic or from the porch.

Durability & Health

Cold surfaces in the exterior wall

encourage condensation and mold. If the 

air barrier is missing, wind can carry dust 

and pollen into the living space.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Air barrier and thermal barrier

•	 Exterior thermal envelope insulation for

framed walls is installed in substantial 

contact and continuous alignment with 

building envelope air barrier.

•	 Breaks or joints in the air barrier are

filled or repaired.

•	 Air-permeable insulation is inside of

an air barrier.

More Information 

•	 Building America Best Practices

•	 Moriarta 2008

•	 U.S. Environmental Protection

Agency 2008b

Studies Show

Steven Winter Associates, a Building America research team lead, used

a blower door test and infrared cameras to investigate high-energy bill

complaints at a 360-unit affordable housing development and found nearly

twice the expected air leakage. Infrared scanning revealed an air leakage

path on an exterior second-story wall above a front porch. Steven Winter

Associates found that, while the wall between the porch and the attic had 

been insulated with unfaced fiberglass batts, wall board had never been

installed. The insulation was dirty from years of windwashing as wind

carried dust up through the perforated porch ceiling, through the insulation, 

into the attic and into the wall above. Crews used rigid foam cut to fit and

glued in place with expandable spray foam to seal each area. Blower door

tests showed the change reduced overall envelope leakage by 200 CFM50. 

At a cost of $267 per unit, this fix resulted in savings of $200 per year per

unit, for a payback of less than two years.

Figure 7.1. When researchers pulled back the porch ceiling, they found

the wall board was missing so nothing was covering the insulation on this

exterior wall. An air barrier of rigid foam board was put in place with spray

foam (Source: Moriarta 2008).

April 12, 2010 18

18

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
8. Flue or Chimney Shaft

Opening around flue is closed with flashing, and any 

remaining gaps are sealed with fire-rated caulk or sealant.

There are often gaps around chimneys, furnaces, and water heater 

flues that allow conditioned air to flow up into the attic. Your 

contractor can seal this gap with lightweight aluminum flashing 

(sheet metal) and special high-temperature (heat-resistant) caulk. A 

metal dam should be used to 

keep insulation away from the 

flue. The same technique is 

used for masonry chimneys. 

 

Figure 8.1.

Step 1: Cut aluminum flashing

to fit around flue.

Figure 8.2.

Step 2: Seal flashing to pipe with

high-temperature caulk.

Figure 8.3.

Step 3: Form an insulation dam to

keep the insulation from coming 

into contact with the flue pipe.

When To Do This

Any time the flue pipe is accessible

in the attic.

Durability & Health

Use the right sealing products and 

techniques to keep flammable materials

from touching hot flues.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Shafts, penetrations

Duct shafts, utility penetrations, knee 

walls and flue shafts opening to exterior

or unconditioned space are sealed.

More Information 

•	 Building America Best Practices

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2008c

SEALING ATTIC AIR LEAKS 

Furnace Flues Require Special Sealing Techniques 

The opening around a furnace or water heater flue or chimney can be a major source of 

warm air moving in the attic. Because the pipe gets hot, building codes usually require 

1 inch of clearance from metal flues (2 inches from masonry chimneys) to any combustible 

material, including insulation. Photos 5 and 6 show how to seal this gap with lightweight 

aluminum flashing and special high-temperature (heat-resistant) caulk. Before you push 

the insulation back into place, build a metal dam (photo 7) to keep it away from the pipe. 

Use the same technique for masonry chimneys. 

5. CUT ALUMINUM FLASHING 

14” ALUMINUM 

FLASHING 

OPEN JOIST 

CAVITY 

HIGH-TEMP 

CAULK 

CLASS B 

FURNACE FLUE 

Caution: Furnace flues (the 

pipe that removes your furnace 

exhaust) can be very hot. 

Cut aluminum flashing to fit around the flue. For 

round flues, cut half circles out of two pieces so 

they overlap about 3 inches in the middle. Press 

the flashing metal into a bead of high-temperature 

caulk and staple or nail it into place. If there’s no 

wood, staple or nail it directly to the drywall, but 

be sure not to staple or nail through the drywall. 

6. SEAL WITH SILICONE CAULK 

HIGH-TEMP 

CAULK 

Seal the gap between the flue and metal flas

with special high-temperature caulk. Don’t u

spray foam. 

Identifying Attic Pipes 

FLUES/VENTS/PIPES: MAD

Furnace/Water Heater Gala

Chimney Mas

Plumbing Cast 

1.8 SEALING ATTIC AIR LEAKS 

AKS 

al Sealing Techniques 

heater flue or chimney can be a major source of 

e pipe gets hot, building codes usually require 

ches from masonry chimneys) to any combustible 

nd 6 show how to seal this gap with lightweight 

perature (heat-resistant) caulk. Before you push 

etal dam (photo 7) to keep it away from the pipe. 

mneys. 

5. CUT ALUMINUM FLASHING 

14” ALUMINUM 

FLASHING 

OPEN JOIST 

CAVITY 

HIGH-TEMP 

CAULK 

CLASS B 

FURNACE FLUE 

Cut aluminum flashing to fit around the flue. For 

round flues, cut half circles out of two pieces so 

they overlap about 3 inches in the middle. Press 

the flashing metal into a bead of high-temperature 

caulk and staple or nail it into place. If there’s no 

wood, staple or nail it directly to the drywall, but 

6. SEAL WITH SILICONE CAULK 

HIGH-TEMP 

CAULK 

Seal the gap between the flue and metal flashing 

with special high-temperature caulk. Don’t use 

spray foam. 

Identifying Attic Pipes 

7. FORM AN INSULATION DAM 

INSULATION DAM 

1” TABS 

RENT IN 

STAPLE 

DOWN 

2” TABS 

BENT OUT 

Form an insulation dam to prevent insulation from 

contacting the flue pipe. Cut enough aluminum from 

the coil to wrap around the flue plus 6 inches. Cut 

slots 1 inch deep and a few inches apart along the 

top and bend the tabs in. Cut slots about 2 inches 

deep along the bottom and bend out the tabs. Wrap 

the dam around the flue and secure the bottom by 

stapling through the tabs. Now put insulation back 

right up against the dam. 

FLUES/VENTS/PIPES: MADE OUT OF: SEAL AROUND WITH: 

Furnace/Water Heater Galanized Metal Aluminum flashing and hightemperature silicone caulk 

Aluminum flashing and high- Chimney Masonry/Metal 

le 

6. SEAL WITH SILICONE CAULK 

HIGH-TEMP 

CAULK 

Seal the gap between the flue and metal flashing 

with special high-temperature caulk. Don’t use 

spray foam. 

7. FORM AN INSULATION DAM 

INSULATION DAM 

1” TABS 

RENT IN 

STAPLE 

DOWN 

2” TABS 

BENT OUT 

Form an insulation dam to prevent insulation from 

contacting the flue pipe. Cut enough aluminum from 

the coil to wrap around the flue plus 6 inches. Cut 

slots 1 inch deep and a few inches apart along the 

top and bend the tabs in. Cut slots about 2 inches 

deep along the bottom and bend out the tabs. Wrap 

(Source: EPA 2008a)

19 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Air seal gasket between

trim and panel

Insulation dams prevent loose-fill 

insulation from falling through access

The hatch lid pushes up and

out of the way for access

Weatherstripping

Weatherstripping Seal gap between frame

and rough opening with 

Panel caulk, backer rod, or foam

Insulation dams prevent

loose-fill insulation from

falling through access

The cover box pushes up and

out of the way for access

Air seal gasket between

trim and panel

Insulation dams prevent loose-fill 

insulation from falling through access

The hatch lid pushes up and

out of the way for access

Weatherstripping

Weatherstripping Seal gap between frame

and rough opening with 

Panel caulk, backer rod, or foam

Insulation dams prevent

loose-fill insulation from

falling through access

The cover box pushes up and

out of the way for access

9. Attic Access/Pull-Down Stair

Attic access panel or drop-down stair is fully gasketed 

for an air-tight fit.

A home’s attic access, which could be an attic hatch, pull-down 

stairs, or a kneewall door, can leak a lot of heated or cooled air into 

the attic if it is not sealed properly. 

Your contractor can add weather stripping either to the frame or 

panel of the attic access and may install latch bolts to ensure a 

tighter seal. The hatch lid, stairs, or door should be insulated too.

If you are planning to add an attic access, consider the location. An 

access hatch or pull-down stairs that is located in an unconditioned 

part of the house, such as a garage, covered patio, or porch, does 

not necessarily need to be air sealed or insulated. If your hatch 

connects conditioned space like a bedroom, hallway, or closet to an 

unconditioned attic, your contractor will check for air leakage.

Figure 9.1. Insulate and air seal the attic access hatch cover.

Figure 9.2. Insulate and air seal the pull-down attic stair.

When To Do This

Any time.

Durability & Health

Air sealing the attic access will minimize 

the amount of moisture-laden air that

escapes into the attic reducing the risk 

of mold in the attic.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Ceiling/attic

Attic access (except unvented attic), knee

wall door, or drop down stair is sealed.

More Information 

•	 Building America Best Practices

•	 U.S. Department of Energy 2000b

•	 U.S. Department of Energy 2009a

•	 U.S. Environmental Protection

Agency 2008a

April 12, 2010 20

20

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
10. Recessed Lighting

Fixtures are provided with air-tight assembly or covering.

Recessed downlights are the most popular home lighting fixture 

in the United States. Older model recessed can fixtures are energy 

intensive in three ways—they are not approved for insulation 

contact so insulation has to be kept at least 3 inches away all the way 

around, leaving about 1 square foot of uninsulated ceiling space. 

Most are using incandescent bulbs that use 3 to 5 times the power of 

fluorescents and add to air-conditioning loads. Third, the cans are 

not airtight, so they allow conditioned air to escape from the living 

area into unconditioned spaces such as attics. 

If your home has non-airtight fixtures, you can have a contractor 

replace the whole fixture with insulation contact-rated, air-tight 

(ICAT) fixtures, or caulk around the fixture, under the trim ring if 

caulking from inside the home. Other alternatives are to install the 

recessed cans in an air-sealed dropped soffit or to use surface-mounted 

fixtures instead. After air sealing, replace any incandescent lights in 

the recessed lighting fixture with low-wattage CFL or LED lamps.

When To Do This

Replace old uninsulated can fixtures

when changing lighting fixtures;

can caulk any time.

Durability & Health

Non-airtight recessed can fixtures

can allow heated air to escape to attic 

during winter, carrying moisture that 

can condense in a cool attic. They can

also draw hot attic air into the home in 

summer, pulling dust and insulation 

particles into the home.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Recessed lighting

Recessed light fixtures are airtight, IC

rated, and sealed to drywall. Exception:

fixtures in conditioned space.

More Information 

•	 Building America Best Practices

•	 ASTM 1991

•	 McCullough and Gordon 2002

Figure 10.1. (left) Replace old, leaky can

fixtures with insulated, airtight recessed

light fixtures and caulk them where the

housing meets the drywall.

Figure 10.2. (right) Seal cans to 

prevent heated and cooled air from

leaking into attics as shown in this 

infrared camera image.

Recessed light fixtures 

should be rated for 

insulation contact and 

air tight (ICAT).

AIR TIGHTNESS 

LABEL

Airtight wire 

connection from 

junction box

Airtight

can

Decorative

cover Caulk

or Gasket

Studies Show

Old, leaky recessed cans are like a hole in the ceiling, only worse. Old

recessed cans with incandescent bulbs can pull 3 to 5 times as much air as

a hole the same size, thanks to the “stack effect”—the heat inside the can

pulls air from the house up into the attic. Replacing a leaky can with an

ICAT (insulation contact-rated, air-tight) recessed downlight would save a

Phoenix, AZ, homeowner $1.56 per year in cooling costs or a Minneapolis,

MN, homeowner $3.57 per year in heating costs (these savings don’t even

include the possible energy savings of CFL bulbs over incandescent bulbs)

(McCullough and Gordon 2002).

21 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
11. Ducts

All ducts should be sealed, especially in attics, vented 

crawlspaces, and rim areas.

Repairing leaking ducts can yield big energy improvements. Duct 

sealing contractors often find more than just a few leaks: duct tape 

dries and falls away; ducts may have been torn or crumpled by other 

trades during installation; and poorly hung ducts can have bends 

and kinks that prevent air from flowing through them. It is not 

uncommon to find one or more ducts completely disconnected 

from their register. 

If return ducts in the heating and air-conditioning system have 

holes, they can draw in hot attic air or cold outside air. As a result, 

the system must work harder and use more energy to heat and cool 

the inside of the house. In older homes, wall cavities and floor joist 

cavities are sometimes used as return “ducts” to bring air from the 

return registers back to the air handler unit, but these building 

cavities are rarely air sealed. 

A heating and cooling equipment contractor may 

•	 Inspect the duct system, including the attic and crawlspace. 

•	 Evaluate the system’s supply and return air flow.

•	 Repair damaged and disconnected ducts. 

•	 Seal all leaks and connections with mastic (a thick sealant 

painted on duct joints). 

•	 Seal all registers and grills to the ducts. 

•	 Insulate ducts in unconditioned areas (like attics, crawlspaces, 

and garages) with duct insulation that has an R-value of 

6 or higher. 

•	 Replace the filter as part of any duct system improvement. 

•	 Retest air flow after repairs are completed. 

•	 Ensure there is no backdrafting of gas or oil-burning appliances, 

and conduct a combustion safety test after ducts are sealed.

When To Do This

Whenever and wherever ducts

are accessible.

Durability & Health

Unsealed ducts can draw in dust, moisture, 

and contamination from unconditioned 

spaces in the home. Broken ducts can 

be a pathway for pests.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

HVAC register boots

HVAC register boots that penetrate 

building envelope are sealed to subfloor

or drywall.

More Information 

•	 Building America Best Practices

•	 Building Science Corporation 2006

•	 Building Science Corporation 2009d

•	 Cummings et al. 1990

•	 Granade et al. 2009

•	 Jump and Modera 1994

•	 Karins et al. 1997

•	 ORNL

•	 Sherman et al. 2000

•	 U.S. Environmental Protection

Agency 2008a

•	 U.S. Environmental Protection

Agency 2009a

April 12, 2010 22

22

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Figure 11.2. Mastic seal all supply and return air ducts.

Studies Show

In a study of energy-efficient measures, DOE’s Energy Information

Administration reported that sealing the ducts yielded by far the greatest 

energy savings of the 12 measures studied, at the lowest cost (Granade

et al. 2009). In a DOE study of 100 homes in Phoenix, Arizona, sealing

ducts cut leakage by 30%, saving homeowners $80 per year. A study of

24 Florida homes found air-conditioning energy use was reduced by 18%

after duct repairs were made (Cummings et al. 1990). A study of a retrofit

project involving 25 apartments in New York found that sealing the HVAC

ducts cut airflow leakage by 92 CFM for supply ducts and 223 CFM for

return ducts with a simple payback of 3 to 4 years (Karins et al. 1997).

Research on six homes in the southwest indicated that 30% to 40% of

the thermal energy delivered to the ducts passing through unconditioned

spaces is lost through air leakage and conduction through the duct walls. 

Sealing and insulating the ducts cut overall duct leakage approximately

64% (Jump and Modera 1994).

REGISTER

Seal all joints in 

boot and elbow

with mastic

Seal boots to sheet 

goods with caulk, 

mastic, or spray foam

Figure 11.1. Paint mastic (a thick, gooey

substance) on to the duct seams

and joints. (Photo source: Habitat for

Humanity Lakeland FL).

DOE studies show duct 

tape fails within months 

(Sherman et al. 2000).

23 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
12. Whole-House Fan 

Penetration at Attic

An insulated cover is provided that is gasketed or 

sealed to the opening from either the attic side 

or ceiling side of the fan.

A whole house fan is a fan installed in the ceiling to help quickly 

cool the house by drawing air into the house through open windows 

on summer mornings and evenings when the outside temperature 

is lower than the indoor temperature. Ideally, the air should be 

ducted to exhaust outside, not into the attic space. During the winter 

months (and in summer when the air conditioner is running), the 

whole house fan is not used. At those times, it represents a potential 

energy loss because it is essentially a large, uninsulated hole in the 

ceiling. Since standard fan louvers do not insulate or seal tightly, a 

cover should be constructed or purchased to air seal and insulate this 

hole from the attic side, the house side, or in case of very hot or cold 

weather, both sides. Homeowners must remember to remove cover(s) 

before operating the fan and to replace cover(s) during seasons when 

the fan is not in use.

Figure 12.2. Install a removable, insulating, air-sealing cover over your whole

house fan (Source: Southface Energy Institute 1999).

When To Do This

When a whole house fan is installed.

Durability & Health

A whole house fan can pull large quantities

of air from the home and, if windows are 

not open, it can easily backdraft a fireplace 

or combustion appliance located in the 

home or attic. Some localities will not 

permit a whole house fan to be installed if 

a furnace is located in the attic or if there 

is a combustion appliance in the home that 

derives its combustion air from either the

attic or the inside of the home unless the 

homeowner 1) encloses the combustion

appliance so that it obtains combustion 

air from outside the home; 2) ducts the

whole house fan directly to the exterior; or 

3) provides a switching device that allows

only one of the appliances (fan or furnace)

to be on at a time (Davis 2001). The whole

house fan should be ducted to the outside 

or adequate ventilation must be provided

in the attic to prevent the attic from being

overpressurized and pushing attic dust into

the house.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Shafts, penetrations

Duct shafts, utility penetrations, knee 

walls and flue shafts opening to exterior

or unconditioned space are sealed.

More Information 

•	 Building America Best Practices 

•	 Davis 2001

•	 DOE 1999

•	 Southface Energy Institute 1999

April 12, 2010 24

24

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
13. Exterior Walls

Service penetrations are sealed.

Your exterior walls may have a surprising number of holes in 

them—for plumbing pipes and vents, electrical wires and conduits, 

electrical fixtures, clothes dryer ducts, and exhaust fans. Holes may 

also have been drilled through the top and bottom plates; ideally, 

these were caulked and sealed during construction as these areas are 

nearly impossible to get to later, unless drywall or exterior sheathing is 

being replaced. Your contractor will caulk penetrations through walls 

from the exterior and interior. An ideal time to seal the drywall to the 

subfloor is when walls are being painted and baseplate trim is removed 

(just pull back the carpet) or when floor covering is being replaced. 

When To Do This

Seal wall penetrations whenever accessible.

Sill- and top-plate penetrations may only

be accessible during construction of new 

walls or additions or when exterior or

interior wall sheathing is being replaced. 

Electrical switches and outlets can be 

accessed any time.

Durability & Health

Unsealed penetrations can be a pathway 

for dust and pests to enter the home. 

Penetrations through the top plate must

be sealed if the top plate is in the plane of 

an intended air, smoke, or fire separation 

(BSC 2009).

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Shafts, penetrations

Duct shafts, utility penetrations, knee 

walls and flue shafts opening to exterior or

unconditioned space are sealed.

Shower/tub on exterior wall

Showers and tubs on exterior walls

have insulation and an air barrier

separating them from the exterior wall.

Electrical/phone box 

on exterior walls

Air barrier extends behind boxes or

air sealed-type boxes are installed.

More Information 

•	 Building America Best Practices

•	 Building Science Corporation 2006

•	 Building Science Corporation 2009e

•	 U.S. Environmental Protection

Agency 2008a

CAULK

Continuous bead of

sealant or adhesive

Thin sheet goods 

as draft stop behind

tub or enclosure

Blocking

– TUB –

CAULK

Exhaust Fan

If fan exhausts or draws air 

through sidewall, install hood

with louvered damper

Caulk around exterior

Figure 13.2. If you are remodeling a

bathroom make sure you seal and 

insulate behind the tub or shower, 

especially if it is on an exterior wall.

Figure 13.1. Caulk all plumbing

penetrations through exterior walls.

Nailing

flange Built-in

sealant

Select boxes with 

built-in gasket 

and sealant

Flange for sealing to 

drywall air barrier

Figure 13.3. Seal all electric outlets and

switches with foam sealant, or select boxes

with built-in sealant or gaskets. Install

foam gaskets between electrical outlets 

or switches and their 

coverplates, and insert

plastic “child-safety”

plugs into the outlets to 

further block airflow.

Figure 13.4. Caulk around exhaust

fans at the ceiling and exterior

wall. Also caulk around exterior

outlets and light fixtures.

Foam Gasket

25 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
14. Fireplace Wall

Air sealing is completed in framed shaft behind 

the fireplace or at fireplace surround.

Fireplaces have many potential areas of air leakage. Air sealing 

and insulation are often missing from the enclosure that forms a 

prefabricated fireplace. There are often unsealed air gaps around the 

flue and the surround. Flue dampers are not airtight, allowing air to 

escape up the chimney even when no fire is burning in the fireplace 

(BSC 2009). A fireplace can actually waste more heat than it creates 

(Iowa Energy Center 2008). 

Even if you close the fireplace damper and it leaks just a little, a lot 

of warm air from your home will be drawn up the chimney and be 

replaced by cold air leaking into the house. If you use the fireplace, 

follow these air sealing tips: (Iowa Energy Center 2008)

•	 Every year, have the fireplace and chimney inspected and cleaned 

by a certified chimney sweep. 

•	 Check the seal of the flue damper with an incense stick or piece of 

burning paper. Seal around the damper assembly with refractory 

cement, but don’t seal the damper closed. Replace warped or 

missing dampers.

•	 Use a removable plug like a chimney balloon that you insert in 

the chimney above the damper and inflate to plug air leaks when 

you’re not using the fireplace. If you forget to remove it before 

starting a fire, it will react to the heat and quickly deflate. 

•	 Install tight-fitting glass doors. 

•	 Make a tight-fitting air barrier to cover the fireplace opening 

when not in use from rigid board insulation and plywood edged 

with pipe insulation (Iowa Energy Center 2008).

•	 Consider installing a sealed, natural gas or propane fireplace 

insert. These inserts are sealed combustion and do away with 

door and flue leaks.

When To Do This

At any time.

Durability & Health

An open, unsealed fireplace carries risks of 

backdrafting carbon monoxide, smoke, and

ash into the home. A sealed fireplace with 

its own combustion air intake is preferred. 

Homes that use gas or wood fireplaces 

should have carbon monoxide detectors.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Fireplace

Fireplace walls include an air barrier.

More Information 

•	 Building America Best Practices

•	 Brown 1999

•	 Building Science Corporation 2009a

•	 Dalicieux and Nicolas 1990

•	 Iowa Energy Center 2008

•	 Tyrol and Pate 2007

•	 U.S. Environmental Protection

Agency 2008a

Figure 14.1. Air seal the enclosure

surround and flue.

Studies Show

Studies have shown that fireplace dampers are often left open. One study

showed found 80% of fireplace dampers were inadvertently left open

(Tyrol and Pate 2007). In a DOE-funded study of 56 new homes in Arkansas

with gas or wood fireplaces, the fireplaces accounted for 5.3% of total

house air leakage (Brown 1999).

Seal

Solid air barrier

material sealed at 

perimeter and seams

April 12, 2010 26

26

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
When To Do This

At any time.

Durability & Health

Garages often contain harmful chemicals

and gases that must be kept out of the 

living space by thorough air sealing of any

common walls and ceilings.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Garage separation

Air sealing is provided between the

garage and conditioned spaces.

More Information 

•	 Building America Best Practices

•	 Aspen Publishers 2000

•	 Iowa Energy Center 2008

•	 University of Illinois Extension Office

•	 U.S. Environmental Protection

Agency 2010

15. Garage/Living Space Walls

Air sealing is completed between garage and living space. 

Pass-through door is weather stripped.

For occupant health and safety, the garage should be completely air 

sealed from the living areas of the house. When the garage is beneath a 

second-story living space, the gaps created by the floor joists spanning 

both the living space and the garage must be blocked off and sealed. 

If the air handler for a central furnace must be located in the garage, 

it should be in an air-sealed closet with its own air intake, so that it is 

not drawing garage air to circulate through the house. 

If you have an attached garage, expect your contractor to visually 

inspect for cracks or improper sealing of the walls separating the 

garage from the home, to test the seal tightness of doors linking the 

garage with the rest of the home, to test carbon monoxide levels in the 

house, to measure interface leakage between the garage and house, 

and to determine what size garage exhaust fan, if any, is advisable. 

Steps to a Healthier Garage – eliminate, isolate, ventilate.

Keep in mind the following:

1. Your very best option is to build a detached garage.

2. If that is not possible, try removing or isolating pollutants. Park 

cars, mowers, etc., outside. Do not let cars or mowers idle in the 

garage (and of course never start them with the garage door 

closed). Start gas-powered mowers, leaf blowers, etc., outside. 

Store paints, solvents, and other chemicals in tight containers. 

Your contractor can assist you with the following recommendations:

3. Seal all penetrations through the common wall and ceiling. Use 

gaskets, airtight drywall technique, etc., to make the common wall 

and ceiling airtight.

4. Seal ducts located in the garage. (Avoid locating supply or return 

registers in the garage when remodeling.) 

5. Install a self-closing, insulated, metal, fire-rated door with a good 

weather seal between the living space and the garage. 

6. Install a passive roof vent to keep the garage at a negative pressure 

in relationship to the house. If needed, install a timed exhaust fan 

that vents to the outside.

27 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Figure 15.1. Finish the walls that separate the garage from the rest of the home

with drywall that is sealed to the top and bottom plate with a bead of caulk. 

Studies Show

In a field study of 12 homes in Anchorage, Alaska, researchers found that

carbon monoxide (CO) from car starts in the garages entered all but 1 of

the 12 houses. Four of the homes came close to the EPA CO exposure limit

and, in one case, exceeded it (Aspen Publishers 2000). Noted the author:

“In all but one case, the house was operating under negative pressure

relative to the garage due to the stack effect. In other words, the house

was sucking CO and other airborne contaminants through the common

walls and ceilings.” The researchers found high CO in homes where

furnace ductwork was located in the garage and where the garage was 

located under occupied space above. A study by Health Canada identified

150 different pollutants commonly found in garages. Preliminary results

from 25 houses tested in that study found that an average of 13% of all

infiltration into the houses was through the common wall between the 

garage and house. A Minnegasco study measured typical leakage at an 

even higher 25% (Aspen 2000).

Bottom plate caulked

or gasketed to subfloor

Drywall caulked, glued 

or gasketed to top plate

GARAGE

15.2. Seal rim joists of the wall separating

the house’s living space from the garage

with pieces of wall board and spray foam.

April 12, 2010 28

28

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
When To Do This

When comfort complaints or high utility 

bills warrant it; if an infrared camera 

inspection reveals the cantilever floor

to be a source of high leakage.

Durability & Health

If a cantilever isn’t properly air sealed

and insulated, moist air from the home 

can pass into the cantilever floor cavity

and condense on the coldest surface it 

finds—the backside of the sheathing or

band joist—causing mold to grow there.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Floors (including above-garage 

and cantilevered floors)

Insulation is installed to maintain 

permanent contact with underside of 

subfloor decking. Air barrier is installed

at any exposed edge of insulation.

More Information 

•	 Building America Best Practices 

•	 Lugano 1998

•	 U.S. Environmental Protection

Agency 2008b

16. Cantilevered Floor

Cantilevered floors are air sealed and insulated at perimeter 

or joist transitions.

Cantilevered floors, second-story bump-outs, and bay windows are 

another area in the home that is often lacking proper air sealing. 

The floor cavity must be filled with insulation with good alignment 

(i.e., that is completely touching) the underside of the floor. The 

interior and exterior sheathing needs to be sealed at the framing 

edges. Blocking between floor joists should form a consistent air 

barrier between the cantilever and the rest of the house. Continuous 

sheathing, such as insulating foam sheathing, should cover the 

underside of the cantilever, and be air sealed at the edges with caulk. 

Figure 16.1. Block and

air seal both the floorto-upper wall junction

and the floor-to-lower

wall junction.

Baseplate sealed 

to subfloor

Blocking between joists,

sealed at perimeter

Insulation in continuous

contact with subfloor

29 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
17. Rim Joists, Sill Plate, Foundation, 

and Floor

Rim joists are insulated and include an air barrier. Junction 

of foundation and sill plate is sealed. Penetrations through 

the bottom plate are sealed. All leaks at foundations, 

floor joists, and floor penetrations are sealed. Exposed 

earth in crawlspace is covered with Class I vapor retarder 

overlapped and taped at seams.

The rim joist (also called a band joist) is the horizontal beam that 

rests on top of the foundation wall or between floors. The floor joists 

are attached to or run parallel with it. Rim joists are a particularly 

troublesome area for air leakage. Several framing components 

(foundation wall and sill plate or top plate, rim joist, and subfloor 

above) need to be connected and sealed to form a continuous air 

barrier. Your contractor will inspect this area and, if needed, air seal 

and insulate along the joints where the floor joists meet the rim joist 

and the rim joist meets the subfloor. The rim joist can be air sealed 

and insulated with caulk and batt insulation, or rigid foam cut to 

fill the space between each floor joist and sealed in place with spray 

foam. Another option is to spray high- or low-density urethane 

foam at each joist bay to cover the foundation wall-top plate-rim 

joist-subfloor connections. 

Figure 17.1. Use caulk or spray foam to air seal where the foundation wall meets

the sill plate, where the sill plate meets the rim joist, and where the rim joist 

meets the subfloor. 

When To Do This

Air sealing rim joists below the first floor

can be done in conjunction with finishing 

the basement, when insulating the 

basement walls, or whenever an unsealed

rim joist is accessible from inside. Plywood

subfloor seams can be sealed when

replacing flooring or replacing or

installing insulation beneath the floor.

Durability & Health

The interior side of the rim joist is a cold

surface in wintertime; condensation can 

form there if it is not properly insulated. 

A dirt crawlspace floor should be covered

with a Class 1 vapor retarder (e.g., 6-mil

polyethylene). If the home has an unvented

crawlspace, the underside of the floor

should be air sealed and a vent stack can

be installed to minimize entry of soil gases 

into living space.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Walls

Junction of foundation and sill

plate is sealed.

Corners and headers are insulated.

Rim joists

Rim joists are insulated and include

an air barrier.

Crawlspace walls

Exposed earth in unvented crawlspaces

is covered with Class I vapor retarder

with overlapping joints taped.

Tape

Rim Joist

Seal outside if it can 

be done without interfering 

with drainage

Housewrap Drywall

Bottom Plate

Caulk

Sill Plate

– Floor Joist –

Sill gasket

Subfloor

April 12, 2010 30

30

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
Studies Show

One homeowner in Illinois had spent thousands of dollars re-siding his

house with rigid foam insulation, adding insulation, upgrading his furnace, 

and replacing windows but his house was still drafty and his utility bills 

were still high. He called in a BPI-certified contractor who conducted several

assessments including a blower door test of the whole house and individual

rooms to determine where air was leaking. The blower door showed the

home’s air leakage was three times higher than preferred. The contractor

recommended plugging leaks in the crawlspace and rim joists; adding joist 

insulation; air-sealing all plumbing, electrical, service, and duct penetrations;

and insulating and air sealing the crawlspace access and attic hatch cover.

The upgrades cost $2,500 and saved the homeowner $700 a year in energy

costs (Conbere and Fried 2006).

More Information 

•	 Building America Best Practices

•	 Building Science Corporation 2009c

•	 Conbere and Fried 2006

•	 Braun 1995

•	 Building Science Corporation 2009e

•	 Lstiburek 2004a, b; 2006; 2008

•	 U.S. Department of Energy 2000a

•	 U.S. Environmental Protection

Agency 2008b

•	 U.S. Environmental Protection

Agency 2009b

•	 U.S. Environmental Protection

Agency 2009c

Your contractor will seal the seams of the subfloor plywood panels 

if they are accessible. The contractor will also seal all holes that go 

through the basement ceiling to the floor above, such as holes for 

plumbing, HVAC ducts, and furnace vent pipes if the furnace is 

located in the basement.

If your house’s foundation is a slab, your contractor can check 

for and seal air leaks where the sill plate meets the foundation. If 

your home has an unvented crawlspace your contractor will check 

the foundation for cracks and holes that may need sealing. The 

crawlspace access hatch should be weather stripped or gasketed. If 

the crawlspace floor has exposed earth, this should be covered with 

Class I vapor retarder with overlapping joints that are taped.

Air seal gasket

Crawlspace

Rigid insulation

Figure 17.3. Air seal the crawlspace access hatch by installing a gasket

or weather stripping around the hatch edges. 

Figure 17.2. Spray foam along the basement

rim joist to provide a complete air barrier

connecting the foundation wall, sill plate, 

rim joist, and subfloor (Source: BSC 2009C).

31 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
18. Windows and Doors

Space between window/door jambs and framing is sealed.

When windows are installed in a new house, the rough opening (the 

space left for the window) is typically 1.5 to 2 inches larger than the 

window frame to give the installer room to install, plumb, and square 

the window. The same is true of doors. Your contractor can properly 

seal around the existing windows by removing the interior trim and 

filling the rough opening with non-expanding foam or backer rod and 

caulk. A simpler but more visible alternative is to leave the interior 

trim in place and seal around it with a clear silicone caulk or paintable 

latex caulk with silicone. Replace any cracked or loose panes. Consider 

replacing older, single-pane windows that show signs of leakage, water 

damage, or condensation with new double-pane windows installed 

with proper air sealing and flashing.

Windows and doors should be weather stripped. See the DOE Energy 

Savers website for a comprehensive description of different types 

of caulking and weather stripping material www.energysavers.gov/

your_home/insulation_airsealing/index.cfm/mytopic=11260. 

Older homes often have double-hung windows with chases hidden in 

the wall for counter weights. Access these chases by removing the side 

trim or by going through access ports along the sides of the window. 

If the window is replaced, the weight should be removed and the 

chases filled with insulation and sealed. If you have old windows with 

working pulleys, the pulley holes can be air sealed but kept usable with 

plastic caps called pulley seals. Doors should be self-closing and have 

a tight fitting sill.

When To Do This

Any time.

Durability & Health

More efficient windows may be less prone

to condensation and related mold growth. 

Painted window sashes and frames in

homes built before 1978 may contain leadbased paint; use a contractor experienced

in lead removal.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Windows and doors

Space between window/door jambs 

and framing is sealed.

More Information 

•	 Building America Best Practices 

•	 Building Science Corporation 2009b

•	 Stovall et al. 2007

•	 U.S. Department of Energy 2000a

U.S. Department of Energy 2009c

•	 U.S. Environmental Protection

Agency 2008b

Studies Show

A study conducted at Oak Ridge

National Laboratory’s Buildings

Technology Center on window

air sealing showed that windows 

with 3⁄4-inch rough-in gaps had an

equivalent leakage area of 28.2 cm2/

m2

. When the gap was caulked from 

the interior side of the wall, the 

equivalent leakage area was cut to

0.5 cm2/m2 (Stovall et al. 2007).

backer rod, caulk,

or nonexpanding foam

Use ENERGY STAR

labeled door

Install automatic

closer and gasket

or weatherstripping

Figure 18.1. Use backer rod, caulk,

or nonexpanding foam approved

for windows and doors to fill the 

rough-in gap around doors and

windows (DOE 2000).

Figure 18.2. Install automatic closer

and gasket or weather stripping 

around doors. Caulk around trim.

April 12, 2010 32

32

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
19. Common Walls Between 

Attached Dwelling Units

The gap between a gypsum shaft wall (i.e., common wall) 

and the structural framing between units is sealed.

Common walls between units in multi-family housing (e.g., 

townhouses, duplexes, and apartments) should be constructed as 

airtight assemblies for sound, smoke, fire, and air quality control. 

However, experience has shown that these common walls can often 

be significant sources of air and heat loss if gaps or cracks exist in the 

connections between each unit’s walls. Your contractor can determine 

whether this is a significant source of air leakage in your home.

To reduce air leakage, this assembly should be air sealed at all 

boundaries. Your contractor will seal wood frame walls with 

fireproof spray foam (EPA 2008). Masonry block party walls, which 

form “chimneys” because of their porosity and open cores, can be 

air sealed with two-component urethane foam, which also reduces 

sound, odor transfer, and dust, insects, and moisture entry 

(Braun et al. 1995).

Because these walls are fire-rated assemblies for each unit, acceptable 

materials for air-sealing common walls can vary significantly 

around the country. Your contractor will confirm with local code 

officials which material is preferred for fire safety reasons, prior 

to retrofitting. The contractor will seal all plumbing penetrations 

through the drywall surface of common walls with fire-rated sealant 

materials (BSC 2009).

Figure 19.1. Seal air gaps 

between two framed common 

walls (Source: Energy Services 

Group, from EPA 2008)

When To Do This

Whenever common wall is accessible.

Durability & Health

Common walls between units are fire-rated

and should be air sealed and properly 

blocked to minimize fire spread and entry 

of air, moisture, and pests.

2009 IECC/2009 IRC Code

Requirement for New 

Construction and Additions

Common wall

Air barrier is installed in common 

wall between dwelling units.

More Information 

•	 Braun and Woods 1995

•	 Building Science Corporation 2009e

•	 U.S. Environmental Protection

Agency 2008b

33 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
References

Aspen Publishers 2000. “How Attached Garages Poison Our Indoor Air, And What Builders Can Do About It.” in Energy Design Update, Volume 20,

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35 April 12, 2010

RETROFIT TECHNIQUES AND TECHNOLOGIES AIR SEALING
EERE Information Center 

1-877-EERE-INF (1-877-337-3463) 

www.eere.energy.gov/informationcenter

PNNL-19284 April 12, 2010

For information on Building America 

visit www.buildingamerica.gov. 

The website contains expanded 

case studies, technical reports, and 

best practices guides.

Building America Program

George S. James • New Construction • 202-586-9472 • fax: 202-586-8134 • e-mail: George.James@ee.doe.gov

Lew Pratsch • Existing Homes • 202-586-1512 • fax: 202-586-8185 • e-mail: Lew.Pratsch@ee.doe.gov

Building America Program • Office 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)

Philip Fairey • Florida Solar Energy Center • 1679 Clearlake Road • Cocoa, FL 32922 • 321-638-1005 • 

fax: 321-638-1439 • e-mail: pfairey@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

Pacific Northwest National Laboratory

Michael Baechler • 620 SW 5th, Suite 810 • Portland, OR 97204 • 503-417-7553 • fax: 503-417-2175 • 

e-mail: michael.baechler@pnl.gov • www.pnl.gov

Produced for the U.S. Department of Energy (DOE) by Pacific Northwest National Laboratory, 

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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 significant.

DOE’s Building Technologies 

Program works to improve the 

energy efficiency 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 energyefficient components, materials, 

and equipment

• Technology Integration of new 

technologies with innovative 

building methods to optimize 

building performance and savings

Visit our Web sites at:

www.buildingamerica.gov

www.pathnet.org

www.energystar.gov

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