AIR SEALING

Seal air leaks and save energy!

WHAT IS AIR LEAKAGE?

Ventilation is fresh air that enters a house in a

controlled manner to exhaust excess moisture

and reduce odors and stuffiness. Air leakage,

or infiltration, is outside air that enters a house

uncontrollably through cracks and openings. It

is unwise to rely on air leakage for ventilation.

During cold or windy weather, too much air

may enter the house and, during warm or calm

weather, too little. Also, a leaky house that

allows moldy, dusty crawlspace or attic air to

enter is not healthy.

The recommended strategy in both new and old

homes is to reduce air leakage as much as possible and to provide controlled ventilation as

needed. For simple house designs, effective spot

ventilation, such as kitchen and bath fans that

exhaust to the outside, may be adequate. For

more complex houses or ones in colder

climates, whole house ventilation systems may

be appropriate. Such systems may incorporate

heat recovery, moisture control, or air filtering.

noise, dust, and the entry of pollutants, insects,

and rodents. Reducing infiltration can significantly cut annual heating and cooling costs,

improve building durability, and create a

healthier indoor environment. The size of heating and cooling equipment can also be decreased, which saves additional dollars. Reducing air leakage in new homes, as required by the

1995 Model Energy Code (see page 4), typically

costs less than $200 for the average home and

does not require specialized labor.

Buildings for

the 21st Century

Buildings that are more

energy-efficient, comfortable,

and affordable...that’s the

goal of DOE’s Office of Building

Technology, State and

Community Programs (BTS).

To accelerate the development

and wide application of energy

efficiency measures, BTS:

• Conducts R&D on technologies and concepts for energy

efficiency, working closely

with the building industry

and with manufacturers of

materials, equipment, and

appliances

• Promotes energy/money

saving opportunities to both

builders and buyers of homes

and commercial buildings

• Works with State and local

regulatory groups to improve

building codes, appliance

standards, and guidelines for

efficient energy use

• Provides support and grants

to States and communities

for deployment of energyefficient technologies and

practices

Technology Fact Sheet

Bath Fan

Kitchen

Range

Hood

Kitchen and bath vents provide spot ventilation

 Annual Energy Costs for 1300 sq. ft. house

Infiltration rate Savings

Atlanta High* Low**

Heating $311 $244 $67

Cooling $196 $178 $18

* Estimated 12 air changes per hour at 50 Pascal pressure difference

** Estimated 6 air changes per hour at 50 Pascal pressure difference

WHAT ARE THE BENEFITS OF AIR

SEALING?

Air infiltration can account for 30 percent or

more of a home’s heating and cooling costs

and contribute to problems with moisture,

WHAT IS AN

AIR BARRIER?

The ceilings, walls,

and floor/foundation

that separate the

inside conditioned

space from the outside or unconditioned space form the air barrier and the

insulation barrier for a house. These two

barriers differ by the materials used.

For most homes, the sheet goods that form the

ceilings, walls, and floor (such as drywall,

sheathing, and decking) are effective at stopping

air leakage. It is critical to seal all holes and

seams between these sheet goods with durable

caulks, gaskets, and foam sealants to create a

continuous air barrier. The insulation barrier is

usually made up of standard insulating materials, such as batt or loose fill products, that do

not seal against air leakage.

OFFICE OF BUILDING TECHNOLOGY, STATE AND COMMUNITY PROGRAMS

ENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY
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WHAT ARE THE PRIORITIES FOR AIR SEALING?

Although windows, doors, and outside walls contribute to air

leakage, the biggest holes are usually hidden from view and

connect the house to the attic, crawlspace, or basement. The

key is to identify these areas during the design process, assign

responsibility for sealing holes, and check to ensure that the air

sealing was done effectively. Usually, seal all the big

holes first, then the large cracks and penetrations, and

finally the smaller cracks and seams.

WHERE ARE THESE LEAKAGE SITES?

Dropped ceilings and kitchen soffits, ductwork and

plumbing chases, attic accesses and pull-down stairs,

recessed light fixtures, holes in mechanical room closets,

and wiring penetrations through the top plates of walls

represent major connections between the attic and conditioned space. Many times unseen holes or pathways,

called bypasses, occur at key junctures in the framing

(such as at attic-to-kneewall transitions) and permit large

quantities of air to leak in and out of the home.

Major leakage sites in the floor can be found around

the tub drain and the numerous plumbing, HVAC, and

wiring penetrations through the floor decking and bottom

plates of walls. In walls, the band joist (for two-story homes),

window and door rough openings, and penetrations through

the drywall and exterior sheathing are primary leakage sites.

AI R SE A L I N G MATERIALS

Use a combination of these different air sealing materials.

• Caulk: Seals gaps of less than 1⁄2". Select grade (interior,

exterior, high temperature) based on application.

DON’T RELY ON THE INSULATION:

The most common insulation, fiberglass, does not stop

air leakage. In older homes, dirty fiberglass is a telltale

sign of air movement (it simply collects dirt like a filter).

Certain types of insulation, such as dense-packed cellulose and certain foams, can be effective at reducing air

flow as well as heat flow.

• Spray foam: Fills large cracks and small holes. It can be

messy; consider new latex-based foams. DO NOT USE near

flammable applications (e.g., flue vents). DO NOT USE

expanding types on windows and doors.

• Backer rod: Closed-cell foam or rope caulk. Press into crack or

gap with screwdriver or putty knife. Often used with caulk

Use backer rod to fill gaps between

window and rough opening before

caulking or use non-expanding

foam.

DIAGNOSTIC TOOLS

Testing the airtightness of a home using a special fan called

a blower door can help to ensure that air sealing work is effective. Often, energy efficiency incentive programs, such as the DOE/

EPA ENERGY STAR Program, require a blower

door test (usually performed in less than an

hour) to confirm the

tightness of the house.

Exterior

door frame

Temporary covering

Adjustable frame

Air pressure gauge

Fan

around window and door rough openings.

• Gaskets: Apply under the bottom plate before

an exterior wall is raised or use to seal drywall

to framing instead of caulk or adhesive.

• Housewrap: Installed over exterior sheathing.

Must be sealed with housewrap tape or caulk

to form an airtight seal. Resists water but is

not a vapor barrier.

• Sheet goods (plywood, drywall, rigid foam insulation): These materials form the air barrier. Air

leaks only at unsealed seams or penetrations.

• Sheet metal: Used with high-temperature caulk

for sealing high-temperature components,

such as flues and chimneys, to framing.

• Polyethylene plastic: This inexpensive material for air

sealing also stops vapor diffusion. All edges and penetrations must be completely sealed for an effective air barrier.

Poly is fragile, and proper placement is climate specific.

• Weatherstripping: Used to seal moveable components,

such as doors, windows, and attic accesses.

• Mastic: Seals air handlers and all duct connections and

joints.

• UL181 or foil-faced tape: Temporarily seals the air

handler.
AIR SEALING

Seal and insulate exterior wall before installing bath tubs.

Seal dropped soffit ceilings, plumbing and electrical penetrations, and utility chases. Seal exterior sheathing joints, and top and bottom plates.

Seal kneewall to create a continuous air barrier.



yyyyyy

Seal

chases

Sheet

metal 

and 

high-temp

caulk

Seal

bottom

plate

Seal HVAC

penetrations

Seal electrical

penetrations

Seal and insulate

dropped soffit

Seal plumbing

penetrations

Caulk 

electrical

fixtures to 

drywall

Seal

Attic

living

space

Seal

Hardboard

Unwanted 

air leakage

Attic Ventilation

Knee wall

Seal

outlet

box to

drywall

Seal all edges of rigid 

foam insulation 

Attic space

Desired 

ventilation

Option 1

Option 2



yyyyyy

Caulk bottom plate

to subfloor

Tape or 

caulk exterior 

sheathing

seams 

Rafter 

baffle

Soffit vent

Attic 

ventilation

Sheathing – 

OK to extend 

sheathing 

below sill plate

Caulk drywall to 

top and bottom 

plates

Sill gasket or 

double-bead of caulk

Caulk band joist

to subfloor and plates

Caulk bottom plate 

to subfloor 

Seal tub penetration

Seal plumbing 

and 

electrical 

penetrations

Insulate and air seal 

behind tub with sealed polyethylene 

plastic or sheet material

Exterior wall
For more information, contact:

Energy Efficiency and

Renewable Energy

Clearinghouse (EREC)

1-800-DOE-3732

www.eren.doe.gov

Or visit the BTS Web site at

www.eren.doe.gov/buildings

Or refer to the Builder’s Guide

Energy Efficient Building

Association, Inc.

651-268-7585

www.eeba.org

Written and prepared for

the U.S. Department of

Energy by:

Southface Energy Institute

404-872-3549

www.southface.org

Oak Ridge

National Laboratory

Buildings Technology Center

423-574-5178

www.ornl.gov/ornl/btc

The Model Energy Code

can be obtained from the

International Code Council by

calling 703-931-4533

MECcheck, a companion

compliance software

package, can be ordered from

DOE by calling

1-800-270-CODE

or downloaded directly

from the Web at

www.energycodes.org/

resid/resid.htm.

AIR SEALING

NOTICE: Neither the United States government nor any agency thereof, nor

any of their employees, makes any warranty, express or implied, or assumes

any legal liability or responsibility for the

accuracy, completeness,

or usefulness of any information, apparatus, product, or process disclosed.

The views and opinions of authors expressed herein do not necessarily state

or reflect those of the United States

government or any agency thereof.

AIR SEALING CHECKLIST

BEFORE DRYWALL

• Seal bottom plate of exterior walls with

caulk or gasket; seal inside edge with

caulk after walls are up.

• Seal band joist with caulk, spray foam, or

gasketing between top plate and band

joist, and between band joist and subfloor.

• For bath tubs on outside walls, insulate

the exterior wall and air seal behind tub

with sheet goods or plastic before tub is

installed. After the drain is installed, seal

the tub drain penetration with sheet

goods and caulk or spray foam.

• For dropped ceilings or soffits, duct and

flue chases, and open partition walls,

use sheet goods and sealant to stop air

leakage from attic into soffit and then insulate. Alternately, install framing and

drywall for the soffits after the taped ceiling drywall is installed.

• Caulk the backsides of window flanges to

the sheathing during installation.

• Seal between door thresholds and

subflooring with caulk.

• Seal window and exterior door rough

openings with backer rod and caulk, or

use non-expanding latex-based spray

foams that will not pinch jambs or void

window warranties.

• Seal all electrical wire, plumbing, and

HVAC penetrations between any conditioned and unconditioned spaces with

caulk or spray foam.

• Seal wiring and knockouts in electrical

boxes with caulk. Also seal outdoormounted boxes to the exterior sheathing.

DURING DRYWALL

• Seal drywall to top and bottom plates

using gaskets, adhesive, or caulk.

AFTER DRYWALL

• Seal electrical switch, outlet, and circuit

breaker boxes to drywall with caulk or

foam.

• Seal light fixture boxes, medicine

cabinets, and bath and kitchen ventilation fans to drywall with caulk or foam.

• Seal all duct boots to floor or drywall

with caulk, foam, or mastic.

• Seal any plumbing or electrical wire penetration through drywall with caulk or foam.

• Seal gaps at whole house fan with spray

foam or housewrap tape (ensure louvers

function properly).

• For attic hatches and kneewall access

doors, weatherstrip and include a tight

latch. Add rigid insulation.

• For attic pull-down stairs, make stairs airtight using latch bolts and

weatherstripping. Add an insulated cover.

• Seal between a masonry chimney and the

attic framing using sheet metal or other

noncombustible sheet goods and

high-temperature (450°F), fire-rated caulk.

• Seal around the metal flue of combustion

equipment using a UL-approved metal

collar and high-temperature (450°F),

fire-rated caulk.

• Use only UL-approved airtight, IC-rated

recessed light fixtures (that meet ASTM

E283 requirements); seal between fixture

and drywall with caulk.

AI R SEAL EXTERIOR

• Repair any damaged sheathing pieces.

• Seal all exterior penetrations, such as

porch light fixtures, phone, security,

cable and electric service holes, with

caulk or spray foam.

• If not using housewrap, seal all sheathing seams with housewrap tape or caulk.

Printed with a renewable-source ink on paper containing at

least 50% wastepaper, including 20% postconsumer waste.

November 1999 DOE/GO10099-767