Air leakage, or infiltration, is a major problem in both new and older homes. Besides wasting hundreds of dollars on energy bills, air leakage paths can cause building durability problems, increase the risk of fire spread, permit insect and rodent entry, and create unhealthy indoor air quality. Reducing air leakage usually adds little to the materials' cost of a house and does not require specialized labor.
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.
Great Care Should be Taken to Seal the Following Areas:
- any openings or cracks where two walls meet, where the wall meets the ceiling or near interior door frames
- gaps around electrical outlets, switch boxes and recessed fixtures
- gaps behind recessed cabinets and furred or false ceilings such as kitchen or bathroom soffits
- gaps around attic access hatches and pull-down stairs
- behind bath tubs and shower stall units
- through floor cavities of finished attics adjacent to unconditioned attic spaces
- utility chase ways for ducts, etc., and plumbing and electrical wiring penetrations
(“Insulating a New Home: Do It Right the First Time”. Building Envelope Research; Insulation Fact Sheet. Accessed 1 April 2009.)
What Materials are Available to Seal a Home?
- Caulk: Use to seal gaps less than ½". Select grade (interior, exterior, high temperature) based on application.
- Spray foam: Expands to fill large cracks and small holes. It can be messy; consider new, water-based foams. NOT recommended near flammable applications (flue vents, etc.).
- Backer rod: Closed cell foam or rope caulk. Press into crack or gap with screwdriver or putty knife. Often used with caulk around window and door rough openings.
- Gaskets: Can be applied under the bottom plate before an exterior wall is raised, or used to seal drywall to framing.
- Housewrap: Installed over exterior sheathing. Must be sealed with tape or caulk to form an airtight seal. Resists liquid water but is not a vapor barrier.
- Sheet goods (plywood, drywall, rigid foam insulation): These are the solid materials which form the building envelope. Air will only leak at the seams or through unsealed penetrations.
- Sheet metal: Used with high temperature caulk for sealing high temperature components, such as flues, to framing.
- Polyethylene plastic: Inexpensive material for airsealing that also stops vapor diffusion. Must have all edges and penetrations sealed to be effective air barrier.
- Weatherstripping: Used to seal moveable components, such as doors and windows.
**Don’t Rely on the Insulation! The most common insulation, fiberglass, does not stop air leakage. In older houses, dirty fiberglass is a telltale sign of air movement (it simply acts as a filter). (Certain types of insulation, such as dense-packed cellulose and urethane foams, can be effective at reducing air flow.)
What Must Be Air Sealed?
Airsealing does not usually require expensive materials or special construction skills. However, airsealing must be done throughout the construction process: during framing, prior to insulating and installation of interior finish materials, after installation of fixtures, and as a part of final punch-out. The materials that form the air barrier must be designed to provide a seal that will last the life of the home or be easily re-applied by the home owner.
Before drywall:
- Seal bottom plate of exterior walls with caulk or sill seal; seal inside edge with caulk after walls are up.
- Seal band joist area 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 before tub is installed. After the drain is installed, seal the tub drain penetration with rigid foam insulation and spray foam.
- For dropped soffit cabinets and showers, use sheet material and sealant to stop air leakage from attic into soffit and then insulate. Alternately, frame and install drywall for the soffit area after the taped ceiling drywall is installed.
- Seal windows and exterior doors with backer rod and caulk or spray foam. Be cautious using spray foam as it can expand and pinch jambs and may void some window warranties.
- Seal all electrical wire, plumbing, and HVAC penetrations between any conditioned and unconditioned spaces.
After drywall:
- Seal electrical switch and outlet boxes to drywall with caulk.
- Seal light fixture boxes to drywall with caulk or foam.
- Seal 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 penetration through drywall with caulk or foam.
- If not done before drywall, seal tub drain penetration (from crawlspace side) with plywood or rigid board insulation and caulk or foam.
- For attic hatches, insulate top of board with at least two inches of rigid foam insulation or fiberglass batt; seal with weatherstripping. Use these same steps for short and full-size attic kneewall access doors and include a tight latch.
- For attic pull down stairs, use rigid foam cover kit; make stairs airtight using latch bolts and weatherstripping.
Air Seal exterior:
- Seal all exterior penetrations, such as porch light fixtures, phone, security, cable and electric service holes, with caulk or spray foam.
- Repair or replace any missing sheathing.
If installing housewrap:
- Seal top and bottom edges past the plates with housewrap tape or caulk.
- Seal housewrap at windows and doors.
- Minimize cuts in housewrap and caulk or tape to seal all penetrations.
- Overlap seams and seal with caulk or housewrap tape.
- If not using housewrap, seal all sheathing seams with housewrap tape or caulk.
(“Air Sealing: Seal Air Leaks and Save Energy!”. Building Envelope Research; Insulation Fact Sheet. Accessed 24 July 2009.
Two really great tools for both affiliates and volunteers are the ENERGY STAR Air Sealing Critical Details Checklist and the ENERGY STAR Air Sealing "Good vs. Bad" Example Chart. Both are not only good for educating a volunteer with little or no air sealing experience, but also to ensure that an affiliate or builder stays on track to constructing an air-tight and affordable home.