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Air Leakage Control

movement of air, moisture, through a house.

A careful homeowner can seal obvious cracks and gaps with spray foam or caulk and add insulation in the attic, basement, crawl space or open walls. However, insulation needs proper air-sealing to work well. Without the necessary training and equipment, you won't know where your air-leakage is, or if you are creating a combustion safety problem. If you decide to do the work yourself we suggest hiring a contractor with a blower door to help you locate air leaks and check for combustion appliance backdrafting after the work is completed.

Identify Air Leakage

First, make a list of obvious air leaks (drafts). The potential energy savings draft reduction may range from 5% to 30% per year, and the home is generally much more comfortable afterwards.

Look for gaps along:

  1. baseboard or edge of the flooring
  2. junctures of the walls and ceiling
  3. pipes and wires
  4. electrical outlets
  5. foundation seals
  6. mail slots
  7. caulking and weatherstripping

Feel for air flow through:

  1. electrical outlets
  2. switch plates
  3. window frames
  4. baseboards
  5. weather-stripping around doors
  6. fireplace dampers
  7. attic hatches
  8. wall- or window-mounted air conditioners

Most homeowners are aware that air leaks into their houses through what seem to be small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawl spaces. The air travels through any openings in your walls, floors, or ceilings, such as cracks where two walls meet, where the wall meets the ceiling, or near interior door frames. Other openings may also be found, such as gaps around electrical outlets and switch boxes, recessed fixtures, recessed cabinets, pull-down stairs, furred or false ceilings such as kitchen or bathroom soffits, behind bath tubs and shower stall units, floor cavities of finished attics adjacent to unconditioned attic spaces, and plumbing connections. These leaks between the living space and other parts of the house are often much greater than the obvious leaks around windows and doors.


Since many of the leakage paths are driven by the tendency for warm air to rise and cool air to fall, the attic is often the best place to stop them. It isimportant to stop these leaks before adding attic insulation because the insulation may hide them and make them less accessible. Usually, the attic insulation itself will not stop these leaks and you won't save as much as you expect because of the air flowing through the insulation. Sometimes these leak locations are visible because the existing insulation has been stained by dust carried by the air flow. Some of the openings to look for include:

Top openings of interior partition wall cavities: staple a plastic sheet over the opening and seal it around the edges with a high quality caulking material.

Around the chimney: pack gaps around an insulated chimney with UNFACED rock wool or UNFACED fiber glass insulation. Do not insulate bare, hot flue pipes. DO NOT USE ANY COMBUSTIBLE PRODUCTS, SUCH AS CELLULOSE INSULATION OR PLASTIC FOAMS, HERE.

Around the attic trap door or entry door: weatherstrip the edges.

Areas above staircase ceilings and dropped ceilings: staple a plastic sheet over the opening and seal it around the edges with a high quality caulking material.

Around pipes (look under your sinks and behind your toilets) and ducts penetrating a wall or attic floor: pack insulation tightly into the gap. You can also fill the area around them with spray polyurethane foam.

Sometimes joints between walls and floors allow open passage of air between the heated part of the house and the attic area or outdoors. Look for such joints in your attic or in the space over a porch ceiling. This air leakage path is commonly found in Cape Cod-type houses, or if attic space has been converted to living space (see 2D in Fig. 1). A similar arrangement occurs when the second floor of a two-story house is larger than the ground floor and has an overhang over the outdoors (see 4D in Fig. 1). Another major source of air leakage can be the joint between a porch roof and a side wall. If you can reach these areas, you can stop the leaks by carefully covering the openings with plywood. If the areas are more difficult to reach, you can greatly reduce the air leakage by blowing high-density insulation or injecting plastic foam insulation into these joints, thus reducing these energy-gobbling air paths.

If you are having difficulty locating leaks, you may want to conduct a basic building pressurization test. First, close all exterior doors, windows, and fireplace flues. Turn off all combustion appliances such as gas burning furnaces and water heaters. (Remember to turn them back on when you are done with the test.) Then turn on all exhaust fans (generally located in the kitchen and bathrooms) or use a large window fan to suck the air out of the rooms. This increases infiltration through cracks and leaks, making them easier to detect. You can use incense sticks or your damp hand to locate these leaks. Moving air causes the smoke to waver, and you will feel a draft when it cools your hand.

Common Areas of Air Leakage


  1. Drafty windows and doors
  2. Holes or chases that lead down into the house from the attic
  3. Holes or chases that lead up into the house from the basement
  4. Gaps around plumbing and electrical penetrations
  5. Gaps around the dryer vent
  6. Air leaks around the bathroom or kitchen fan vents
  7. Air leaks around recessed lights
  8. Drafty attic door or hatch
  9. Unsealed chases that open to the attic
  10. Gaps around the chimney or furnace flue
  11. Open fireplace dampers.
  12. Tops of walls that open into the attic space


  1. areas where two different building materials meet
  2. holes or penetrations for faucets, pipes, electric outlets, and wiring
  3. cracks and holes in the mortar, foundation, and siding
  4. failed or missing exterior caulking around doors and windows
  5. loose exterior storm doors and primary doors

Precautions and Preparation

  1. Carefully follow the manufacturer's instructions.
  2. Read MSDS sheets and follow requirements.
  3. Wear clothing adequate to protect against skin contact and irritation.
  4. Wear a respiratory mask.
  5. Do not cover or pack insulation around bare stovepipes, flues, electrical fixtures, motors or any heat-producing equipment such as recessed lighting fixtures because trapped heat and blocked air circulation can create safety problems ("IC" rated recessed lighting fixtures can be insulated). Air leaks around flues and chimneys SHOULD be sealed using fire-resistant materials such as sheet metal and high temperature caulk.
  6. Do not cover attic vents with insulation. Proper ventilation in attics helps prevent overheating in summer and moisture buildup all year long.
  7. Have a professional make sure all combustion appliances are operating properly.
  8. If your house was insulated with vermiculite insulation it could contain asbestos. Take special precautions if your home has vermiculite insulation.

Materials and Equipment

  1. Caulk: Seals gaps of less than 12", select grade (interior, exterior, high temperature) based on application
  2. Spray foam: Fills large cracks and small holes. Consider new latex-based foams. Do not usenear flammable applications (e.g., flue vents). Do not use expanding types on windows and doors.
  3. Backer rod: Closed-cell foam or rope caulk. Press into crack gap with screwdriver or putty knife. Often used with caulk around window and door rough openings.
  4. Gaskets: Apply under the bottom plate before an exterior wall is raised or use to seal drywall to framing instead of caulk or adhesive.
  5. Housewrap: Installed over exterior sheathing. Must be sealed with housewrap tape or caulk to form an airtight seal. It resists water but is not a vapor barrier.
  6. Sheet goods (plywood, drywall, rigid foam insulation): These materials form the air barrier. Air leaks only at unsealed seams or penetrations.
  7. Sheet metal: Used with high-temperature caulk for sealing high-temperature components, such as flues and chimneys, to framing.
  8. Polyethylene plastic: inexpensive material for air sealing, also stops vapor diffusion. All edges and penetrations must be completely sealed for an effective air barrier.
  9. Weather-stripping: Used to seal moveable components, such as doors, windows, and attic accesses.
  10. Mastic: Seals air handlers and all duct connections and joints.
  11. Rigid Foam Insulation: Used on exterior and interior walls; serves as sheathing.

Inspect windows and doors for air leaks. See if you can rattle them, since movement means possible air leaks. If you can see daylight around door and window frames, then the door or window leaks. You can usually seal these leaks by caulking or weather stripping them. Check the storm windows to see if they fit and are not broken.

Do-it-yourself Home Sealing, Energy Star

Insulation Fact Sheet, Department of Energy