Air leakage, or infiltration, occurs when outside air enters a house uncontrollably through cracks and openings. Properly air sealing such cracks and openings in your home can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment.
It is unwise to rely on air leakage for ventilation because it can't be controlled. During cold or windy weather, too much air may enter the house. When it's warmer and less windy, not enough air may enter. Air infiltration also can contribute to problems with moisture control. Moldy and dusty air can enter a leaky house through such areas as attics or foundations. This air in the house could cause health problems.
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.
Air Sealing an Existing Home
Air sealing is one of the most significant energy efficiency improvements you can make to your home. Air sealing will not just reduce energy costs; it will also improve your home's comfort and durability.
Detecting Air Leaks
You may already know where some air leakage occurs in your home, such as an under-the-door draft, but you'll need to find the less obvious gaps to properly air seal your home.
For a thorough and accurate measurement of air leakage in your home, hire a qualified technician to conduct an energy audit, particularly a blower door test. A blower door test, which depressurizes a home, can reveal the location of many leaks. A complete energy audit will also help determine areas in your home that need more insulation.
Without a blower door test, there are ways to find some air leaks yourself. First, look at areas where different materials meet, such as between brick and wood siding, between foundation and walls, and between the chimney and siding. Also inspect around the following areas for any cracks and gaps that could cause air leaks:
- Door and window frames
- Mail chutes
- Electrical and gas service entrances
- Cable TV and phone lines
- Outdoor water faucets
- Where dryer vents pass through walls
- Bricks, siding, stucco, and foundation
- Air conditioners
- Vents and fans.
You can also try these steps to depressurize your home to help detect leaks:
- Turn off your furnace on a cool, very windy day.
- Shut all windows and doors.
- Turn on all exhaust fans that blow air outside, such as bathroom fans or stove vents.
- Light an incense stick and pass it around the edges of common leak sites. Wherever the smoke is sucked out of or blown into the room, there's a draft.
If you don't want to turn off your furnace, you can just turn on all your exhaust fans to depressurize your home.
Other air-leak detection methods include the following:
- Shining flashlight at night over all potential gaps while a partner observes the house from outside. Large cracks will show up as rays of light. However, this is not a good way to detect small cracks.
- Shutting a door or window on a piece of paper. If you can pull the paper out without tearing it, you're losing energy.
Note that air sealing alone can't replace the need for proper insulation throughout your home, which is needed to reduce heat flow.
Once you have identified all your air leaks, you can then apply air sealing techniques and materials as needed, including caulking and weatherstripping.
Air Sealing for New Home Construction
Air sealing is an important factor when constructing an energy-efficient home.
Air barriers block random air movement through building cavities. As a result, they help prevent air leakage in your home, which can account for 30% or more of a home's heating and cooling costs. Air barriers also help control moisture in a home. While they stop most air movement, air barriers also allow any water vapor that does enter to diffuse back out again.
Types of Air Barriers
Many of the materials used in a house for structural purposes and finished surfaces also act as air barriers. For many homes, these materials include the following sheet goods that form the ceilings, walls, and floors:
The most common air barrier material is house wrap. House wraps are usually wrapped around the exterior of a house during construction. Some wraps have better weathering or water-repelling abilities than others. All come in a variety of sizes for different purposes. Wraps usually consist of fibrous spun polyolefin plastic, which is matted into sheets and rolled up for shipping. House wraps may also have other materials woven or bonded to them to help resist tearing.
In wet climates, house wrap sometimes reacts poorly with certain kinds of wood siding. Lignin (a naturally occurring substance in many species of wood) is water soluble and acts as a detergent. Like all detergents, it decreases surface tension and destroys the house wrap's ability to repel water. Field research has shown that wood lignin makes it easier for liquid water to pass into the wall. Certain types of wood siding, such as redwood, cedar, and manufactured hardboard siding, seem to accelerate the problem. To avoid this problem, carefully attach heavy building paper (30-pound asphalt impregnated) to the walls as a substitute for house wrap. You also might install felt paper over the house wrap as a water-repellent surface.
Some types of insulation—such as foam board and dense-packed cellulose insulation—can be effective at reducing air flow as well as heat flow. However, the most common type of insulation—fiberglass—does not stop air leakage. In older homes, dirty fiberglass insulation is a telltale sign of air movement (it collects dirt like a filter).
The type of air barrier to choose and how to use it depends mainly on where you build a house and the climate. In a southern humid climate, you might also consider using a combination air barrier/vapor diffusion retarder.
Continuous Air Barrier
To create a continuous air barrier throughout your home for maximum energy efficiency, you need to seal all the holes and seams between any sheet goods with durable caulk, gaskets, and/or foam sealants.
If you use a house wrap, sealing all of its joints with "house wrap tape" is a good practice that improves the wrap's performance about 20%. All house wrap manufacturers have a special tape for this purpose.
You also might consider using the Airtight Drywall or Simple Caulk and Seal wall construction technique to create a continuous air barrier.
Airtight Drywall, and Simple Caulk and Seal
Two wall-construction techniques—the Airtight Drywall Approach and Simple Caulk and Seal—can be used to create a continuous air barrier within a house. Using one of these techniques can significantly reduce air leakage to help improve a home's energy efficiency.
Both the Airtight Drywall Approach (ADA) and Simple Caulk and Seal (SCS) create an effective airtight wall by sealing the drywall to the building structure. To create a continuous air barrier, the exterior sheathing and interior wall finish are sealed to the framing.
The exterior sheathing can be sealed using a variety of methods; caulking the seams of the plywood (or the foam board insulation) is one way. More common is the use of a house wrap or a special tape made specifically for house sheathing. Depending on the climate, additional water vapor control may also be needed. These vapor-control materials often include polyethylene plastic sheeting, faced fiberglass insulation, foil-backed wallboard, or an interior "vapor barrier" paint.
The main difference between the ADA and SCS methods is that with the SCS, seams and gaps are sealed after the exterior sheathing and drywall have been installed and finished. With the ADA, sealing is carried out during the entire construction process.
The typical procedure for ADA is to seal any seams and joints where the foundation, sill plate, floor joist header, and sub-floor meet. The spaces between floors, the sub-floor, rim joist, and plates are also sealed. The wall-framing plates are sealed to the lower sub-floor and the upper rim joist. Gaskets are often used at the top and bottom wall plates (between the drywall and framing) and between ceiling drywall and attic joists. Airtight electrical boxes (or standard electrical boxes sealed with caulk) complete the air barrier. Holes where pipes and cables pass through also need to be sealed before the wall and ceiling finishes are applied. After all this has been done and the perimeter drywall seams have been finished, the room is effectively sealed from expensive and uncomfortable drafts.
In some ways, the SCS method is superior to the ADA. The SCS is less disruptive to construction workers, which can speed up the construction process. Sealing after the drywall is finished also provides a drier work environment while sealing. A dry environment can help ensure that the sealing job performs well, since most caulks don't stick to wet surfaces. However, the SCS is less comprehensive than the ADA. The SCS may miss some critical points inside building cavities that become inaccessible after the wall board is installed.
Tests done on both ADA- and SCS-detailed homes indicate that both resulted in similar energy savings. After a year of monitoring, one study found that the ADA house had 0.67–1.80 air changes per hour (ACH) at 50 Pascals pressure. An identical conventional home without ADA had a 2.23–2.59 ACH at 50 Pascals. [Fifty Pascals of pressure imitates a 20-mile-per-hour (32-kilometer-per-hour) wind striking the building from all sides at the same time.]
Such airtight homes often consume one-third less energy when compared to similar unsealed homes. Also, test measurements of airborne contaminants in an ADA- or SCS-detailed building (including those with mechanical ventilation) found that the reduction of air infiltration did not diminish the indoor air quality significantly. However, for health and safety, it is strongly recommended that a Heat Recovery Ventilator (HRV) or Enthalpy Recovery Ventilators (ERV) be installed in an airtight home for proper ventilation.