Increasingly stringent code requirements on air changes per hour, along with demand from today’s home buyers for energy-efficient housing, makes it critical for builders to achieve certain metrics for airtightness in their homes. In addition to reducing electric bills, an airtight home can provide a more comfortable, durable residence that has fewer opportunities for moisture and mold buildup. Improved indoor air quality might interest current and prospective home buyers who have spent a lot of time at home during the pandemic.
Before considering strategies to implement, builders need to locate where exactly in the house the air is leaking.
Performing a blower door test will help determine how much air per hour is exchanging between the interior and exterior of the house. Using tools such as an infrared camera, a smoke machine to physically see where the air is circulating, or even using your hand to feel where air is flowing in and out can help determine where there are unwanted air leaks. Use these tools around weak points where joints meet — such as where holes are cut for electrical outlets or plumbing fixtures, and between conditioned and unconditioned spaces such as the garage — to get a better sense of where small changes to cracks and gaps might make a big difference in the home’s overall airtightness.
Strategies to improve unwanted air filtration can vary depending on the location of the project and how certain materials perform in various climate zones, but consider trying different combinations of the following tactics to see what works best for your project:
- Create redundancy in connection points. For instance, use the correct type of tape where different layers such as the water-resistive barrier (WRB) and the oriented strand board (OSB) overlap or meet.
- Utilize products that can help plug small holes and cracks. The technology works by using a sticky particle sealant, which travels with air and plugs spaces as the air travels through the house.
- Apply a caulk or a sealant with properties that allow it to stick to a range of materials. This can be helpful to put between the concrete slab and interior wall. (Be sure to check the recommended temperature for application in certain cold climates.)
- Install a polyethylene gasket material. It has a relatively straightforward application; by stapling it directly to the wood framing, it can enhance the role of the drywall as an air barrier.
- Seal with a foam-based drywall gasket that gets applied pre-drywall. It adheres directly to wood framing and once cured, the drywall can be installed directly over it.
- Consider buying gasketed outlets, which come with a flange and a mechanical seal already on the box, so that the gap between the outlet box and drywall decreases.
- Explore structural insulated panels (SIPs), which come with insulation and already have OSB on both sides. Building with SIPs is one alternative to building with lumber; with fewer connection points, it can act as a more continuous insulation.
- Apply spray foam. It is yet another option for sealing locations where there are connection points.
- Use caulks, tapes and foams in other weak points, such as around plumbing penetrations, recessed lighting and outlet boxes.
There is no silver bullet for getting a house perfectly airtight, but paying detailed attention to connection points throughout the building process can make a big difference in decreasing the number of cracks and gaps through which air can travel.
Be sure to pair an airtight building envelope with mechanical ventilation to bring in fresh air as well.
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