Air-Sealing your Home
Wow, the revelation that Ultrafine Particles (UFPs) from outdoor pollution can easily penetrate a home’s interior through cracks and leaks has really stirred our thinking. Specifically, a 2018 study on UFPs from airport traffic during prevailing winds caused indoor pollutants to rise by 1.7 fold (170%), and HEPA filtration inside the homes only lowered them by 33%. What does this mean? Our homes are leaky, and no amount of indoor air filtration can keep up when outdoor pollutants are raging! This could be wildfires, oil refineries, a major highway, a major port, or any heavy industry or power plant. Basically, the only way to keep outdoor pollutants outside is to either seal the building envelope better, or use a positive pressure system where the inside of the building stays pressurized, so that airflow is always inside to outside.
Before we get into the specifics, home builders in the past usually only concerned themselves with one barrier, a vapor barrier. This was the felt paper, housewrap or other system installed under the cladding that prevented rain and moisture from entering the building. A vapor barrier is not the same as an air barrier, and air barriers are much less common in residential and even commercial construction. We’re talking about air barriers in this post, as air barriers are one way to block UFPs from entering your home.
Here are some options for making an air barrier (sealing the building envelope):
From the outside: this is best accomplished during construction or major renovation:
Applying a membrane air barrier like Delta Vent SA over sheathing involves primer, tape and the barrier; this video shows how it is installed and the tape is preferred to caulking in preventing air leaks.
From the inside: there are 3 ways to seal the inside: Before drywall, using the drywall itself as an air barrier, and after drywall.
Use a product like Knauf Insulation EcoSeal, a waterbased elastomeric sealant. First the exterior sheathing is installed and taped. Then the sealant is applied to all interior seams and cracks with an airless sprayer at 1700 to 2200 psi, which really forces the sealant into any cracks. It fills gaps from 1/16” to ⅜”. Here is a description of how it’s installed.
OwensCorning EnergyComplete is a two part insulation and air-sealing system. First a latex sealant is sprayed on the interior of sheathing (like Knauf Insulation Ecoseal), then the wall cavities are filled with either blown-in insulation (by using netting to retain the insulation) or with spray foam.
You can apply an air barrier like Intello Plus (ceiling video, wall video, penetrations video) on the underside of ceiling joists, all along walls, sealing it to the subfloor. Again, run a blower door test before installing drywall so that large leaks can be corrected.
Use spray foam: spray foam is seen as a one stop shop that insulates AND seals, but it requires careful installation and checking through a blower-door test. This article shows how an older house that is renovated with sprayfoam insulation can be surprisingly leaky. The application of the foam is incredibly important in creating the seal, as small gaps between the spray foam and the back of the drywall can make a highway between penetrations. The air barrier needs to be tested before the drywall is installed so that foam imperfections can be corrected.
Use AeroBarrier: This is a waterborne acrylic sealant that is sprayed into a pressurized space, using the pressure to guide the sealant into any cracks or crevices. The process can be applied pre- or post-drywall with any type of insulation.
Using drywall: if you skip an air barrier membrane, you can use the drywall itself to make an air barrier. The most problematic areas are the joints and penetrations, which can be addressed using the right materials. You’ll need special electrical boxes, gasket material, expanding foam, flexible caulk and adhesive; here are 2 articles on what to consider and how to hang airtight drywall.
After drywall: it’s not ideal, but you can still make major sealing improvements after your home is “finished”. Start by doing a visual check for daylight or artificial lights around the door and window perimeters when they are closed. You can use your hand or a candle to find air leaks and drafts as well. Check under sinks and behind appliances like refrigerators and gas stoves for wall penetrations that have not been sealed. Once you’ve sealed as much as you can with foam (be careful using expanding foam), caulk, and weatherstripping, call in an energy auditor to do a “blower door test” to see what you may be missing. They should be able to tell you how leaky the home is in terms of “Air Changes per Hour” (ACH), and suggest and/or perform other remedies to lower the ACH, making the home tighter.
Because of the continued increase in interest for air-sealing homes and businesses, there is an Air Barrier Association of America (abaa.org). The association is “committed to educating the public about air barrier systems and developing a professional air barrier specialty trade and industry dedicated to the installation of effective air barrier systems in buildings on a nationwide scale.” Here are some of the resources they have: