Improving the Building Shell with Air Sealing (Part 2 Home Energy)
All homes have an air barrier, but some are, of course, better than others. Look around your home, whatever materials you have on your home to stop air from getting in a getting out is part of your air barrier. This varies greatly from drywall to glass. An air barrier helps to reduce the amount of conditioned air that is lost and replaced by unconditioned air. The faster a building exchanges air with the outside, the more energy is needed to maintain the structure at a comfortable temperature. There are always holes in your air barrier, because otherwise you would suffocate in your home. The trick is to keep the number of holes to an acceptable level without compromising safe and healthy ventilation.
Energy auditors use a blower door, which is essentially a door frame, tarp, and fan that goes in an exterior door, hooked up to a pressure manometer. Basically, this test tells the CFM leakage of the structure at 50 pascals of pressure. While the fan is running, the auditor can typically find leaks using various techniques and equipment. Based on the structure, the leakage number, and the subsequent tests, they then determine if it is safe to seal up the house further, where to seal, and what potential savings are to be gained.
It is not recommended to perform air sealing on a house without having a blower door test done by a BPI certified Building Analyst. For example, maybe your house is right on the border of allowing mold to develop. You proceed to seal the house too tight, and mold begins to develop in the bathrooms or kitchen. Perhaps you have many pets and odors that are tolerable with your leaky house when they are quickly exchanging with the fresh outdoor air, but then you seal the house up to a point where the smells become unbearable. Or you might encounter the biggest fear of any building analyst, the possibility of a backdrafting flue causing carbon monoxide poisoning.
Older homes tend to be leakier than new homes. Air sealing in the attic is typically the best place to start. Recessed lights, plumbing chases, wire intrusions, open wall cavities, and attic hatches are common leakage points. If you are sealing a recessed light, make sure you follow local fire code.
If you would like to learn more about specific air sealing techniques, the Department of Energy link below has some good information. DOE Air Sealing link.
In my experience of going through homes, I was surprised by how poorly homes were constructed where it was out of sight of the homeowner. What you could see looked nice, but up in the attic, and sometimes in the basement I could really see some shoddy construction. Below are some pictures from a few of my jobs showing common leakage points and poor construction.
***Incidentally, a targeted air sealing job done by a professional BPI Building Analyst can be a great investment. You will improve the comfort of your home and save enough on your utility bills to pay for the job over time. Below is the average return on investment that I saw amongst the homes I worked on.
ROI on Air Sealing – AVG 18% (It really varies on the structure, energy prices, how difficult the air sealing techniques are, and how good your contractor is at finding and sealing the biggest leaks. The materials are usually inexpensive, but can use a lot of labor)