In my previous post on older homes, I explained the importance of controlling bulk water and vapor before tackling energy-performance upgrades. In this post, I’ll talk about air leaks. Air movement can affect both the wetting and drying potential of a material; air moving in and out of a building also influences energy usage and can impact indoor air quality (IAQ).
Air-sealing is a big deal in the building science community. Codes now require blower-door testing in new construction with air-sealing mandates at 3 or 5 air changes per hour at a test pressure of 50 Pascals, depending on location. Blower-door testing of older homes is done for different reasons. I test them as part of an energy audit, and I recommend testing if any changes to the building shell are planned. Something I learned the hard way: Replacing a few windows can change a building’s airtightness, which can affect other conditions in the building. Using a blower door to find and seal air leaks is critical if the goal is to decrease energy usage and increase comfort. The locations of holes and the natural ventilation rate will be unique to each home.
Start in the attic
In a cold climate like mine, I start by looking for air leaks in the attic. Vented, unconditioned attics are common in my market, and air-sealing wasn’t a consideration when these older homes were being built. Usually, sealing the attic presents the best envelope performance–improvement opportunities. (It should always be done before additional insulation is installed. It may even be necessary to remove existing insulation to expose potential problem areas.)
There are a few different strategies for air-sealing an attic. Generally, the approach depends on how the attic is constructed. There are several good articles on GBA covering this topic. Rather than…