by John H. Cluver, AIA, LEED
For years, people have been talking about the importance of insulation to reduce energy loss, but the Department of Energy has determined that up to 40% of a home’s heat loss can be attributed to infiltration. Fortunately, home energy audits, particularly those using blower door tests, can be very helpful in identifying areas of infiltration, and in many cases the process of sealing those leaks is easy and affordable.
Some of the most common areas of infiltration can be found at:
• Doors and windows. There are a lot of joints here, where the moving door or sash meets the frame, and where the frame and trim meets the wall. A typical door with a tiny gap of 1/32” at its perimeter is the equivalent of having a standard window open ¼”. Make sure the wall connections are tightly sealed. Add weatherstripping at the movable parts. Bent metal works great at doors, and metal channels are the best on wood double hung windows, but other, cheaper options also exist which can also be quite valuable.
• Electrical outlets. Especially at houses that lack insulation, outlets and light switches in exterior walls provide a route for infiltration. On windy days in particular, you can feel the pressurized air being forced through these openings in the wall. A simple solution is to get foam inserts which go behind the cover plates. A more involved solution would be to insulate the wall cavity, but that carries with it issues of its own—which we can get into another time.
• Foundations. Another possible location for many gaps is the intersection where the exterior walls meet the foundation—particularly that of a wood framed building. Some caulk or foam sealant and the ability to fit your hands into tight and awkward spaces can help greatly in these locations.
• Chimneys. A fireplace chimney is designed to quickly ventilate hot air from a house, whether or not there is a fire in it! Always make sure the flue is closed when it is not in use, and if the fireplace has doors, keep them closed as well (added bonus: both of these measures are also extremely helpful should you be as unlucky as I was to have a squirrel fall down your chimney).
• Attic hatches. Make sure openings into the attic are tight and, if possible, insulated. Heat rises, and a properly sealed, insulated, and ventilated attic will be almost as cold as the outside air.
A logical conclusion from all of this would be: the tighter (or less infiltrated) we can make a building, the better. Unfortunately, that isn’t always the case. Because our buildings (and the people living and working within them) require a certain amount of fresh air, if a building is too tight, the air gets stale with carbon dioxide and other gasses put off by people and objects. Humidity levels can increase, creating a wonderful environment for the growth of mold (I witnessed this first-hand in New Orleans six months after the devastation brought by Hurricane Katrina; houses that were boarded up tight had some of the most spectacular mold growth I have ever seen). Water that gets stuck behind a cladding material needs to be able to dry or wood and steel could rot and rust. Boilers, furnaces, fireplaces and other combustion devices also need fresh air. In a newer building that has a tight design, it is possible to address these issues and to have mechanical systems that efficiently provide the necessary fresh air. Older buildings, however, do not always have this advantage and in fact always relied on (or at least benefitted from) a certain level of porosity in their exterior envelope.
Does this mean that we shouldn’t be taking measures to plug the gaps that we find and lower the infiltration levels of a building? Absolutely not. Many older buildings have much more infiltration than they need. To put it in perspective, a well-sealed new home could provide roughly 0.5 air changes per hour (ACH) or less, which is getting close to the point of being too tight. In contrast, an older home in good condition provides double this amount at 1.0 ACH, whereas a drafty house lacking weather stripping and caulking can be closer to 4.0 ACH. If a house with a 4.0 ACH is losing 40% of its heat to infiltration, sealing those gaps to bring it closer to 1.0 ACH could save hundreds of dollars or more every year. As you can see, there are simple, cost-effective ways to stop drafts and heat loss and minimize the amount of infiltration of a building, especially at areas such as windows where the effect is directly felt by occupants. But when doing so, just remember that when it comes to stopping infiltration, it is possible to have too much of a good thing.
Posted in Sustainability