Air-sealing a brick house
I live in a 4-story, 5,000-square-foot, balloon-framed, brick house built in the 1920s or so.
I recently did a pressurization blower-door test on the house and it only reached 20 Pa or so, but I identified some huge places where air is leaking, including the basement ceiling which is open to the floor cavity and 2 closets on the third floor which connect to the attic/outside somehow.
I was about to seal these places up when someone who has a lot of experience with residential energy efficiency told me that because it’s a brick house and therefore has air-tight walls, it would be more worth my time to explore penetrations through the building envelope from the outside.
Is this true? Is the approach to air-sealing brick houses different from sealing houses with typical siding? I don’t know what kinds of penetrations would be obvious from the outside besides doors and windows. Would it be helpful to run a pressurization blower-door test again and look for leaks from the outside?
Thanks!
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Replies
Karen,
I think you have the right idea. If you have identified big air leaks in your basement and top-floor ceiling, then by all means seal them up. That's where most air-sealing contractors start: the basement and the attic. Sealing those leaks goes a long way towards addressing stack-effect leakage.
I'm not sure what your friend was thinking, but if you can see any penetrations in the brick walls of your home that require air sealing, it can't hurt to seal them. Just don't seal up the weep holes at the bottom of your walls, if any!
Karen,
Seal the tops and bottoms of balloon walls for the most measurable reduction in air infiltration....especially if the top side of the walls communicates with a vented attic. You should air seal the entire attic plane thoroughly. I don't get what the "brick guy" was talking about....air sealing is always prioritized at the top of the home (and attached garage....but for CO reasons).
Yours is a big, old home. My experience is that big old homes often had a few additions or alterations performed through the years. Areas where additions or renovations connect are notoriously leaky. Often, a balloon framed wall that was originally an end wall of the home becomes a "normal" looking interior partition wall after an addition, but this balloon wall in the middle of the home acts as a chase for convection. Use an infrared with the blower door on a cold day. You see air leakage at some funny spots....."There is 30 degree air coming out of the recessed lights of my first floor kitchen? Really???"
I always find that the bottom side of the balloon wall is tricky. Use a plug (a rolled up fiberglass batt works) shoved into the cavity from the basement, and then seal with closed cell spray foam.
good link: http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist/?searchterm=critical%20seal
There is a very good chance your big boiler (5000' house!) is drawing its combustion air from these wide open exterior walls. It is imperative to perform a combustion analysis and draft test on the boiler and any other combustion appliances after you air seal.