Best Practices
Monday, September 26, 2011

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Air-Sealing Best Practices

Opening the walls, floors or ceilings of an older home? Working in its basement, attic or crawlspace? Replacing windows or doors? Cutting holes? Installing can lights? Adding on? Air-seal where possible, and with care.

In the seventh of his “7 reasons not to skip the air-sealing,” home-performance expert Alllison Bailes advised remodelers to take every opportunity for some of the lowest-cost, highest-return home improvements that can be made. From Bailes’ July 18 blog post on the Energy Vanguard blog:
"Those walls, floors, and ceilings may not have been open for decades, and when you're done, they'll be closed up for decades again. Don't miss this opportunity. If you're already in there doing remodeling work, take full advantage. You'll be rewarded with a house that's more comfortable, durable, healthful, and efficient if you do it properly."
In anticipation of the cold weather ahead, here’s a brief overview of some commonly overlooked air-sealing best practices for remodelers. Click on the links to learn much, much more.
  • Understand the benefits of air-sealing old homes -- and the need to do so. Start here with Bailes’ “7 reasons.” 
  • Before insulating existing walls, “strip them from the outside and confirm that everything is properly flashed and shingle-lapped to keep water out.” That’s a comment from “Green Curmudgeon Carl Seville, in a comment on Bailes’ blog post. 
The issue, Seville wrote, is the potential risk of moisture in old walls. “If you insulate an existing wall that doesn't have a complete moisture barrier and well flashed windows (and what existing wall does?), then you are likely going to get bulk water into the wall cavity, and the insulation will keep it in there, likely causing mold and rot.”
  • Get rid of the big holes. You don’t need a blower-door test to find them. In Just Right and Airtight, Joe Lstiburek of Building Science Corp. compiled the following list of “big holes”: 
“Bathtubs on exterior walls, fireplaces and chimneys on exterior walls, garages attached to houses with bedrooms over them, cantilevered second floors, interior soffits dead ending into exterior walls and dropped ceilings under attic insulation. Done. Make these go away with draftstopping and, presto, the comfort problems ... go away.”
  • Don’t rely entirely on the blower-door test. As a prelude to the bullet-point above, Lstiburek wrote this:
"Folks are building houses and retrofitting existing houses with increased airtightness, and this is great. They use a blower door to help measure leakage, and this is also great. But then they think that a blower door actually is a precise measuring tool for how air will leak across the building during service. Wrong. Even more serious an issue is to then take the leap that using a wrong assumption about the results of an approximate measurement can be used to decide that mechanical ventilation is not needed. Bad, very bad, and potentially deadly.... A blower door measures a characteristic of the house, not the leakage rate of the house in service."
  • Keep up with new products. It’s not easy, given the rush of new product developments, but sources such as Martin Holladay’s Musings of an Energy Nerd blog provide ongoing coverage of significant manufacturer developments that can make buildings at once more airtight and well-ventilated. Check out last week’s post about “sprayable caulks” from Owens Corning and Knaupf.
Some more air-sealing resources:

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