Using Interior Poly As an Air Barrier
Alaskan builders still use a technique developed in the 1980s by Canadian superinsulation pioneers: the use of interior polyethylene as an air barrier
Back in the 1980s, Canadian energy experts urged builders to use interior polyethylene as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. material. If the poly was installed conscientiously, and all seams were sealed with Tremco acoustical sealant, the approach worked well — at least in cold climates.
When the same techniques were later adopted by American builders in places like Ohio and North Carolina, builders learned an important lesson: "Climate matters." In hot climates or mixed climates where air conditioning is common, interior poly can become a condensing surface for exterior moisture during the summer. In many cases, the result was mold and rot.
These days, interior polyethylene is not recommended in most U.S. climates, especially in any home that may be air conditioned during the summer.
Alaskan builders still use interior polyethylene
But what if you are building in Alaska or northern Canada? Well, in those climates, interior polyethylene still makes sense. That's why the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska, recommends that Alaskan builders use interior polyethylene as an air barrier.
The CCHRC has produced an excellent video on this topic. In the video, Ilya Benesch, a building educator at the CCHRC, explains how to do a good job of air sealing with interior poly. If you are building in northern Canada or Alaska, the techniques shown in this video (below) are worth emulating.
For more excellent advice on building techniques for very cold climates, visit the CCHRC website.
[Author's postscript: in July 2012, when I was vacationing with my family in Alaska, we all showed up unannounced at the Cold Climate Housing Research Center in Fairbanks, where we were warmly greeted by Jack Hébert and Ilya Benesch. Not only did Jack and Ilya give us a tour of the CCHCR facilities, they let us use the building's showers — a generous gesture in a city where many buildings, including the one where we were staying, lack running water. I'd like to thank Jack and Ilya for their hospitality as well as their building science research.]
- Colc Climate Housing Research Center
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