Question of the Day - #84 - “air seal” like an “air guitar?

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Question of the Day - #84 - “air seal” like an “air guitar?

Postby RDavidson » Sun Nov 30, 2014 1:35 pm

2015 MN Rules 1322.0402, subpart 2, R402.1.1.7, provides prescriptive requirements for use of fiberglass insulation on the interior of a basement walls. One of the requirements for use of this product is that “The top and bottom plates shall be air sealed to the foundation wall surface and the basement floor”. What does “air sealed” mean? Do they mean caulked? Why didn’t “they” say that?

It says the plates must be “air sealed” to the “foundation wall surface”.

R402.1.1.4, #2, provides general requirements for all interior foundation insulation requirements and says “if a frame wall is installed, it shall not be in direct contact with the foundation wall”. Combining the requirement for an “air seal” and “no direct contact”, what would you expect to see?

Most homes are built with a foundation sill that is 1 ½ inches thick. The floor system sits on the sill. When you construct an interior non-bearing perimeter wall, the bottom of the top plate is usually level with the top of the foundation wall (corner to corner). How do you “air seal” this interface? Could you attach a brush type piece of weather stripping? In the real world, it is very unlikely that the foundation is so straight, plumb, and level that you can construct a wood frame wall that is not in contact with the foundation yet results in the top plate being close enough to the foundation wall that you can “air seal” the joint. Is this requirement achievable?
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