We get asked a lot what the biggest difference is between the 100K House project and the Passive Project. The answer is always the same. Air Sealing.
On a Passive House, we have to hit a very strict target on our blower door test of 0.6 Air Changes per Hour at 50 Pascals of pressure. This is no easy task. Every single seam must be caulked, or preferably taped, to hit this target. That all starts with the foundation. We’ll review a couple of the key details for the foundation air sealing below.
The basic concept is that we have to have a continuous air barrier around the entire home starting with the foundation. Last time we installed an air barrier, but did not bother too much with seams. This time we have to tape every seam with Tyvek Tape. The yellow poly you see is actually 15 mils thick to help prevent puncturing while we work on it.
The next thing to worry about is every electrical or plumbing penetration through the air barrier. You can see above that we eliminated the need to worry about our electrical penetrations in the image above by placing them in the concrete and above the poly.
The plumbing penetrations require a much more more thorough detail. We must encase every penetration through the air barrier and slab in PVC that is roughly 2″ larger in diameter than the penetration. After that is done, the poly air barrier is securely taped to the outside of the PVC. Once we have poured the slab, we then fill the inside of the PVC with spray foam. Any cracks that we don’t like are then sealed with caulk. The detail can be shown in the diagram below. Basically the poly is the air barrier until it reaches the penetration. Then the assembly shown must become the air barrier.
Last but not least, we must wrap the poly up around the edges of the slab like shown below. You can also see the construction details in the previous post on slab insulation. When we set the SIPs walls, we will tape this poly to the inside layer of OSB on the SIPs that will then take over as our air barrier for the rest of the homes.
Questions, comments? This was a lot of work and coordination. If you look closely, you’ll even see our GC in the pics actually taping seams. The dedication. The commitment to extreme Passivity in home building. Fantastic.
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