Conditioned Crawl Space
CurtisLee
| Posted in GBA Pro Help on
I am building a conditioned crawl space in the mixed climate of western Washington State and the design for my floor system is TJIs over pony walls. I want to totally encapsulate the crawl space from plate to plate with 3 in spray foam on stem walls and 2 in spray foam over drain rocked dirt.
My question is about the interior pony walls carrying the TJIs.
Pony walls are 2×4 on 2×4 PT plate. IF THE 2 IN CLOSED CELL SPRAY FOAM ENCAPSULATES THE BOTTOM 2 IN OF PONY WALL STUDS WILL THEY ROT?
Thanks
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Replies
It sounds like you are building a permanent wood foundation? I would absolutely NOT insulate that with spray foam. I would absolutely NOT build such a foundation myself, either -- use concrete here. No matter what you do, a wood foundation will never have the longevity of concrete, and if the foundation fails, so does the rest of the house. Foundation repairs are very expensive too!
Bill
I was not clear and assumed it was understood that stem walls are reinforced concrete.
So whats your opinion on my rot question?
Malcolm already go most of it covered. I would recommend using something more robust than sill sealer for a capillary break. I recommend EPDM sheet in this case. If you can limit the amount of moisture that can get to the framing, you have much less to be worried about in terms of drying. Using a reliable capillary break helps to avoid issues with the mudsill sitting in damp.
Bill
The pony walls need to have some sort of foundation under them if they're load bearing. I would do a trench of concrete and have it extend six inches or so above grade. The sole plate of the pony wall needs to be treated and there needs to be a capillary break between the wood and concrete.
If done this way the foam should end well below the wood.
Yes, I have the interior concrete footings in place and yes there will be a capillary break under the PT plate.
See attached please for assurance that we understand each other,
thanks
Curtis,
You are fine. If the bottom plates do see a small amount of moisture they can dry to the inside.
Two unrelated things you probably have already thought of:
- Unless the TJs line up with the studs below, you probably need a second top-plate on the pony walls.
- You don't show a rim-joist on the TJs. The sub-floor extending out to the sill-plate may be enough, but it is something to look into.
You can also extend the sill plate a bit in and use top mount joist hangers for the I-joist. This way you don't have to build a pony wall and still have a bit of room between the i-joists and concrete for insulation.
I would not bother with spray foam here. Simple rigid foam glued to the foundation and along the floor works just as well. You would need poly for the a rigid install along the crawl floor.