What to do with SIP face exposed below siding?
We are building our first SIP house complete with SIP foundation. We will be using Hardiplank siding which requires 6″ clearance between the lowest plank and grade.
So for those 6″ or so the skin of the panels will be exposed, and in certain areas it may not be the foundation panels which will have the pressure treated plywood, etc.
So this general question is: What should I do with that space? Normally this space is just exposed poured concrete walls, but with a SIP building, what do you do?
I’ve heard just put treated ply over it (ugly), fiberglass board (what? where do i get that?) more cement board (the problem i see there is that we are already using cement board which isn’t supposed to be touching grade)
Any help or experience would be appreciated.
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Replies
Joe,
The best solution is stucco.
Kevin,
I have never heard of anyone using OSB-faced SIPs for a foundation wall. Frankly, that's scary.
Here are links to two manufacturers of SIPs for foundations. Both manufacturers face their panels with treated plywood, not OSB.
http://www.extremepanel.com/sipsproducts_sipsfloorsfoundations.shtml
http://www.thermapan.com/
How long can a buried SIPS panel possibly last, no matter what you do to try to waterproof it? 30-40 years? At that point, the whole thing starts sinking into the ground??
Cementitous stucco on chicken wire over two layers of tarpaper over a SIP will fail at grade.
The building dept. made me put bituthane over the OSB SIP from the top of the foundation up 12". Then sheet metal over that before putting on the stucco. Also don't pour a sidewalk against the stucco without a spacer.
That assembly has held up well for 10 years so far.
Martin and David,
I reworded my answer above so it would be harder to misunderstand.
The takeaway is that the foundation, whether it's concrete or a foundation SIP, should project at least 6"-8" above grade. Then you can use stucco.
Stucco over OSB within 6" of grade will eventually rot the OSB.
Kevin,
There are two different issues here.
Issue #1 is the need for a foundation to extend at least 6 inches above grade. This code requirement can be found in the 2006 IRC section R404.1.6. If an above-grade SIP with OSB facing is installed less than 6 inches above grade, that is a code violation and the OSB is likely to rot -- whether or not you use stucco for your siding material.
Issue #2 is the question of the best way to finish the pressure-treated plywood facing of a foundation SIP. My assumption is that such a foundation would extend at least 6 inches above grade, like any foundation, although I am not sure whether the code is explicit on this question.