Sheathing flush with foundation or overlap?
Hi guys, I’m finally going to begin building next week. I am not a builder, so I apologize for the ignorance. I will have 2×6 sheathed walls with 3″ insulation, rainscreen, james hardie board.
I have 3″ foam around the foundation of the house. to continue this over the sheathing, I’d like to know if it’s acceptable to butt the end of the sheathing to the top of the foundation? I would then use Prosoco to fill and seal the joint where the bottom of the sheating sits on the top of the foundation wall.
It seems that most builders bring the sheathing down a few inches over the outside of the foundation wall. Is there any harm in having the sheathing flush with the wall as described? It would make continuous foam much easier for me.
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Replies
Drew,
You can do it either way.
One caution though. The chances of your framing being perfectly co-planar with the concrete below is virtually nil. You may be able to make up the difference by shimming whatever furring you are using and end up with a flat wall, but the easiest way to do continuous foam is to include a flashing break at the top of the foundation so that any discrepancies disappear.
I agree with Malcolm. This is one of those situations where builders and designers in different regions or with different backgrounds feel strongly about their system being correct, but either one can work.
I learned to align the outside face of framing with the outside face of concrete, which provides at least 1/2" of wiggle room for adjustments and also makes dimensioning easy and consistent. Now that we have many different wall systems and foundation systems to choose from, it's complicated again, but I still treat the outside face of framing as the most important reference point.
Drew,
We do the sheathing flush with the exterior plane of the stem wall as a matter of course. One thing you very much want to be aware of is to have a capillary break from the foundation to the wood sheathing. We leave a minimum of 3/8" between the sheathing and concrete. We also use a sill seal to break the capillarity at this location.
Joint and seam can work great, but even better and easier is to just use a tape product. We really like the Siga Fentrim product as it sticks tenaciously to the concrete without primers. It also goes on very quickly.
See this article in GBA about a project we did that sounds very similar to what you are proposing. I've also included a pic of our current project where we are using this detail.
https://www.greenbuildingadvisor.com/article/a-budget-minded-passive-house