Sight-built SIPs detail — leave the middle foil face?
brian_mcdonald
| Posted in GBA Pro Help on
Martin:
As a follow up question to a previous one:
I am going with the “sight-built sip” approach.
Zip sheathing taped then a double layer of 1″ eps foam and 1/2″ osb on the outside with an additional layer of building wrap.
The sheets came foil faced.
Q:Does it matter if I leave the foil on the 1″ layer attached to the sheathing? (sandwiched between the 2 layers of foam) Will it interfere with moisture flow away from the house?
It peals off fairly easily so that is an option.
Brian
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Please provide details like climate and whether you have any insulation between studs, or a link to the previous thread if we are supposed to get those from there. Thanks.
Climate zone 5a
24" oc 2x6 framing
Dense pack cellulose insulation
Brian,
Like Charlie, I don't know which previous question you're talking about. If you know where you posted your original question, it's always a good idea to include a link.
In any case, the answer to your question is simple: the foil facing can be left intact. One or more layers of foil won't make any difference here, because you can't expect this type of roof assembly to dry to the exterior in any case.
Your question was addressed in this article: How to Install Rigid Foam On Top of Roof Sheathing. In that article, I wrote, "Some builders wonder whether there will be any problems if two or more layers of rigid foam have multiple vapor barriers (as happens when several layers of foil-faced polyiso are stacked on top of each other). The answer is no — this won’t cause any problems."
If you haven't read the article yet, I urge you to check it out.