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SIPs over 2X roof deck
Last Post 31 May 2008 01:58 AM by The Panel Guy. 1 Replies.
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Mr. NUser is Offline
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29 May 2008 05:18 PM

House in Big Bear Lake, CA with 100 psf snow load.
Using 8" SIPs over 2X roof deck for insulation.
Will a vapor barrier between 2X deck and SIPs cause any problem with moisture getting into the decking or should I omit the vapor barrier and put a shallow ventilated space over the sips to allow all moisture to escape?
Thanks.
The Panel GuyUser is Offline
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31 May 2008 01:58 AM
Mr. N,

It is not typically to install a full two sided SIP over 2 x decking. There is a product call Insul-Lam that is a one sided SIP that is typically used for your application.

You do not want to use a plastic membrane over the top of your decking and under your SIP panel. The plastic membrane will pick up moisture from the living space below and
sweat. You will actually end up trapping moisture between the plastic and the top of the 2 x decking that will eventually bleed through. It wold be okay to install 15 or 30 lb felt. It won't react
to the heat rising from below like a platci membrane will.

You can also purchase "vented" Insul-Lam.

The Panel Guy
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