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Community and Q&A

Vapor barior on SIPs in a hot humid climate

hughsdb | Posted in Green Building Techniques on

We have been asked to repair siding on a sips panel house in a hot humid climate. Our client has been advised to have us put a vapor barrier over the panels before installing the siding. This will essentially put the OSB between two vapor barriers… in a hot humid climate. This does not seem like a good idea. What do you think?

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  1. Expert Member
    Dana Dorsett | | #1

    A vapor barrier on a SIP is a lousy idea in any climate.

    A weather resistant barrier (such as housewrap or #15 felt) is an absolute must.

    Is the client perhaps conflating the two?

  2. GBA Editor
    Martin Holladay | | #2

    Dana is right. For more information, see All About Water-Resistive Barriers.

  3. hughsdb | | #3

    Thanks. That is what I would have figured. I'm even a little reluctant to use felt. Maybe I will pre-crinkle it to give it more of a drain pan and/or set up an upper vent to drive more air through it.

  4. Expert Member
    Dana Dorsett | | #4

    Good old #15 felt is more vapor-open than OSB, and completely not a problem. Houswraps are more vapor open than felt. Both are greatly enhanced if you can establish even 1/8" of ventilated air space between the s siding and the felt or housewrap, which provides both a capillary break against wicking rain/dew moisture, and a drying path for both the siding and the OSB.

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