SIPs - Seam Taping
Last Post 29 May 2015 03:43 PM by Lbear. 23 Replies.
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27 May 2015 05:25 PM


I believe GoSolar is confusing vapor permeable with vapor impermeable membranes and is viewing them as the same, vapor barrier.

Posted By acobb on 27 May 2015 10:36 AM
Speaking of garbage in-garbage out: The recommendation to put a vapor barrier on the outside (cold side) of a SIP structure in climate zone 6 is ludicrous. Don't do it!
As a SIP professional with 25+ years of experience I can assure you that is bad advice. The consulting work I do nationwide often involves forensic investigation of SIP projects gone bad. It is not uncommon to find an exterior VB installed in cold climates which leads to trapped moisture.

good luck
Al Cobb

I agree that vapor impermeable membranes should not be used on top of OSB roof SIPs. That is a recipe for eventual disaster. Lot of confusing info out there but I have concluded that it is not the best practice.

A vapor permeable membrane should be used and a venting channel above the SIP should be utilized. Any trapped moisture can pass through the vapor permeable membrane and the drying channel will allow for proper airflow to dry it out.




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27 May 2015 06:00 PM
not confused at all, I agree on this rare occasion with you about the membrane just n ot the air space with old fashioned belt & suspenders approuh on batten systems
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29 May 2015 10:54 AM
Read Structural Insulated Panels (SIPs) by Joe Lstiburek. It is highly informative and is a must read for anyone building with OSB SIPS. Having said that, I used 2x4's for spacing on my own cold roof after much deliberation. It only took a couple extra days the cost was minimal and I sleep much better with the added protection and "sacrificial layer". I furred out my Hardie siding with 1/4" strips and feel better about that as well. My house is only 5 years old now but so far no issues. By the way, I only taped the inside seams not the outside and I taped them all, even though my detail only required taping the roof seams.
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29 May 2015 03:43 PM
Posted By vb on 29 May 2015 10:54 AM
Read Structural Insulated Panels (SIPs) by Joe Lstiburek. It is highly informative and is a must read for anyone building with OSB SIPS. Having said that, I used 2x4's for spacing on my own cold roof after much deliberation. It only took a couple extra days the cost was minimal and I sleep much better with the added protection and "sacrificial layer". I furred out my Hardie siding with 1/4" strips and feel better about that as well.

Joe Lsitburek also wrote the Building Science Corporation study and article on SIPs. Physics are a law of nature and they cannot be changed. Moisture will eventually get its way into wood substrates like SIPs and one cannot prevent that from happening. All one can do is allow a proper and expedient drying path and capability for that moisture and let the SIP OSB skin dry to prevent damage, rot and eventually failure.

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