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.