I have a base wall section that has brick, Tyvec, OSB,metal stud with Insulation with a foil backing and gyp board. When I remove the foil backing of the insulation, the water content of the OSB goes down, not up as I expected.
Wouldn't the foil backing trap water in the OSB and removing the foil backing decrease the water content in the OSB?
Water Content of OSB and foil Backing
-
C. Furtaw
- WUFI User
- Posts: 85
- Joined: Tue Jul 19, 2005 2:04 am -1100
- Location: Malvern, Pennsylvania
- Contact:
Water Content of OSB and foil Backing
Charles E. Furtaw, P.E.
Re: Water Content of OSB and foil Backing
Dear Mr. Furtaw,C. Furtaw wrote:I have a base wall section that has brick, Tyvec, OSB,metal stud with Insulation with a foil backing and gyp board. When I remove the foil backing of the insulation, the water content of the OSB goes down, not up as I expected.
Wouldn't the foil backing trap water in the OSB and removing the foil backing decrease the water content in the OSB?
what is to be expected may depend on the specific boundary conditions to which the wall is exposed in your case. If a wall is exposed to a warmer or more humid climate, the moisture may go one way; if the same wall is exposed to a cooler or less humid climate, the moisture may go the other way.
If the calculation result is not what you expected you should first check for possible calculational problems by making sure that the moisture balances in the info window displayed at the end of the calculation are okay, and that you do not have an excessive number of convergence failures.
If the calculation appears okay, maybe your expectation was mistaken. Look at the film to see when the moisture goes where. Maybe what's going on is plausible after all, and the moisture is trying to go a different way than you expected. Maybe the wall is exposed to such warm weather (or high solar radiation) that it's trying to dry out but was previously trapped by the foil.
Another possibility may be that you unintentionally entered a wrong number somewhere, leading to results that are computationally correct but based on erroneous input. Again, watching the film may reveal implausible temperatures at some point, or a conspicuous lack of moisture flow where moisture is expected to abound etc.
Regards,
Thomas