For recently projects in Houston, Texas, I have specified an air and vapor barrier (WR Grace Perm-A-Barrier Wall Membrane) directly over the exterior wall sheathing on metal stud framing. So far, this appears to be a successful installation.
Could this type of membrane, being self-healing, be installed over concrete block with metal lath secured to the concrete block with screws?
What happens when interior desecrate..I mean designers decides to have vinyl wallcovering (or some other relatively vapor-impermeable “finish”) on the interior face of an exterior wall in S. Florida…in addition to whatever vapor barrier/retarder the architect may have designed into the wall assembly? Hmmm..interesting to see what would happen?
I am surprised that there is still this much questioning of vapor barriers. For specifiers and architects requiring data on vapor barriers, air barriers, and mold development in exterior wall systems, I would suggest going into the CSI website. Click on “Construction Specifier”. In the “Keyword Search”, type in “Vapor Barriers”.
The Construction Specifier has several very good articles which cover the topics indicated. They detail the problems, failures and solutions.
A final note for specifiers and architects working on Florida projects: Never place vinyl wallcoverings on the interior of exterior wall systems. You may be creating vapor barriers on the interior and exterior of the wall, which would entrap moisture within the wall system, resulting in mold growth!
To All concerned with this issue. I refer you to the AirBarrier Association of America
1600 Boston-Providence
Walpole, MA 02081
1.866.956.5888
1.866.956.5819Fax
Everything you want to know about who, WHAT, WHEN,WHERE, and WHY may be found here.
We are members of this organization (as a manufacturer). I have attended a seminar conducted by the group in Seattle, Wash. and I can assure you that the information is out there and they can be of great service.
Florida exterior walls do not have air barriers, sheathing, studs, brick, none of it!!! The exterior walls are painted stucco on concrete block (exterior side) painted gypsum board on furring on rigid insulation on concrete block (interior side). Should the rigid insulation have foil backing (a vapor barrier)?
Here in Massachusetts the industry is moving towards new designs for wall systems. We needed to take into account the code-required air barrier. The most effective solution has been to combine the air barrier and vapor retarder, and move the insulation outside of the ab/vr (using ridid foam) into the wall cavity. This is a big change from batt-stuffed walls with interior poly.
It still makes no sense to me that anyone in Florida would put a vapor retarder near the interior of a wall assembly. Maybe Florida needs to find new types of wall assemblies, too. Has anyone run a WUFI-simulation on this? Or requested assistance from Grace Construction Products, who can run moisture simulations? I’d start there.
I am beginning specification work on a project in Eugene Oregon where the designer is proposing the following exterior wall system. Any thoughts related to placement of the vapor barrier or any other aspects of this assembly?
Interior gypsum board over 6 mill polyethylene vapor barrier over furring channels, over CMU with unfilled cores.
Exterior EIFS system with waterproof adhesive with 3 inches of EPS insulation.
Other than the fact that the vapor barrier will be penetrated with every drywall screw, electrical and communication box and picture hanger? What could possibly be wrong with that?
My point exactly! Many architects/engineers where I practice (south Florida), feel the rigid insulation must have foil backing (aka vapor barrier)a northern climate practice. However, by the very nature of construction, the foil backing is not a completely sealed barrier. Therefore, the wall is still able to breath and in reality the the foil backing is useless and a waste of money.
There are two ways that moisture travels across envelope assemblies - air transport and diffusion. Both need to be addressed. Foil is a vapor diffusion retarder (as are polyethylene and kraft paper). If the vapor duffusion retarder has holes in 10% of its surface area, it is 90% effective. If, however, you have holes in 10% of the air barrier (what you need to control air transport of moisture laden air), serious problems could ensue. Read Lstibureks books for a full explanation.
Joe Lstiburek PhD advises not to use vapor barriers in exterior walls in Flordia. That I know. However, some of my south Florida colleagues disagree with Joe. I believe they disagree because they’re transplanted northerners applying northern logic. Hence, I seek a third (or forth) opinion.
Not that I have any association with this, but Mr. Lstiburek is doing a seminar in the Twin Cities that will touch on this subject:
http://www.cala.umn.edu/cps/spring2004/6570.html
And, good information to know at the Building Science post.
He will also be speaking at the CSI Puget Sound Chapter in Seattle, WA on May 13.
… regarding the wall assembly in Eugene – and the fact that most insurance companies are not covering EIFS assemblies, there are municipalities that won’t allow it in their jurisdiction, and it fails more often than nearly any other exterior wall system, its clearly the recommended system for the Eugene Oregon climate where even GOOD exterior wall systems often leak. Are you sure this guy is a “consultant”?