Do any of the double-stud wall details enclose air conditioned spaces?

I see that you now have double stud wall details in your detail library. These details are probably from projects in zone 7A, so a poly vapor barrier may be used, but are any of these buildings air conditioned? If so, how does that affect the use of the vapor barrier in this zone?

Asked by Stephen Martinson
Posted Wed, 03/13/2013 - 14:09
Edited Thu, 03/14/2013 - 06:20

Tags: Energy efficiency and durability

1.

Stephen,
Good question. You'll notice that the notes that accompany GBA detailing interior poly include this warning (found at the "Key Materials" tab):

"Although 6-mil interior polyethylene (installed as a combination air barrier and vapor retarder) is shown in some GBA details, it should only be included in buildings located in very cold climates (for example, Climate Zones 7, 8, or the colder sections of Climate Zone 6). In most areas of the U.S., interior polyethylene can cause problems, especially if the building is air conditioned. For more information, see Vapor Retarders and Vapor Barriers."

(The details came from Rachel Wagner, a Minnesota designer.)

Answered by Martin Holladay, GBA Advisor
Posted Thu, 03/14/2013 - 06:05

Edited Thu, 03/14/2013 - 06:14.

2.

Martin,
I contacted Rachel Wagner and here is what she had to say about air conditioning in this zone with double stud walls:
"None of the houses I've done have air conditioning. If you have air conditioning, I would not recommend using poly as the interior air barrier/vapor retarder. I would go for a polyamide film product like CertainTeed MemBrain.

and be sure to use plywood and/or fiberboard as the exterior sheathing, not osb, and a rainscreen, to really allow the wall to dry to the outside."

Answered by Stephen Martinson
Posted Thu, 04/11/2013 - 11:38