Replies

1. GBA Editor
   Martin Holladay | Nov 03, 2011 05:24am | #1

   Jim,
   Q. "Can I use Demilec AgriBalance open-cell spray foam?"

   A. Yes, as long as you use enough to achieve minimum code requirements. Since that product has an R-value of R-4.5 per inch, so you would need to install at least 8.5 inches of foam to achieve R-38.

   Q. "My main concern is using 3/4" tongue-and-groove pine for the ceiling. Should I use a vapor barrier or not? Thinking of using CertainTeed MemBrain."

   A. You don't need a vapor barrier. However, the building code in cold climates usually requires a vapor retarder. If you install 8.5 inches of spray foam, that qualifies as a vapor retarder and an air barrier. Be careful, though: if you switch to a different type of insulation, especially fiberglass batts, you definitely need an air barrier. Tongue-and-groove boards are not an air barrier.

2. 
   mFK35Pqseu | Nov 03, 2011 03:31pm | #2

   do you have any input on the certainteed membrain. thanks for the info.

3. GBA Editor
   Martin Holladay | Nov 03, 2011 03:36pm | #3

   Jim,
   MemBrain is a vapor retarder; because it has a variable permeance, it is often called a "smart" vapor retarder. It is usually used on the interior side of walls or ceilings that are insulated with fiberglass batts, cellulose, or blown-in fiberglass.

   Since you plan to use spray-polyurethane foam, which is already a vapor retarder, you don't need MemBrain.

4. 
   mFK35Pqseu | Nov 03, 2011 07:59pm | #4

   If the building inspector insists would this be the product of choice

5. 
   wjrobinson | Nov 04, 2011 08:38pm | #5

   Jim, membrain should be fine, the makers of products are the ones to truly ask though. Get your sprayfoam company together with the inspector. Last point, a sprayfoam company worth hiring would have done many installs like yours and know how to handle the barrier/inspector/membrain issue for your particular home and climate. My last sprayfoam project had a vapor barrier paint sprayed on it to comply with inspector.