Replies

1. 
   wjrobinson | Jan 10, 2014 02:36pm | #1

   Drywall installed leave a row of subfloor unfastened.
   Fill from top with cellulose.
   Done.

2. GBA Editor
   Martin Holladay | Jan 10, 2014 02:45pm | #2

   David,
   A.J. is certainly correct that cellulose is a much better solution than fiberglass batts, especially for this kind of floor assembly.

   Most experts suggest that the insulation should be in continuous contact with the subfloor. Joe Lstiburek is an outlier -- he says that it's OK to let the insulation sit on the drywall, with an air space between the top of the insulation and the subfloor. But the Lstiburek approach only works if you install spray foam at the rim joist, and if you are meticulous about sealing penetrations at the drywall ceiling and subfloor. Even then, the approach won't work as well with batts as with cellulose.

   Don't worry about the kraft facing. It isn't important. Your subfloor is already a vapor retarder.

   For more information on a variety of solutions to this problem, see How to Insulate a Cold Floor.

3. 
   talldave | Jan 10, 2014 04:32pm | #3

   AJ, Martin, thanks for the feedback. I recognize the article now and it didn't come up when I searched for it.

   Part of the problem is that if I spec cellose, it won't get installed, because it means a different trade has to come in. Batts and caulk and rigid board can be installed by guys who are already on site. The 1-1/2" of rigid on the underside helps too.

4. 
   wjrobinson | Jan 11, 2014 12:55pm | #4

   Dense packing cellulose around the perimeter at the beginning of the install solves the air leaks. Cellulose also will fill in truss webs. You can buy it material and labor included for a set fee.

   Fiberglass is going to let air move and make it less effective. One air leak in rigid foam and rigid foam's R value is 0.

   Good luck.
   Aj

5. 
   Mike BIB | Jan 12, 2014 11:26am | #5

   I would spray open cell to the underside of plywood. Foam is an air barrier, foam will fill in around web trussing.
   Insulation will be in contact with underside of floor.
   We do spray foam if you need a contractor in Chicago area.

6. 
   wjrobinson | Jan 12, 2014 04:49pm | #6

   Mike, what would R-30 cost for a 24'x24' area?

   For;

   1-open cell
   2-closed cell
   3-cellulose (seems you would know the other trades prices)
   4-fiberglass with the rigid foam layer

   Bang for the buck to me is cellulose. I could even set up a laborer to do the install. Not against open cell at all, but am trying use much less of it in the future.
   aj

7. 
   SprayfoamAshley | Jan 14, 2014 11:44am | #7

   Hey David,
   Closed Cell Foam will work really well for your project. You can get the insulation closest to the conditioned area, it adheres easily to the surface and it will give you an air-tight seal so that the cold Chicago air can’t travel up into the room above.

   I would say about half of our customers insulate with Foam It Green only and the other half does a combination method. You will get great results with either approach.

   Foam It Green’s closed cell foam has an R-Value of 7 per inch so if you local inspector is strict you would need 5 inches to get an R-30.

   If you choose the combination method I recommend first adhering R20 rigid foam board to the underside of the subfloor. Once the foam board is fully adhered you can spray 1 ½” to 2” of closed cell Foam It Green over the board to get the extra R-Value and air-tight seal.

   And a few extra bonuses with going the Foam It Green route- you can quickly and easily do the job yourself, our formula resists mold growth on the face of the foam and we’re right in your neighborhood. We have a pickup location just outside of Chicago.

   Our website is Sprayfoamkit.com if you would like to take a look at our kits.

   When are you planning on doing the project?