Replies

1. GBA Editor
   Martin Holladay | Sep 26, 2013 01:20pm | #1

   Geoffrey,
   You forgot to tell us your location or climate zone.

   Q. "Do I need any type of additional barrier between the webbing and the drywall?"

   A. No. But you need to pay attention to airtightness when you install the drywall.

   Q. "Is it a problem to add a layer of foam to the outside of the wall before I put on a housewrap?"

   A. I usually advise people to choose just one place to put their foam insulation, and to avoid sandwiching wooden components between foam layers. If you were planning to install rigid foam on the exterior side of your wall sheathing, it would have been better not to insulate with rigid foam between your studs. Cellulose would have been fine there.

   In general, taking perfectly good rigid foam and cutting it into narrow strips to insert between framing members is usually a bad idea. It's always better to install foam as a continuous, uninterrupted layer.

   In your case, it sounds like it's too late. You can probably install more rigid foam on the exterior of your house, as long as you do the work in very dry, sunny weather -- you don't want to trap any moisture in your wall -- and as long as you do an impeccable job with your wall flashing. But don't make the same mistake again, OK?

   Q. "Can I add 1 inch foam to the underside of the [ceiling] joists and attach drywall directly through the foam or would I need furring strips (If so I will skip this)?"

   A. It's best if you can install furring strips. But if your ceiling height can't easily accommodate the extra 3/4 inch, you can skip the furring strips. You'll find it challenging to screw the drywall through the foam, but the work is possible.

   Q. "Do I need some sort of vapor barrier with either option: foam or just drywall and insulation?"

   A. No, you don't need an additional vapor barrier (although some types of rigid foam amount to a vapor barrier). As with your walls, the important step is to pay attention to air sealing.

2. 
   user-2423385 | Sep 26, 2013 10:11pm | #2

   The XPS insulation I got for less than R-13 fiberglass and was already in 16" pieces right from the factory so I didn't cut it. I wanted to put R-1 pink foam on the outside to make a smoother surface as I will be putting the house wrap over ancient siding (actually a neighbor just asked to buy some for his restoration...so there will be a very little less :) but no big deal to leave it out.

   Another question...I am installing a small amount of recessed lights (IC type) in the ceiling. I noticed there are a few small gaps where the wires enter the can even though it is rated as airtight. Can I put some caulk in those gaps or would it be wiser to simply build small enclosures around them. Thanks

   BTW..I'm in Wisconsin..north eastern. Are there any good links to Air sealing techniques?

   thanks

3. GBA Editor
   Martin Holladay | Sep 27, 2013 08:13am | #3

   Geoffrey,
   Yes, you can seal the holes where the wires penetrate the recessed can housing. But it would be even better if you didn't install any recessed cans at all in your insulated ceiling. For more information on recessed can lights, see Recessed Can Lights.

   Here are some links to articles about air sealing:

   Air Sealing an Attic

   Airtight Wall and Roof Sheathing

   Air Sealing With Sprayable Caulk

   Questions and Answers About Air Barriers

   Getting the Biggest Bang for Your Air-Sealing Buck

   New Air Sealing Requirements in the 2009 International Residential Code

   Energy Upgrades for Beginners

   Air-Sealing a Basement