Replies

1. 
   jklingel | Dec 21, 2011 05:58pm | #1

   I'm just a diy guy, so fwiw.... Use the best R you can, that is designed for your space. There are better insulations than FG, though. Make certain you air seal impeccably. Why are you leaving the asbestos siding on? Won't that be a real PITA to work over? The system as described is probably permeable enough, but I would not want to work over that siding. I'd strip it all, install the foam, house wrap, a rain screen, and new siding. Yes, caulk all penetrations that aren't taken care of otherwise.

2. 
   fgmei35nCV | Dec 21, 2011 09:19pm | #2

   Thanks John. To answer your question, it's typical to go over this type of siding because the alternate of removing it needs to be done according to EPA rules, thus costing to much, taking longer, neighbor issues, etc. I'm now thinking of adding foam/rigid board on the interior studs (still filling bays w/FG) and over the ceiling sheetrock under the ceiling beams. Any thoughts? Are there any condensation issues?

3. 
   jklingel | Dec 21, 2011 11:24pm | #3

   I was wondering about the EPA deal and that asbestos siding. Bummer. I am not the expert on foam inside, but the more insulation there is inside the more likely the outside is going to be cold and condense. It is usually recommended to put the foam on the outside, like a REMOTE-type wall. Martin has a blog here to do w/ How Much Exterior Foam, or something; a search should find it. That should help you determine how much to use. I would never put foam on the inside over sheet rock. The sheet rock is likely painted w/ several coats, making it rather impermeable; I would expect condensation issues there.

4. GBA Editor
   Martin Holladay | Dec 22, 2011 04:46am | #4

   Jeffrey,
   Q. "Is it better efficiency to use R-15 than R-13?"

   A. Yes. The higher the R-value, the better the insulation. If you want the maximum R-value per inch, you could install closed-cell spray-foam insulation. Three inches of closed-cell spray foam is rated at about R-20.

   Q. "Will the housewrap be detrimental over the existing asbestos siding in any way?"

   A. No.

   Q. "I'm now thinking of adding foam/rigid board on the interior studs (still filling bays with fiberglass) and over the ceiling sheetrock under the ceiling beams. Any thoughts?"

   A. It's possible to install rigid foam on either the exterior of your walls or the interior. In most cases, it makes more sense to put the rigid foam on the exterior; you probably don't want to put foam on both the interior and the exterior, however, because it's best if the wall assembly can dry out in at least one direction.

   You have said that you want to install XPS on the exterior of your walls. That makes sense -- so you don't need more rigid foam on the interior. However, if you want to install rigid foam on your ceiling, followed by another layer of gypsum drywall, there's no reason you can't.