Replies

1. GBA Editor
   Martin Holladay | Oct 29, 2018 05:32am | #1

   H.N.V.,
   Q. "I want to insulate wooden pre-built shed with rigid foam. I’m confused about which side goes toward the wood wall."

   A. You haven't described the construction details of this shed, but I'm going to assume that you are describing a shed with studs and exterior wood sheathing or sheathing/siding. You have two choices: (1) The "cut-and-cobble" approach (requiring you to cut narrow rectangles of rigid foam and insert the rectangles between the studs), or (2) The "continuous insulation" approach (in which your install rigid foam on the interior side of the studs in a continuous manner).

   For more on cut-and-cobble, see "Cut-and-Cobble Insulation."

   Q. "I’m confused about which side goes toward the wood wall. I think the tin foil side but not sure."

   A. There are lots of types of rigid foam on the market. You can purchase rigid foam with aluminum foil facing -- either on one side of the rigid foam or both -- if you want. You can also purchase rigid foam without a foil facing.

   If you choose to buy rigid foam with a foil facing, you will get no R-value benefit from the aluminum foil layer unless it faces an air space. Except for that fact, it makes no difference which directly the foil faces.

   Note that exposed rigid foam, with or without foil facing, is a fire hazard. If anyone intends to live in this shed, the rigid foam needs to be covered with a layer of drywall for fire safety.

   Q. "Insulating the floor on the outside is nearly impossible to crawl under, so can I use the rigid foam on floor inside and put plywood or something on top?"

   A. Yes, you can do that. A continuous layer of rigid foam on top of the existing subfloor, plus another layer of plywood on top of the foam, will work fine.