3/4"

[Don]

I'm insulating my office with R13 batts on the walls and R30 batts on the ceiling. I have 22 electrical boxes on the insulated walls and these boxes will create voids in the wall insulation. There is however about 3/4" of space between the back of the boxes and the exterior sheathing so I am thinking about cutting sheets of styrofoam to the size of the boxes and putting it behind the boxes. Waddaya think?

This will do 2 things. Eliminate that void in the wall (thermal break). And I could get rid of some of this styrofoam packing material that was in our fireplace shipping box.

Is it a good or a bad idea?

(an alternative is to use some of the waste batts (scraps) to *stuff* behind the boxes)

[RicodJour]

Either will work as will a can of expanding foam. Personally, I'm all for the recycling of the scrap styrofoam.

R

[3D Peruna]

Good idea. Up in these parts, we frame w/ 2x6 so we can get enough insulation in. In fact, it's code to use exterior "vapor barrier" type boxes, with gaskets on 'em, then you tape the interior vapor barrier to it. Stupid system, really....

[Don]

Well, I ended up using another technique. I had to cut a piece of the insulation out to make room for the electric box so I stuffed that piece behind the box.