ECN Forum Forums General Topics of the Trade General Discussion Area Fiberglass insulation

I want to know what the proper way is to install fiberglass insulation around 1) Wires running along/thru studs, 2) Around Outlet Boxes, and 3) Around Light fixtures, where it will be hot. (All NM-B, no conduits or ac). (I know that nobody is liable for any advice blah blah blah legal stuff here blah blah blah)

You might want to ask that in the insulation forum.

In VA. our inspectors require us to remove the paper backing within 6" of a recessed type IC fixture. The fiberglass batt can be snug to the fixture. There doesn't seem to be any other problems around boxes or NM-B. We do tuck it behind the box to satisfy the energy code and help prevent drafts thru the outlets.

The important thing with fiberglass insulation is that you don't want to compress it. If you do the R value will be less where it is compressed.

With that in mind a good insulation installer will do a knife cut partially through the batt from the backside to put a horizontal cable in the center of the insulation without compressing it. The same can be done for vertical runs only the insulation can be split with your fingers to accommodate the cable.

I like to see the space behind a box (between the back of the box and the sheathing) filled with uncompressed insulation. You again would split the insulation with your fingers, slide a layer behind the box then cut the front layer away around the box. I think that the thin uncompressed layer behind the box has a higher R value than the whole thickness shoved in there.

Light fixtures in insulation should be type IC so they can (and should) be completely covered following the same rules I gave above if applicable.

-Hal