Cutting Insulation around Outlets, etc.


Old 02-14-03, 05:18 PM
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Join Date: Jan 2003
Location: USA
Posts: 169
Cutting Insulation around Outlets, etc.

Hi, All -

What is the best way to cut insulation around outlet boxes and recessed-light cans? Should I measure it out and cut before I hang it, or hang it first and try my best with a knife/scissors while it is in between the studs/joists? I am currently installing R13 with kraft-paper backing on the walls, and thicker stuff (yet to be bought, but it will have a kraft-paper backing) for the ceiling.


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Old 02-14-03, 08:51 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873
Measure twice, cut once

A scissor is best to cut out for the outlet/switch boxes. You can do it either way. The way I like doing it is separating the back part of the insulation that fits behind the box and installing it. Then install the layer with the vapor barrier over that and the box. Using the box as a reference, I cut the box out of the insulation.
Old 02-18-03, 01:56 PM
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Why do you want to use kraft faced? It is not a vapor barrier, it dosen't even have a rating. The paper deteriorates, attacts silver fish and the pitch used to glue the paper is extremely flammable. To top it off the FG is less than 10% eff., condensates moisture, allows mold to grow, carcenogenic, stinks, and loses up to 50% of its "R" value.

Check out 97% radiant barrier insulation. It has none of the problems listed.

Thank you for considering my opinion.
Old 03-26-04, 08:37 AM
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Join Date: Mar 2004
Location: Vancouver, BC
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Question - or two..
1.- Are those pre-formed poly vapor barrier 'boxes' worth it.. or is 'resercon's method, by tucking the insulation behind the box the preferred method. That VB box seems like more work..and big for a 2x4 wall.
2.- Which is the preferred type of box for the inside of exterior walls? Plastic or metal?
Old 03-26-04, 11:37 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
rbisys dont try and sell that R/B to people

'resercon's method, by tucking the insulation behind the box the preferred method.
Go for it and just use the plastic boxes. We still put a poly over it all before we dry wall. Windows and all the outlets in one piece. Then after the drywall and paint or what ever is done Then cut out the poly at the windows and boxes. Sure help keep things clean. ED
Old 03-26-04, 06:50 PM
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Join Date: Mar 2004
Location: Vancouver, BC
Posts: 1,045
So, Plastic boxes on exterior walls are preferred. Then insulate in behind and around that plastic box, VB..and tape the VB around the box for a tight fit. Thats what you mean? And grounding the plastic box? With its clip? - process.
Thanks a mil.

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