Almost ready to start the rewiring of my house, just need to finish up
my plans. I am probably going to go with plastic old work boxes that
are 3.5" inches deep in most situations.
This is going to leave me with 3/8" at most between the back of the
box and the sheathing on my outside walls(3/8 drywall).
Any reccomendations on how to insulate behind the boxes and around the
sides of them?
Use a latex spray foam like that recommended for window installation
at the back of the box. Expansion won't bother the box installation.
Then cover the remainder with fiberglass bats, whatever.
Do you really have 3/8" drywall exterior sheathing?
No. I have 3/8" drywall on the interior, guess I should have been a
Although these houses were built so cheaply I wouldn't doubt they used
3/8" plywood for sheathing.
I did some work on a Levittown house years ago and the sheathing was
some type of fiberboard that disentegrated after getting wet. Not
sure what it was but seemed like it was the same stuff that gets layed
under a rubber roof.
On Mon, 15 Mar 2010 11:00:33 -0700, Limp Arbor wrote:
We have something very like that in our garage (which, going by the
bakelite electrical fittings I pulled out of it, must have a few years on
the clock). It does actually say 'sheathing' on it in big letters, but
the smaller text beneath is all but unreadable after so many years. I
know exactly what you mean about damp - it's rather horrible stuff if it
ever absorbs moisture.
(I'm aiming to get another 4 or 5 years out of that garage, then I'll
pull it down and build something less crappy :-)
*One way is to use a vapor box around the electrical box:
Another method that I have used with outdoor receptacles that have recessed
boxes is to wrap the electrical box with a putty pad. They can be a little
Others may suggest spray foam. I have never tried that.
You could also use 4"x4"x1.5" square electrical boxes. That will give you
room to put insulation behind.
I would pack the space with the highest R-rated foam sheet or spray or any
other insulation that will give you the most insulating and vapor barrier,
that you can obtain. If you have to buy a sheet, cut it into squares about 8
to 12 inches and fit behind each box even if the ground and clamp screws
penetrate into the insulation. While 3 1/2 inch deep boxes are great for
wiring, you may be better in locating some 2 1/2" deep boxes for the outside
walls, this will give you much better insulation and prevent condensation
from forming inside the backs of the boxes, which is never good.
Using the latex spray foam works pretty good, but turn the power off
first. Latex foam is water based - and if it expands and hits the
terminals on the outlet it can (and usually will) sizzle and heat. The
propellant in that stuff is basically propanol, so you need to take
After it has set, shave the excess out of the box and turn the power
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