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Exterior electrical outlets with exterior insulation

I am at a loss how to install and connect the electrical outlets on the exterior of our new build. We are installing 2.5" of mineral wool insulation with 1x4 rainscreen furring and fiber cement siding. None of the electrical boxes (e.g., Arlington) are deep enough to span this much insulation, and I understand that I can not run NM-B through the insulation to a box mounted to the furring. How is everybody else doing this?


Asked by Robert Heinse
Posted Feb 28, 2017 4:23 PM ET



You could install the boxes to the framing and use box extenders, which is what I've done. Or perhaps attaching to the furring would work if you encased the wire in conduit as it penetrates the insulation.

Answered by Nate G
Posted Feb 28, 2017 4:33 PM ET


This may be the same thing Nate is describing.

Scroll down to "goof ring" for covering deeply mounted electrical boxes.

Answered by Steve Knapp CZ 3A Georgia
Posted Feb 28, 2017 10:33 PM ET


You could also run UF-B instead of NM-B. It's approved for wet-location (even direct burial), and costs about 2x NM-B. If you only have a few short runs, it's an easy swap.


Answered by John Ranson
Posted Feb 28, 2017 11:04 PM ET


Perhaps you can simply mount a block of wood, 1~2" thick, on the sheathing, and drill a hole through it for the wire, so the wire is running through solid wood, not insulation.

I'm unsure of whether code requires a weatherproof box in that location, outboard of the WRB, but protected by the siding. It might be prudent, required or not. A plastic box will produce less thermal bridging than metal.

Answered by Charlie Sullivan
Posted Feb 28, 2017 11:05 PM ET


Here is a product similar to one I used on my foam outsulation cladding my home. Go to Amazon and look up "Arlington-DHB1W-1" which happens to be for brick veneer installation. It might be adaptable or you can follow the various leads to other choices.

Your electrician should know what types their supply house has. There are other brands, mine cost about 12 dollars and I set them into the foam and pinned them with some (very) long screws which I removed once the foam sealant I squirted around them set firmly. The wiring is UF as noted by others. There are fittings available that allow you to mate the box to PVC conduit if allowed in your area. I chose to make the effort to provide clean permanent access from interior to the box and protect the wire from critters that might attempt to take up residence in the foam.

My particular box style was made for stucco finishes and the end result is very clean and tidy. I would recommend setting the boxes prior to cladding of whatever type. Be sure to think hard about placement to minimize tricky cuts in beveled siding or brick..

Answered by Roger Berry
Posted Mar 1, 2017 9:50 PM ET



I am in the boat as Robert. Looks like this product will work perfectly. Attached is a link to their catalog which shows the installation in various types of walls. Thanks.

Answered by Jonathan Lawrence CZ 4A New Jersey
Posted Mar 2, 2017 9:53 AM ET
Edited Mar 2, 2017 9:55 AM ET.

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