Air sealing electrical boxes

[matt_i]

I am in the final stages of getting ready to hang drywall.

I spent a lot of time sealing (caulking) the sheathing and various stud cavities in the framing already.

So now I have various penetrations for conduits and NM wires in the top plate, the blue plastic and 4" square metal boxes have their own gaps and holes, I would like to do something to seal them to keep aligned with the strategy.

A couple ideas come to mind...

- spray foam (by the can) have Roxul planned and already bought
- intumescent caulk - probably for the top plate in the stud wall cavities
- foil metal tape normally used for ductwork - thinking it would be used on metal boxes

I do see a lot of shops are spray-foamed entirely which I suspect coats and encapsulates wiring and boxes without a lot of special prep. But, I don't know if there are any rules, guidelines, or cautions that come with trying to do this. Thanks for any thoughts!

 

[alfredeneuman]

.....the blue plastic and 4" square metal boxes have their own gaps and holes, I would like to do something to seal them to keep aligned with the strategy.

Specially made putty pads for boxes are expensive!
This works as well as the putty pads to seal the holes if you just want to block the holes from passing air.
https://www.homedepot.com/p/Protect...indow-and-Door-Sealing-Tape-D897204/100396169

 

[yeldogt]

spray foaming along the upright studs with seams in sheathing -- along top and bottom plate will make a difference. Hit every penetration -- some boxes are a pain .. but I spray

 

[cybrdyke]

Box manufacturers like Raco and Appleton offer vapor barriers for the common sizes of boxes.
No need for intumescent caulk, just use something like 3M FB136.
CD

 

[walta]

I like the looks of this product

https://www.jboxshell.com/

Walta

 

[yeldogt]

I like the looks of this product

https://www.jboxshell.com/

Walta

That looks problematic.

Why I plan on foam from the beginning -- the time, materials and potential mistakes make doing a flash and batt superior for a home. For a garage or shop I think sealing the permitter of the bay gets you close vs trying to get 100 percent at the box.

 

[Angelfire]

Go pick up a pound or two of “Duct Seal”. It’s a putty like material designed not to harden

https://www.homedepot.com/p/Gardner-Bender-1-lb-Plug-Duct-Seal-Compound-DS-110/100212441

 

[alfredeneuman]

No need for intumescent caulk

Intumescent, commonly called fire caulk, may be required where it comes through the top plate, and the blocking below it (fireblocks)

 

[ForceFed70]

Caulking would be my suggestion for top plate, etc.

Sound like you're not running a vapor barrier?

For my shop I used the standard process with a vapor barrier - bought the pre-formed plastic pieces that go around the boxes. Only works with a vapor barrier tho, and needs to be installed at the same time you mount the box (and prior to running any wires).

As mentioned, there are a couple of electrical box manufacturers who offer a built in vapor barrier.

Sealing up the electrical boxes after they've already been purchased and mounted isn't an easy task. I personally can't think of a way that would work well and doesn't require a lot of effort. UNLESS - Have you considered spray foam insulation? Don't need to worry about sealing anything if you use spray foam.

 

[cybrdyke]

Intumescent, commonly called fire caulk, may be required where it comes through the top plate, and the blocking below it (fireblocks)

Fire stop (intumescent) and Fire block (non-intumescent) are two different products. In a stud wall, all you are trying to accomplish is to stop the flow of air thru the holes in the top plate. As long as that's accomplished, fire wont be able to move. Fire block is used for this purpose. As stated previously, 3M #FB136 is the most popular Fire block product. It's considerably cheaper than a Fire stop product.
Fire blocks prevent air movement. Fire blocks prevent fire movement.
Also, local codes vary on this issue.
CD

 

[alfredeneuman]

That prompted me to look up "intumescent", it means swelling when heated.
I made the mistake of equating 'intumescent' with 'fire proof'.