Airtight Device Box and 5/8 Drywall or Double Drywall Installation
Wondering how installers who use the plastic airtight electrical boxes with the foam gasket (e.g. Nutek brand), deal with either 5/8″ drywall or even double 5/8 drywall which is common in sound dampening installations. There are 5/8″ and 1-1/8″markings on these Nutek boxes, suggesting that the installer position the box slightly further out on the stud to accommodate the thicker drywall. But in practice, wouldn’t this just set the foam gasket further off the studs causing the drywall to jut out where the foam gasket is? So to get the drywall tight against the stud, you would then have to cut the drywall out around the foam gasket, defeating the whole purpose of having the gasket. Hope this question makes sense. Just looking for best practices using these types of boxes to ensure a good air seal. Is the only solution to install the box tight to the studs, and use box extenders?
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Replies
ZiggyC,
Yes you are right. You have to mount the box so the gasketted flange is tight to the stud. I have no idea why they would show other depth markings.
If you are using 5/8" drywall most codes allow some wiggle room as long as the finished surface is noncombustible. For two layers you are into box extenders - but I can't think of a situation where you would have two layers on an exterior wall.
"314.20 In Wall or Ceiling.
In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (1⁄4 in.). In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall be flush with the finished surface or project therefrom."
Thank you for the reply.
I believe two layers of drywall is pretty common for basement home theaters where you are trying to avoid excessive sound leakage through the rest of the house and outside to the neighbours. My situation is an entertainment room that will also be used as a DIY music studio in a below grade basement. Hoping to have thick enough walls to absorb at least some of the racket of a drum kit/guitar amplifiers. I'll be using 3/4" Sonopan sheets (a Canadian thing) and then 5/8" drywall, and maintaining air tightness is crucial for stopping soundwaves. Looks like I will definitely be into box extenders to make up the 1-3/8" distance to those airtight electrical boxes.
ZiggyC,
Do any of those below grade walls need gasketted boxes? For sound attenuation they are better off with putty covers or foamed from the back, and regular boxes can be mounted flush with the two layer of drywall.
The wall is half below grade, half above in Zone 5. The boxes would need to be tied into the vapor barrier. In retrospect, I wish I'd gone with metal boxes and putty, but I went with the Nutek boxes and the electrical work is all completed.
I've always mounted those flush with the stud. The lip is set for 1/2" drywall but works just as well for a single layer of 5/8". For double layer, you will need extensions.
I think the markings on the box are for the non-flanged version, they must use the same injection molding die for both parts.
If you have the option of installing the box as you are installing the drywall, my favorite option is the airtight old work box "Carlon 1-Gang 18 cu. in. Old Work Draft-Tight Electrical Box". You may just google it. Home Depot near me carry it.
If you make the cut tight and sit the box right (better to practice on a scrap piece of drywall ahead of time) they hold up firmly and the outlet ends up at the perfect depth every time. On this particular model, the screws are long enough to accommodate two layers of 5/8 drywall.