Haven’t seen these used yet, but MSHA is now mandated the use of air tight electrical boxes in outside walls.
First is a large plastic box (Photo 1>) that you nail to the face of a stud, then install a standard electrical box inside it. It’s large enough to handle multi-gang electrical boxes. Cut a slit in the side of the box and push the cable through it and wire the box as you normally would. Caulk around the cable where it penetrates the box to seal it. If you’re using a plastic vapor barrier, seal it to the box apron with an acoustic (non-hardening) caulk. If you’re applying drywall without the vapor barrier behind it, caulk the drywall directly to the box.
Another option is an air-tight electrical box (Photo 2) that uses a soft rubber gasket that seals to the drywall. The box also is wrapped in a rubber skin that seals the cables. Make a small slit in the rubber and push the cable through. Install and wire it as you would a standard box.
You can also order these boxes at electrical supply stores.
1. The Lessco Air-Vapor Barrier Box is nailed to the stud and allows use of standard electrical boxes. Slit the top to insert wire, then use caulk to seal as shown. These boxes cost $2.25 to $2.50 each. (Visit www.lessco-airtight.com or call 920-533-8690 to find a local dealer.)
2. NuTek’s airtight electrical boxes use a foam gasket around the drywall flange and where the cable enters to seal out air and are available at most home centers and hardware stores. They cost $2.50 to $5.50 each.