Leakage around electrical boxes may not seem significant, but because there are so many of them they add up quickly. Most electrical boxes on exterior walls and ceilings in new construction will already have some form of box or gasket system installed by the electricians. It is important to seal any holes where the wires enter the electrical box to reduce leakage. In renovation jobs it is likely that no system will be in place. In this case the client will need to contact an electrician to have a system installed.

Incorrect Method

After installation of the polyethylene the boxes must be sealed to it to maintain a continuous barrier to air infiltration. This is most commonly done using acoustical sealant between the layers. It is important to note that these layers must be fastened to one another. The above method has no way to fasten the poly box to the polyethylene sheet. While this may be sealed initially, it will likely not stay that way. Remember that air barriers must be constructed rigid and strong enough to withstand air pressure differences.

Correct Method

If gasket boxes are used, then the drywall will compress the polyethylene onto the gasket providing a seal. If an extremely air tight envelope is desired, then this gasket should be further enhanced by using acoustical sealant.

If a poly pan box or piece of polyethylene sheet is used, they must be pulled to the inside of the polyethylene. Acoustical sealant is then used to seal between the layers and an approved tape is used to fasten the poly pan box to the polyethylene sheet. This will keep the seal in place long term.

The photo above shows a typical polypan box before any sealing works has been done. Note that the insulation in this photo is very poorly installed.