Updated: Nov 16
I have seen it time and time again, improperly installed plastic vapor barriers around electrical boxes. Some people might not think that it is not a big deal, but I will ensure you that this is something you should avoid doing.
The installation of vapour barrier around electrical outlet boxes is actually not an electrical code requirement; it is a requirement of the Alberta Building Code that is enforced by your municipal building inspection department. I thought that I would write an short article as to why we install them and what happens if you don't.
In the above photo, there is a picture of what happens in the winter when it gets really cold and there is no vapor barrier on the electrical box in the wall. Frosty!
Why are Vapor Barriers Needed?
Well, here in Canada we have all 4 seasons of weather. spring, summer, fall, and the dreaded winter. As the seasons change, there is temperature differences in between outside and inside temperatures. If there is no vapor barrier, the difference between the two will cause diffusion to happen and moisture/dampness to build up inside the walls. With the excess moisture, this has the potential to cause mold and rot.
Installing a vapour barrier will make sure that as the name suggests, a barrier between warm and cold. It will also help to eliminate drafts in the building and overall energy efficiency.
What Types of Vapor Barriers are
Available for Electrical Boxes?
Plastic vapor barriers come in many shapes and sizes depending upon what size the electrical penetration is. You can buy precast sizes that will fit most common box sizes. Some common examples would be for an electrical octagon box, a plug or switch box or for square electrical boxes.
Some people might ask the question, what if the electrical box is an odd size or they do not make a precast one for my device? The answer is simple. As long as the vapor barrier is maintained and taped or sealed with an approved sealant, you should have no issue. All you need is a piece of poly that seals the penetration up and does not allow air to leak through.
Ideally though, If they make a precast barrier, try to use these as it will allow for a tighter seal and allow more insulation to be installed closer to the wall. The current standard for thickness on the plastic is 6 mil poly.
Alternatives to Using Plastic as a Barrier
If you are looking for a different way to seal a wall or a ceiling and create a comfortable space, you might consider use of spray foam or ICF walls. These types of insulation will not mold or hold moisture which is huge plus.
Another type of a CSA approved plastic electrical box on the market has foam gaskets built right in and seals once the drywall is installed overtop. These are great and saves having to marry the plastic boot and the plastic on the wall or ceiling before dry walling.
Some type of recessed lighting will also come with a rubber or foam gasket to help seal in the air from warm side to cold, negating the use of a traditional plastic boot.
Whatever the method used, maintaining a vapor barrier is in integral part of building heating efficiency and keeping a healthy air quality for the people that use the space.
Vapour Barrier Update
There have been some changes in the building code that now require the use of plastic boxes with built in vapor barriers to be used on the exterior walls. Personally I think this is bad as the metal boxes with a plastic vapor barriers are easy to remove when doing renovations and add more wiring. Now more than likely, you will have to cut a large hole around a plastic box if you need to remove the electrical box in a finished wall.
You are still "allowed" to use plastic vapor barriers, but it is now required that you frame around the box creating a tighter seal. This becomes a pain in the butt and would be time consuming.
Sometimes innovation in building code isn't really thought through as far as practicality. Renovations will now cause a lot of damage to the walls and the vapor barrier of the wall. Rules are rules though and they are expected to be followed.