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Old 02-29-12, 07:46 AM   #15
Apprentice EcoRenovator
Join Date: Oct 2010
Location: Simcoe County, Ontario, Canada
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The Ontario Building Code, which is virtually identical to every Provincial and Territorial code in Canada, requires a Vapour Barrier over every moisture permeable insulation product in exterior walls. A vapour Barrier has to be there in one form or another.

Most simpler installations consist of 6mil poly over fibreglass, mineral fibre, cellulose, and so on. These products are marketed under numerous names.

Where people are getting creative, and staying legal, is with the use of Closed Cell spray insulation. Closed cell insulation is considered an acceptable vapour barrier, in that no additional barrier needs to be installed. The Code allows the Vapour Barrier to be located up to 1/3 of the way into the insulation, as measured by R-value, from the warm side. This means that you can spray the stud cavities part way, install your wiring and plumbing, and finish with a thin layer of vapour permeable insulation and drywall. This approach can be varied by several diferent ideas, the wall can be strapped, or a second stud wall can be built.

Another product that can be used as a Vapour Barrier is closed cell rigid styrofoam board. Again, there are numerous names attached to these products. Insulation board can be installed on the inside, under your drywall. This requires extreme attention to the details, and every joint must be properly sealed, as per the manufacturers instructions.

Open cell spray insulations must be treated as vapour permeable, these products can actually become waterlogged if installed incorrectly.

And finally, beware of the possibility of accidentally installing a second vapour barrier. For instance, the example of the 1/3 rule where there is a layer of moisture permeable insulation overclosed cell spray. Avoid the temptation (if you are so inclined) to install a layer of 6mil poly, or foil backed drywall. You can trap moisture in between.

I am a firm believer in a properly installed vapour barrier. I do renovation and home repairs, so I often get to dig into walls and see what's happening in there. I price my work slightly higher when I suspect there is no, or a poorly installed vapour barrier. I know I will likely find mould, and people hate mould. In new construction, in my opinion, the proper installation of the vapour barrier is one of the steps that produces the highest returns on investment

Last edited by herlichka; 02-29-12 at 07:50 AM..
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