Vapour Barrier Placement

There appears to be no information as to the correct placement for the vapour barrier. I do not know if it is not required where some of you live but I have not seen it in drawings and pictures of double wall construction. My understanding is that the barrier should be 33% into the wall from the heated side as this is the dew point of the insulation in the wall. Houses in this area of Canada built in this manner do require a vapour barrier. Walls are generally 12" inside to outside plus your brick or siding. Interior wall is framed in place first with the vapour barrier on the outside and draped over basement header. Next is 1/2" ply t&g. The vapour barrier is then flat on the floor surface and draped out and down over the header. The outside wall is then framed with a top plate of 3/4" ply 12" wide to cover the top of the double walls. If a second story is used then double beads of caulking are used under the base of the next upstairs interior wall. Insulation is installed in the usual manner except that the space between the interior and exterior wall where it is installed horizontally. The exterior wall is then finished in 1/2" ply. This makes for a very substantial house. Cost of framing and insulation is about 1/3 more.
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