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
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.