On 19 May 2006 00:52:08 -0700, wrote:

Hi

I'm renovating the basement of an old house in Victoria, BC. The
climate here is typical Northwest. It rains a lot, but rarely does it
get below freezing.

The building code in this area says I should put vapor barrier on the
external walls between the drywall and the insulation. This is to
prevent in-house moisture from penetrating through the drwall and
insulation and condensing against the cold external walls. It's the
same building code across Canada.

My carpenter says however, that this code is relevant in climates like
Alberta where it gets to -10 and stays there for months on end, but
that for climates like BC where it hardly ever gets below freezing it
does more harm than good. His recommendation is that I not use vapor
barrier on the external walls and simply drywall right over the
insualtion. According to him, in temperate humid climates like British
Columbia, vapor barrier seals the moisture in the walls and causes more
wood rot and mold than without it.

(He does, however, recommend putting vapor barrier up against the
foundation (~ 2 feet) BEFORE the insulation and then drywalling. That,
he says, is to prevent the outside ground water moisture from coming in
through porous concrete and into the walls.)

What is your guys' opinion? Is he correct? Would you vapor barrier the
external walls between the insulation and drwall in humid climates that
rarely get below freezing?

I'd use a spray-on close-celled foam as both insulation and vapor
barrier. You get no condensation against the sheathing because
there's no way for air to carry water there, and you get no
condensation against the vapor barrier, because the "exposed"
surface isn't cold.