Hi,

I have a 50-year-old backsplit that has a large uninsulated crawlspace
under the living room and kitchen. The crawlspace has a concrete floor
and is about 4' high. It connects with the heated part of the basement
via a short door. It's not directly heated by a duct, but the
temperature never gets anywhere near zero.

In winters (which are pretty long in Ontario), the living room and
kitchen get very cold; the floor is extremely cold. My plan is to
insulate between the joists in order to keep the heat where it is
needed. I plan on running a duct into the crawlspace to keep pipes from
freezing.

My question is ... do I need a plastic vapour barrier? I thought so,
but a Government of Canada website on the topic says no. To quote:

"If the floor above the crawl space is already covered with an
impermeable material (e.g., linoleum or plywood), you already have a
vapour barrier where you want it. The solid materials of the floor can
serve as the air barrier, but be sure to locate and seal any air
leaks."

This is good news for me, because I don't know how I could lay strips
of barrier in the bays between the joists and make an airtight seal.
It's way easier just to stuff batts betwen the joists. But is this is a
mistake? If it matters, I'm using Roxul insulation -- unfaced and not
affected by moisture.

Thanks for any insights anyone may have.

Tom