Vapour Barrier in semi-heated Crawlspace?

[Thomas Nickerson]

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

[m Ransley]

A vapor barrier wont help, a cheaper way to keep pipes from freezing would be to use electric pipe tape with a thermostat and insulate the pipes well.

[tbasc]

You might get better results sealing & insulating the outer walls of the crawl space and allowing conditioned air into the crawl space. TB

[Joseph Meehan]

[e-mail] wrote: ..

I agree.

[Thomas Nickerson]

This is probably a stupid question, but do you mean the outside of the outside walls, or the inside (ie in the crawlspace)?

Thanks

TN

Joseph Meehan wrote:

[terry]

Why do you mention 'freezing pipes'. The OP says that 'It never gets anywhere near zero'. His worry is the cold floor and heat loss down through it to a basically unheated space.

Since it's Ontario, Canada. (most of the world uses metric now) that's most likely 'Zero' Celsius/Centigrade. In other words it "Never gets anywhere near 32 F".

[flansp78]

He is talking about the inside of the outside walls, the 4' concrete walls. If the walls are not studded, then you can insulate the floor but without a vapor barrier.