Home>Discussions>INSULATION & HVAC>Insulate Crawlspace: Perimeter Walls or Floor or Both?
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ZLA
Insulate Crawlspace: Perimeter Walls or Floor or Both?

We own a 30 year old multi-level house where the main level above a crawlspace is cold in the winter. Part of this is due to its cathedral ceiling but I feel some part is due to a lack of insulation for the crawlspace.

After reading several articles and posts, I am still trying to determine if I need to insulate the floors, the perimeter walls or both. The dirt crawlspace is unvented, unheated (except for heat leakage from the floor above and the forced air ducts running under the floor. It's about a 4' high space over dirt which I believe is generally dry though I think it can get damp or moist but not wet during heavy rains.

I'm not as concerned about what materials to use or how to do it but rather on what needs insulation.

Thank you in advance.

canuk
Re: Insulate Crawlspace: Perimeter Walls or Floor or Both?

The entire underside of the floor should be insulated ... especially since the heating ducts are located there as well.

This will make a huge difference to the comfort in the living space also there will likely be some reduction in your heating bills since the ducts are loosing heat to the crawl space.

Hope this helps.:)

ZLA
Re: Insulate Crawlspace: Perimeter Walls or Floor or Both?

Thank you for the reponse, Canuk. If I insulate the floors, do I need to insulate the perimeter walls also or just the between joist cavities above the foundation walls?

I assume I should also put down a 6 mil plastic layer on the dirt as well, correct?

canuk
Re: Insulate Crawlspace: Perimeter Walls or Floor or Both?

The floor of the living space is the critical area for proper insulating to prevent heat loss.

As for the perimeter of the crawl space ... there's mixed camps on this subject.

Since the idea in this case is to have insulation to prevent heat loss .... the crawl space is not a heated space .... in theory there is no concern for heat loss.

The comparison is made to things like having a room above an uninsulated garage.
The garage would be similar to the crawl space.
Another example would be a room that is cantilevered into open air or over a porch ... as long as the floor of the room is well and properly insulated there shouldn't be an issue.

Would it hurt to insulate the perimeter walls ? ... No.

Some municipalities require insulating the perimeter walls and some don't ... similarly ... some municipalities require venting a crawl space and some don't.

Covering the dirt floor of the crawl space with a continuous 6 mil plastic is a good thing to do.

Hope this helps.:)

ZLA
Re: Insulate Crawlspace: Perimeter Walls or Floor or Both?

Thank you so much Canuk. That helps wonderfully. I really appreciated your point by point answer to every one of my questions. It's so rare to have such a detailed answer to online questions that I truly thank you for going the extra mile.

Once again, my thanks.

Re: Insulate Crawlspace: Perimeter Walls or Floor or Both?

This crawl has leaking duct work and the wall is uninsulated-you don't realize how much heat loss there is.One picture is above the floor and one is under.

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