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crawl space insulating and venting...

Posted by Greg McDowell on October 27th, 2002 09:45 PM

I've read through quite a few of the previous posts on the subject and think I might be close to a solution. I'm still not sure of a couple things though...

First some relevant info...

* I live in a mid-1950's house in Lawrence, Kansas. It gets really cold in the winter and really hot and humid in the summer.
* Wood frame on concrete block foundation with a dirt crawl space. It has vents around the perimeter that I have been keeping open in the summer and closed in the winter (although I am rethinking that now).
* The gas water heater, furnace and AC are all in the house but use the crawlspace... the waterheater has a vent into the crawl space for make-up air, the furnace and AC supply and return ducts run through it as well.
* The only source of "water" is the window well entrance and, prior to a significant problem with the water heater T&P valve, the space was reasonably dry.
* There is evidence of condensation (musty smell, damaged HVAC insulation and the like).

Here's what I think I should do...

* Cover the ground and the foundation walls with a reinforced polyethelene liner to prevent moisture and water infiltration both from the ground and through the walls. It may be a little excessive since this board usually only suggests 6mil and this is, I believe, 16mil thick but I've been doing a lot of research and this seems to be my best bet.
* Insulate the walls and the edge of the floor with minimum R19 batt insulation. This is where I start to get a little confused... is my crawl space considered heated since the HVAC ducts run through the space? I think it is... at least until/if I seal the HVAC duct joints.
* Close the vents year round and cover the access point. Since it's really humid in the summers and really cold in the winter, it doesn't make a whole lot of sense to keep them open... ever. The only thing that I can think of to give me pause is the make-up air for the water heater that I know is coming from the crawl. I'm not sure if the make-up for the furnace is coming from there as well but I suspect it is. If I close off the crawl, I'm essentially closing off the make-up air supply... not a good thing.

Alternately I would just put plastic on the ground and insulate between the joists and insulate the plumbing and HVAC as I've read repeatedly in this forum. The question of whether or not the vents should be open may begin to become a mute point if I do this (in fact, now that I think about it, I keep the vents closed all winter and the water heater and furnace work fine). This sounds like a lot more work than what I'm thinking... and I'm not sure it's really that much better.

From what I've read on the net it really depends on whether the crawl space is conidtioned or not... what I can't seem to figure out is what qualifies as "conditioned?"

If Jay J and Insulator are still following these threads I'd love to hear what they have to say.

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