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Battle of the Damp Crawlspace


CKELLY's Avatar
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03-16-05, 01:24 PM   #1  
CKELLY
Battle of the Damp Crawlspace

Howdy,
I'm moving on the the next project in my 1880 brick hillside house. The crawlspace is wet, and will probably always be wet. The surface water uphill seeps in, then hits the bedrock and flows downhill under the rubble foundation. You can see bedrock throughout most of the crawlspace (and see a little water cascading down). Obviously I will do my best to divert, drain, and ventilate, but this is an insulation/vapor barrier question...

In this slightly wet crawlspace, would it be OK to install a vapor barrier on the bottom of the floor joists, to let any water flow on its way downhill, and also keep damp air from corrupting joists and subfloor? And, what about rigid foam (installed somehow) below the poly?

 
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03-16-05, 01:43 PM   #2  
That sounds bad I think Id go like we do if we have everything open under like a new room. Insulation in the joist paper up to the home a R 19 then put a cheap siding on the joist bottom . let the whole crawl way open to the out side .

ED

 
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03-16-05, 02:13 PM   #3  
CKELLY
Thanks for the reply Ed,
What did you mean by "cheap siding?"

 
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03-17-05, 01:23 PM   #4  
Just about any thing to close it up even just thin plywood. Think of it as just another outside wall is all. But let it all open under there not just vents in a crawl space big big vents.

ED

 
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03-17-05, 02:01 PM   #5  
CKELLY
Thanks for your help. That sounds good to me. BIG vents.

Here's a picture of my idea to keep moisture and termites away from the joists, and get some insulation:
http://home.earthlink.net/~chriskellydesign/crawl.gif

What do you think?

 
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03-17-05, 02:13 PM   #6  
Looked at the picture no no no. Think just like and out side wall in the floor. R19 insulation paper side up on top to the room and the siding on the bottom of the joist no V /B there at all. You could put what is called a house wrap there but no V/B.

And I mean big big vents all around it.

ED

 
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03-17-05, 02:44 PM   #7  
CKELLY
BIG vents all the way around won't be possible, so perhaps air inductor and exhaust fans with a humidistat??

 
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03-18-05, 12:10 PM   #8  
CKELLY
I'm sure there is a lot that I don't understand here, but, why not a vapor barrier? -OR- how about my previous scheme, with vents in the baseboards to let room air circulate through the floor joists. Like this:
http://home.earthlink.net/~chriskellydesign/crawl2.gif

Bear with me--this is how I learn. I like to know how things work, AND why they don't. Thanks Ed.

 
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03-18-05, 12:31 PM   #9  
CKELLY
What's this?
http://www.insul.net/prod_af_atab.html

I'm out of control.

 
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03-18-05, 01:05 PM   #10  
Went to a lot of their paper work never did find a R value. I see it as just a very good reflector for a hot water setup.

Might go to http://aboutsavingheat.com/crawlspace.

Now if you cant keep the water out of there then Id go as I said , make and think of the floor as an outside wall and let it all open under it.

ED

 
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03-18-05, 01:30 PM   #11  
CKELLY
I found some good stuff here too:
http://oee.nrcan.gc.ca/keep_heat_in/...tView=N&Text=N

Wouldn't you use a 4-mil sheet under the drywall (subfloor) of an exterior wall? I guess I'm concerned about condensation, and also about water vapor rising up through the floor. (I'm a pain in the butt, huh?)

 
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03-18-05, 05:53 PM   #12  
That is right .That is why I said put the paper side up to the floor or room side for a V/B. When we do this as a new room say after all the joist are set. we take one big sheet of 6 mil poly and put it down over the joist . Then plywood sub floor. will but a R19in the joist on the under side then the siding. No V/B on the bottom. Its just like a side wall of the home. You do have to vent the whole crawl space. Let it open all around.

ED

 
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03-19-05, 03:36 PM   #13  
CKELLY
Thanks Ed, I've got it now.

Venting this crawlspace will take a little creativity. I'm going to move over to the basements forum.

Thanks so much for your patience.

 
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