vapour barrior in crawl space


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Old 01-26-07, 07:47 AM
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vapour barrior in crawl space

Hi, half of my very old basement is about 3 feet tall (at most) and sandy/dirty/rocky, so not very smooth. I want to insulate between the joists and vapour barrior it.

Is there a method for laying all the poly/vapourbarrior on such an unever surface? I fear once i get it on that i won't be able to navigate it for fear of tearing it loose? Can i get away with tuck-taping the pieces together, or is there a better/stronger product to use? As well, where do i attach the barrior when it hits the concret/stone foundation? Do i run it right up to the wood and nail in place somehow?

Perhaps i should do the insulation first - any thoughts on this?

Thanks a million for any insight you may have.
 
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Old 01-26-07, 10:24 AM
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put vapour barrier down on the ground covering the area, put insulation between the joist and take a breathable house wrap such as typar of tyvec and cover the joists and insulation to hold the insulation inbetween and allow it to breath so your subfloor doesnt rot from below. just lay the vapour barrier over the floor and tape the seems dont worry to much about the edges as its not going to stop moisture 100% it is just going to greatly reduge it you could calk the edges where it meets the concrete if you really wanted to
 
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Old 01-26-07, 12:28 PM
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Most tend to recommend overlapping 8 mil minimum polypropylene vapor retarder 6" and taping and running up inside foundation walls and taping to minimize vapor emissions.
 
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Old 01-26-07, 12:41 PM
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Thanks for the replies! I think i'll just get all the poly and get real dirty, and hope when i put the insulation in after that i don't destroy what i've laid down.

I was hoping for a magical foam or spray that instantly vapour barriers your basement... i guess i'm not so lucky
 
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Old 01-26-07, 01:33 PM
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Vapor barrier and insulation

Why would you want to put the plastic down then crawl over it to insulate? Why not get the insulation done,then put the plastic down? Have I missed something? Tom
 
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Old 01-26-07, 01:42 PM
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No you haven't missed anything - mabye i'll do it like that, its probably best... i do need to be able to crawl overtop of it, albeit not very often, so i guess i figured i doesn't matter which i do first.
 
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Old 01-26-07, 02:16 PM
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Wink

Dont put insulation up in the joist space no way, Close and seal all vents put a 2"or 3" insulation on the wall up to the joist. Put a R19 up in the joist space there on the sill plate all around then home. A 6 mil poly or better on the ground over lap it 2 ft and tape all seams.
Go read http://aboutsavingheat.com/crawlspace.html

 
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Old 01-26-07, 02:34 PM
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Ok, i think i understand, but i'm confused why i shouldn't insulate between the joists. Is there a reason? One person mention to do it, but put tyvec in so they don't rot... - i don't think i'd go to this trouble, especially considering there's wires and protrusions all over the place making this just plain cumbersome.

To be clear, you recommend R19 batt insulation in the joist space around the perimeter of the crawlspace. In between the joists throught the majority of the crawl space i just leave empty.
 
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Old 01-26-07, 02:47 PM
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Wink

Yes a R 19 just in the joist space up on the sill plate all around the home. A 2 or 3" on the walls can use a polyatyrene and glue it. This lets the ground and all work as a heat sink for the home.
 
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Old 01-26-07, 06:39 PM
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get a company to come in and put a dense spray foam ( when dry its rock hard) over the ground and up the walls, will cost alot more then vapor barrier but theres your magic solution =)

i wouldnt insulatte under the joist myself, i just misread and thought you were asking about doing so, just insulate on the inside of the rim joist at the ends of each joist space and around the foundation walls, least thats all i would do theres alot of different ways of doing this and alot of different opinions on the right and wrong way =)
 
 

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