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Old 04-17-17, 08:32 AM   #1
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Default Insulation Guys - Tyvex on joists in crawl spaces?

We have an older ('30s) frame house with a crawl space over dirt. Poly plastic vapor barrier over the dirt. About 2 ft crawl space clearance. Wood floors on 16" center joists with unfaced R19 fiberglas batts between the joists held up with spring rod spanners.
My problem is that the house is balloon framed (common at least on the East coast til the 50s) which means the interior and exterior wall studding sits in the same framing as the joists which in turn means that the studs all go up thru the wood floor - so a million spots for air from the crawl space to leak up thru the unfaced insulation and then thru the many stud penetrations into the walls etc and even slowly thru the plank wood subfloor and oak strip main floor. Really chilly when the wind is up! AC Hacker is right - you're wasting time and $ with insulation if you haven't stopped air leaks.
Temps here are up to a muggy 95 or even 100F in summer and maybe down to 20s regularly in winter occasionally into single digits almost, rarely below 0 Fahrinheit. Crawl is vented in summer, closed in winter.
My first thought was to pull out the insulation and caulk or foam arounf each stud, etc penetration but God what a lot of work and still some leakage thru the floor seams!
Then considered the new grey spray foam to fill the joist alleys but didn't know if it allowed vapor to pass thru or even if that was needed with the foam? Moisture condensation in crawl spaces is a sizable problem here in the Southeast - i've seen crawl spaces which had glass insulation with vapor barriors on bottom side - they had trapped moisture til they sagged and fell to the ground - not pretty and can rot joists.
Also didn't know if i could do it myself and baulked at the per sq ft price if i couldn't!
So i have bought a hundred ft of some 3 ft wide Tyvex clone from Hdepo and plan on covering the bottoms of a couple of the joist alleys with it under the fiberglass as a test.
Spent a long time looking at contractor sites and opinions are both do and don't - and the DuPont site skirts the question really.
My thinking is that it will allow vapor to pass but block most air movement and is relatively easy and inexpensive.
Anyone done this or seen it done? Or have a good argument?

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Old 04-17-17, 09:35 PM   #2
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Default

I would go have a look at buildingscience.com. If I remember correctly they have a section on crawlspaces.

https://buildingscience.com/document...ace-insulation

https://buildingscience.com/document...in-crawlspaces

hope these help
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Old 04-18-17, 03:44 PM   #3
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Wow - thanks! That may be the best explanation of basement moisture movement I've read yet.
Now I have to read it again to be sure I'm with them!

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