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Old 10-31-2013, 07:36 PM   #1
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Foam Insulation


I'm having an addition built and will be using closed cell foam for insulation

I am wondering what to use between the 2 x 12 floor joists to prevent the foam from going into the crawl space

floor is 2' above grade

someone suggested using bubblewrap or vapor barrier plastic stapled between each joist bay
but not sure best way to mount or thickness of plastic etc

is there any other suggestions ?

the foam contractor says he has never encountered this issue before

Lew
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Old 10-31-2013, 08:06 PM   #2
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are you using rigid foam or spray foam. if your using rigid foam simply get a few cans of spray foam to use as adhesive for the rigid then spray around the perimeter of the final layer to stop any draft.. no plastic required. type 2 foam is a vapor barrier
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Old 10-31-2013, 08:16 PM   #3
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closed cell spray foam

if they spray between the joists there is nothing to "catch it" and prevent from filling the crawl space

what is best method to keep it between the joists ???

I need 4.5" of foam between joints for R30

Lew

Last edited by lewisbuttery; 10-31-2013 at 08:27 PM.
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Old 10-31-2013, 10:31 PM   #4
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The spray foam I've seen sets as soon as it hits the underside of the subflooring and sides of the joist, very little falls down.
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Old 10-31-2013, 11:23 PM   #5
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I live in the Buffalo NY area

the sub-floor is off and the spray foam is going down into the joist bays

something is needed to keep the foam in the bays

otherwise it will just fill the crawl space below the joists

the crawl space is only 2' tall from grade to top of sub floor

not roomy enough to spray from below

I think one method will be to nail 3/4 x 1 pt strips along the bottom inside edge of each 2 x12 then lay 3/4 pt plywood on those strips to create a bottom for each bay

the foam can then be sprayed on these bottoms

I think that will work better than stapling bubblewrap for bottoms

Lew
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Old 11-01-2013, 10:07 AM   #6
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I take it you want to spray from the top side.

you could use strips of building wrap (typar/tyvek) stapled to the sides of the joists. you'd have to figure out what your require R-values is in inches so you'd know where to place it.

just place the weather side down. good luck!
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Old 11-01-2013, 10:36 AM   #7
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Gary:

thanks, the Tyvek would probably work

the foam vendor called, different guy,

he understood and said that bubblewrap is what they use for
spraying from topside or knee wall etc

where a "catcher" is needed

I'll let me GC decide between Tyvek or bubblewrap

thanks

Lew
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Old 11-02-2013, 01:08 PM   #8
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Tyvek will work, either side out; it is not "one-way" vapor permeable (58 perms). The logo and stud markings are on the smooth side from manufacturing. The bubble is probably a true vapor barrier. Photo 6; http://www.buildingscience.com/docum...n-crawlspaces/ Notice air "open" to ventilation.

Gary
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Old 11-02-2013, 10:29 PM   #9
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if their spraying foam they can very easily spray from below and it will not fall out. it sticks to the underside of the sheathing.. they just cant do it all in one pass. we have it done on a regular basis with no issue. and im in a similar climate
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