# Two Part Spray foam in addition floor



## jklingel (Dec 21, 2008)

I would apply a layer of rigid foam to the bottom of the floor joists, taping and gooping the edges to air seal them. That will help the fg batts work better, as you will be deadening the air around them. They are pretty useless w/ air moving past them. Then, close in the skirting and put a vb on the ground (condition the crawl space). Buildingscience.com has info on this, as well as many threads here.


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## joecaption (Nov 30, 2011)

http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table


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## jklingel (Dec 21, 2008)

btw: If I understand what you said about "external vb", that will likely be a disaster. The vb will be cold and condense. VB's, if used, are always on the warm side.


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## bill01 (Apr 12, 2012)

Just a note even though this is a little late. If you want to use the foam as a vapor barrier first you must use close cell foam. Next you need to check with the manufacture as to how thick they recommend to use as a vapor barrier. It seems to vary from 1 1/2 inch to 2 inch but nobody seems to say why there is a variation.

As a side note spray foam is not a fun thing to install it sticks to everything you have to wear all kinds of protection, crawling under a mobile home and spraying in a tight space would only add to the discomfort level.


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## M3 Pete (May 10, 2011)

bill01 said:


> Just a note even though this is a little late. If you want to use the foam as a vapor barrier first you must use close cell foam. Next you need to check with the manufacture as to how thick they recommend to use as a vapor barrier. It seems to vary from 1 1/2 inch to 2 inch but nobody seems to say why there is a variation.
> 
> As a side note spray foam is not a fun thing to install it sticks to everything you have to wear all kinds of protection, crawling under a mobile home and spraying in a tight space would only add to the discomfort level.


I thought most of the expanding foams like Great Stuff are open cell. But Great Stuff claims otherwise:

http://building.dow.com/na/en/products/sealants/windowdoor.htm 

http://building.dow.com/na/en/products/sealants/biggapfiller.htm 

_Latex foams are typically "open cell" and, as a result, can take on water. In fact, the same properties that allow you to wash latex foam off your hands with water also mean that the cured foam can absorb water. This can cause wood rot or deterioration in areas where wet latex foam is next to wood, such as a window frame. In contrast, GREAT STUFF™ is a closed-cell foam. It forms a water-resistant outer skin when cured._

A similar product, Pur Fill, also claims to be closed cell
http://www.todol.com/pdfs/purfillnf12_tech.pdf

Both of these would be a pain to try and uniformly cover a large area though. Not really designed for it.


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## Windows on Wash (Aug 30, 2011)

M3 Pete said:


> I thought most of the expanding foams like Great Stuff are open cell. But Great Stuff claims otherwise:
> 
> http://building.dow.com/na/en/products/sealants/windowdoor.htm
> 
> ...


Most can foams are closed cell and some of the large gap and crack filler ones are open.

Window and door foams are closed cell.

I agree with the other recommendations to use rigid foam and go that route.


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## Gary in WA (Mar 11, 2009)

Here is the link others have described: NO vinyl if using foil-faced f.b.; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Thickness depends on *your location* to prevent the dew-point from happening inside the cavity....

Gary


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