# Rigid Foam Under Rat Slab



## tomdor (Jul 27, 2011)

Okay, so I've searched the web and searched through this forum and can't find the answer to one question I have. 

I will be pouring a rat slab into my crawl space to prevent the persistent buggers from tunneling under my footing. I also plan to make this a conditioned crawl.

Should I pour the rat slab over rigid foam? Would it make a difference? I'm in climate zone 4c (Seattle)?

Thanks!


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## Windows on Wash (Aug 30, 2011)

Why kind of rigid foam?

I can't hurt.


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## Gary in WA (Mar 11, 2009)

http://www.house-energy.com/Insulation/Slab-Insulation.htm

http://www.wrcc.dri.edu/cgi-bin/cliGCStH.pl?watac1

Gary
PS. install 6mill poly under the whole slab first...


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## tomdor (Jul 27, 2011)

Happy New Year and thanks for the great info in the links! 

I was planning on using XPS but do you know if I can use R-Matte Plus ISO?

Thanks


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## Windows on Wash (Aug 30, 2011)

Use XPS under the slabs. 

ISOs are moisture sensitive.


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## Gary in WA (Mar 11, 2009)

The foil-facing is good IF there is a space, but not with a slab over it.... Just don't puncture the foil with rocks or pea gravel (in the concrete mix), hmm.....; http://www.inspectapedia.com/Energy/Insulation_Polyisocyanurate_Slab.htm

Or it can/will absorb 7 times more water in the test as XPS; http://commercial.owenscorning.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf

Gary


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## tomdor (Jul 27, 2011)

hmm yeah...my experience with the foil is that if often gets a small puncture if you look at it the wrong way. 

Thanks for the add'l info


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