# Rigid Foam in Crawl Space between Joists?



## Windows on Wash (Aug 30, 2011)

To different approaches that you are referencing. 

What is on the floor above?

You should be able to insulate between and cover the joists with a rigid foam.


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## Bhava (Nov 11, 2012)

Windows on Wash said:


> To different approaches that you are referencing.
> 
> What is on the floor above?
> 
> You should be able to insulate between and cover the joists with a rigid foam.


After looking at my post, I think I might have been a little vague. I meant to say that the insulation I want to install between the joists, is rigid-foam--not fiberglass. 

My question is, do I install the rigid-foam at the top of the joists, to the vapor barrier which is under the plywood sub-floor, or to the bottom of the joists?

Also, as an afterthought, I was wondering, instead of just rigid-foam between (and at the top of) the joists, would it be acceptable to install it at the bottom of the joists, with the addition of fiberglass above it, and below the sub-floor?,

I'm asking about this extra protection because the temperatures here can drop to as low as -30C (-20F)!

Again, thanks very much for any help!


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## wewantutopia (Feb 28, 2012)

I think WoW was suggesting filling the area between the joists with fiberglass again then attach rigid foam to the bottom of the joists. This will stop the thermal bridging of the joists, protect the fiberglass from critters, and, if the foam is thick enough and seams are taped, act as a vapor barrier. Fiberglass and rigid will really increase the r-value. Cutting the rigid to fit snugly between joists is a real pain (trust me I know!).


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