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I have a client that wants to do a "modified" clean space crawl space. The space is dry and in fairly good condition. There is no fiberglass between floor joists (first time I have seen this without clean space, I bet the builder ran out of money).

It all boils down to this. I am going to put a r8-r10 board on the inside crawl space block walls (all vents are sealed). I read that this should then be covered with a vapor barrier. Can I use a foil faced board and would that act as the vapor barrier over the foam board or do I need to be more traditional and hang a 6mil sheet from the sill board and seal that to the vapor barrier on the ground?

Thanks

Coffeeguy.......
 

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R-8 to R-10 is not enough around here for a crawl space, that would be against code. Where are you located? What side does the vapor barrier go on in your area? And why does he care if the crawl space is clean? Does he plan on living under there?
 

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If this is a heated space, treat it the same as a bsmt.

I don't know how cold it gets where you are, but here if I use 2" styrofoam, no VB. Less that 2" and they require one.

I would not use one, seal all the seams, and DO NOT insulate the ceiling of the crawl space.

If this is an unheated space, seperate from the rest of the house you need to vent it, provide access, and insulate the ceiling.

Sounds like you have the first senario.
 

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i wouldn't open a vent in the ducts...if there is no insulation there now, i'd assume that the ducts are not insulated or airsealed either...and even so, the air will make its way around through plumbing penetrations and what not...you want it conditioned, but you don't want it at the same temperature as the living room, you know...so if you open a vent in the ducts, my opinion is the air will be a little to free to flow...
 
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