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Crawl space foundation

I am considering a crawl space foundation for a new addition. The main reason I would like to go with the crawl space foundation is due to costs. One option I have is to install a concrete floor or not install one. Just wondering the pros and cons of the concrete floor. What are the moisture, radon and mold levels without the concrete floor? What does everyone recommend? The options I guess would be to install the concrete floor or leave it dirt and cover with a 6mil vapor barrier and insulation. Any info would be appreciated. Thanks.

Timothy Miller
Re: Crawl space foundation

Howdy one item to consider is the groundwater/ soils type you have. Another is the norm in your area. Alternative is to install 2 to 4" of foam an not vent but super insulate the crawlspace and add a 10 mil vapor barrier. An why not spend slightly more an have a basement instead of a crawlspace.

Why any crawl space? slab on grade is less expensive again one can super insulate below the slab. An if the room is with a southern exposure then use the slab as a heat sink an take advantage of passive solar heating. Colored concrete floor makes the slab even more attractive...

Re: Crawl space foundation

Thanks for the info Tim.

I have considered the full basement. It is an additional $1000. but I think it may be worth it. No slab since we have to go down 4' for the frost line.

Re: Crawl space foundation

irregardless of the cost and desirablility of basement, etc., most codes I've read recognize both poly and concrete as a 'vapor barrier' in a crawl space. PROPERLY INSTALLED a poly on the floor will be fine and I would suspect cheaper than concrete. If you're concerned or it'll be tall enough for storage, opt for a thicker poly like a 10 or 20 mil.
If used for storage, remember it's still vented, so humidity comes in from outside and could foster fungi growth on cardboard, etc.

Re: Crawl space foundation

I would recommend at least a slab with 2" of extruded insulation and insulate the walls to to make it part of the conditioned basement.
For an extra $1,000 I would probably go for a full basement. Crawlspace storage can be handy, but a basement is better. If radon is an issue, put in a radon mitigation system below the slab. Poly will do nothing to keep out radon and the poly alone has limited moisure control in my opinion even if it's allowed by code.

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