Frost Protected Shallow Foundation without radiant heat
kennebecwoodworks
| Posted in Green Building Techniques on
I am in the process of designing a home in Maine. Its roughly 1500 sq ft ranch style home with a slab on grade, double stud wall with 11.25 inches of dense pack cellulose and 18inches of loose fill in a vented attic. I have been contemplating the heating system and have been thinking about radiant but it seems like that may be overkill, and somewhat expensive. I was planning on a diamond polished concrete floor for the interior, so I was wondering with 4inches of rigid foam under the slab will the concrete be cold most of the time if using say a minisplit unit or even a woodstove?
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Replies
You're talking about 4" of foam under the entire slab, right? If so, then it will be cool, but not cold. The slab surface should be pretty close to room temperature....maybe a little cooler at the slab edge, depending on your slab edge detail. Having said that, 68F concrete doesn't feel the same to bare feet as 68F wood or 68F shag carpet.
Side note - please do not use XPS foam under the slab - https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-global-warming-impact-insulation ....unless perhaps it's recovered from another jobsite - http://www.insulationdepot.com/
You might want to get in touch with the folks at GO Logic in Belfast. They build with FBSF frequently, and Alan Gibson wrote a piece last year on the subject for JLC - http://www.jlconline.com/cgi-bin/jlconline.storefront/4e9f723001ffb6eb27190a323cb406aa/Product/View/1004sup
Mark,
Your slab will be warm enough. The real question is, do you like walking around on a concrete floor? Or do you and the rest of your family prefer a wood floor or carpeting?
If you conclude that you aren't quite ready to live on a concrete floor, you can install wood flooring over a slab.
Even if you installed PEX tubing in the slab, the heating system wouldn't be running that often, so your slab (even if the slab temeperature was 68 degrees) would still feel cool most of the time.