Rigid foam 2′ below grade? Zone 6, Central Colorado
user-987846
| Posted in Energy Efficiency and Durability on
Long time listener, first time advisor punching bag…..
I am in the probationary stages of becoming a rater, and am doing some work for Habitat. They have radiant heat in a 4″ slab, and have put 2″ foam 24″ below the slab, with gravel/dirt fill between. The foundation is ICF. There is no real passive solar enhancement to justify the added “mass” (minimal glazing on south side). Or maybe they do? I am worried that the mass under the slab will take quite a bit to bring up to ambient, and in fact act as a heat “suck”? Not looking for advice on how to put into rating, but definitely interested in what others think. Thanks.
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Replies
Well Bruce and Thorsten play with mass.... here's a start for you to search ...
Bruce Brownell Adirondack Alternate Energy http://www.aaepassivesolar.com/
I live near Bruce, I like the homes. He uses smaller mass lately. 12" of concrete.
Thorsten Chlupp is one hell of an interesting Alaskan innovator and builder. Search here and Google. One thread...
https://www.greenbuildingadvisor.com/community/forum/general-questions/19942/sunrise-home
http://www.arcticsun-llc.com/projects/the-sunset-roost-home/
Most will say your posted Habitat Home's mass is not worth the effort. What will be good and what will be bad... is debatable, and depends on the weather and the time of day and the use of the structure and the location of the home and the personalities of the homeowners..... endless I say... endless.
Greg,
Deciding to use your space-heating system to heat hundreds of pounds of dirt under your slab is a waste of energy. It's like building a big addition to your house, heating the addition with forced-air heating registers, and then nailing the access door shut so no one can visit the addition. What's the point of adding the heat if you can't visit?
The horizontal foam insulation should be installed directly under the slab, with only a sheet of polyethylene between the slab and the insulation. It's silly to pay to heat dirt.
Thanks Martin, kind of what I thought, but your analogy nails it home. Thanks again