Bob Peterson said:
Financially you break even if you spend 7-10 times the amount of annual
energy savings you get on the initial building cost (depending on interest
rates).
OTOH, if you want to live in such a home just cause you want to, that's a
lifestyle issue, and might well be worth the extra money to you.
Exactly - it's a payback issue, not a question of whether it "works" (in
isolation from expense). How practial it is in a particular area may
also be climate affected. You are less likely to have moisture/mold
problems in a desert/dry location than a moist/humid location; or, if
you build one in Georgia (or even New York, where I've experienced the
soaking wet floor of a basement apartment in summertime), you probably
still need an air conditioner (or dehumidifier at minimum) to keep the
hot wet outside air from drenching every cool surface inside your bermed
home during summer. In Utah, this is not likely to be a problem most
(all?) of the time. I don't know where Missouri falls on the humidity
spectrum.
When I looked at doing things here in Vermont, it came out much cheaper
to go with a lot of insulation above ground, using structural insulated
panels, than to go below ground with concrete. If you are going with the
foam/concrete/foam (which costs a lot more, here) for tornado or termite
resistance (not big issues here), I doubt it matters much whether it's
buried or not - on the other hand, burying would not hurt, if it didn't
run the cost up much.
You can run the numbers yourself, easily enough - Look up the NREL data
for the site closest to you to get average temperature data, and compare
the amount of energy used to heat/cool with an exposed wall of whatever
insulation level you'll use for an above-ground wall exposed to the
outside air, .vs. the amount used to heat/cool an undergound part of
wall exposed to (guesstimated averages, since a bermed wall is close to
the surface, not deep and steady) of 40F in winter and 65F in summer,
unless you have a local water department which keeps track of soil
temperatures at various depths who can provide you with real numbers to
use.
It's best to put this in proper prespective by modelling the whole house
in a speadsheet, so that you can see the overall effect of the bermed
(or non-bermed) wall on the entire energy use for the house. Windows,
doors, and ventilation make very large impacts on energy use when the
walls, floors, and ceilings are well insulated.
