The Natural Philosopher wrote:
o Careful insulation required, otherwise heating bills will skyrocket
as you try to heat up the surrounding earth.
The earth does have large thermal inertia, so to start of with,
moisture will condense on the walls like crazy, unless ventilation is
adequate. After lots of heat input, the walls (and floor, and roof)
will have heated up to a comfortable temperature. The problem then is
to avoid overheating (like the underground, as you say). A lot of this
is climate dependant - in a hot, dry, climate massive walls and sunken
homes are an advantage. In a cold, wet, climate, a layer of sodden
earth at between zero and 10 degrees centigrade against the walls of
your dwelling makes it No Fun At All. Hence, decent
isolation/insulation is required, otherwise you will be trying to heat
the groundwater. You'll be looking at needing cavity walls, floor and
ceiling - not a bad idea for drainage anyway - increasing construction
costs. You'll need to ensure the drainage does not get blocked,
otherwise the cavity will become a nice cold water jacket. Allowing for
reasonable access for this will start to get expensive. Most of the
water in the UK is hard water, so the drainage cavity will start to
fill up with limescale deposits - even more fun to get rid of.


You don't understand about insulation do you?

Apparently not. What specifically do you think I'm not grasping? I'm
willing to learn.

Sid