Why so deep, vs a frost-protected warm foundation?
That isn't deep, Nick. The frost line in much of Vermont can be 3, or even 4,
feet below the surface mid-state. Any building that depends on a surface
covering being applied around the foundation every year or periodically renewed
will eventually fail. People get older and more feeble, move south during the
cold months, or do other silly things. In the long run, it is cheaper to build
properly to prevent buckling and water pipe freeze-ups. (You have to dig and
lay pipe down at least that far to be sure it won't freeze mid-winter anyway.)
I don't remember whether building codes require a foundation below the frost
line, but I wouldn't be surprised in the least if they did.
Also, don't forget that the depth of the frostline can depend on which side of
a mountain you build on. Build on the north side of a mountain or hill and you
have to expect the frost line to be deeper and the frost to remain in the
ground much longer than if you build on the south side. If the area is exposed
and windswept and not covered by an insulating blanket of snow, the frost will
go deeper yet.
It would lose less heat if it were underground. NREL says the average
yearly temp in Burlington is 44.6 F. The average daily Jan temp is 16.3.
The average daily min is 7.5. The record min is -30 F.
Nick, Burlington is the sport of the litter in Vermont. The entire state can be
covered with clouds and there is often a patch of blue sky over Burlington,
primarily because of orographic influence. As air rides up over the Green
Mountains and Adirondacks and becomes less dense, it can't hold as much
moisture, providing clouds and precipitation, mainly in the form of light snow
or rain. The Champlain basin is just large enough that the air riding back
down the mountains becomes able to hold the remaining moisture and the clouds
dry up momentarily. Studies indicate that Addison County, which is just south
of Burlington, receives something on the order of 100 more annual days of
sunshine than the central part of the state.
Burlington also sits lower in altitude than almost all of the state. That can
make a huge difference as well. As of today, the lake at Island Pond is
substantially frozen over. Lake Champlain at Burlington won't begin to freeze
for another few weeks, and some winters Champlain never freezes completely
over. See for yourself here:.
http://users.adelphia.net/~homepage/page6.html
Until it freezes over, that six mile wide lake has a large moderating influence
on the surface air temperatures in Burlington. On the years that it does
freeze, the air temperature drops dramatically. I know this as a personal fact
since I lived about 500 yards from the shore in Burlington for a few years.
As for those balmy temperatures in Burlington being representative of the sate,
I don't think so. The lowest recorded temperature in Vermont, -50°, was on
December 30, 1933 at Bloomfield, however, there are pockets where similar
temperatures are reached many years. Burlington's record low may be -30, but I
remember delivering many a newspaper on -30 degree days only 25 miles deeper
into the state.