A cold-climate heating scheme that makes use of the sun and the earth
The “sun-earth connection’ makes this solar-heated house
the next step up the solar evolutionary ladder, claims its designer, Tom
Smith. The connection Smith refers to is the continuous air space
running from the peak of the south-facing sunroom down to the soil
beneath the house.
Intended for cold-winter climates, the design is noteworthy for its
simplicity. It does away with some of the solar design features that
have become well known in recent years: it has no superinsulation, no
additional thermal mass (like trombe walls, rock bins, or water
columns), no double-shell construction, and no extensive amount of
Running the length of the south side, the sunroom both heats and
insulates the rest of the two-year-old house. It collects heat through
a set of surprisingly small windows, equal in surface area to only 15
percent of the house’s total square footage. (Smith calculates that
15 percent is optimum for gaining heat by day without losing too much at
night.) A series of windows and doors opens the room to living quarters
in the two-story house.
The heat moves from the sunroom to interior spaces by natural
convection or with the aid of paddle fans, then stores in the mass of
the house itself. At night, with doors and windows closed, heat stays
On extremely cold nights, the earth below the crawl space contributes unexpected heat. Because the earth is protected by the
house, it remains a fairly stable 50| no matter what the outside
temperature drops to. If the air temperature in the sunroom drops below
50|, the heat in the earth begins to convect into the air. Warmer air
rises to the sunroom through spaces between the 2-by-6 decking.
Common-sense elements such as minimal windows on the heat-losing
north side, appropriate (R-30) insulation for the Lake Tahoe climate,
and an air-lock entry kept construction costs reasonable compared to
houses with superinsulation and additional storage mass. To reduce heat
loss, Smith insulated the exterior of the perimeter foundation; to keep
out moisture, he covered the crawl space and underside of the floor
joists beneath living spaces with a plastic vapor barrier.
Owners Beth and Barney Lovelace have a woodstove for back-up
heating. In the summer, they can draw cool air from the crawl space by
opening the top windows in the sunroom.
Photo: Crisp lines of shingled exterior accent south side of house.
Limiting amount of glass on this side keeps sunroom from overheating or
losing heat too fast. Sketch illustrates flow of heat
Photo: Wood-paneled sunroom has slight spaces between floorboards
to allow air movement from the crawl space below. Doors and windows on
right open to let heat pass into house