To build a nature awareness center that did not disrupt the natural environment, the structure chosen was an earth-sheltered, earth-integrated concrete building heated by passive solar energy with electricity provided by a wind generator and hot water by solar collector panels. Five hundred cubic yards of concrete were used in the 6000-square-foot all-concrete building. Walls and floors were cast in place, but the roof was constructed of precast, prestressed hollow-core planks with a 2-inch thick, cast-in-place concrete topping.
Specifications called for 4000-psi concrete. With a combination of water-reducing admixtures, actual cylinder tests failed at 5600 psi. A troweled-on bentonite waterproofing was applied to the exterior walls and horizontal roof deck, followed by 4 inches of foamed polystyrene insulation. This gives an R-value for the insulated concrete walls of about 23; the R-value of the roof is 24. Earth cover on the roof ranges from 6 inches at the front parapet to 6 « feet at the skylight.
The net result of earth-sheltered construction, passive solar design, wind-generated power and solar heated water can only mean large energy savings for the nature center. The building gains heat through south windows, a greenhouse and a large central skylight, and it keeps this heat by closing off all these areas at night. After its first year in operation, the nature center required only five cords of wood to heat, and that came from the nature preserve itself.