Location: Weston, Mass.
Certification: Energy Star
Cost: $160 per square foot
Builder: Van Tassell Construction, Nashua, N.H.
Architect: HDS Architecture, Cambridge, Mass.
Developer: Weston Affordable Housing Foundation, Weston

The goal of the WAHFI two-family project was to demonstrate that comfortable, healthy housing could be offered at an affordable price. Residents, who pay about $1,400 per month in rent, earn less than 80% of the Boston metropolitan mean income, says architect Keith Gross.

The two connected townhomes were funded by the town of Weston with the stipulation that they would be extremely energy efficient, so planners looked to passive solar design, solar hot water, and a tight building envelope to achieve low energy consumption at cost-effective prices.

Built on a wooded vacant lot, the structure was oriented to optimize solar gain and, with limited tree clearing, allowed for full exposure of passive windows and active collectors. The building was placed away from the street on a knoll to gain full day exposure and for better natural ventilation for passive cooling. With open-cell spray foam insulation in the walls (R-27) and attic (R-50), ZIP System exterior sheathing, and triple-glazed U-0.22 windows, the house achieved a HERS rating of 51.

Active solar water heating meets up to 80% of residents’ water heating needs. Heating and cooling is provided by a 44,600-BTU gas furnace and a 13-SEER air conditioner with two zones controlled by digital setback thermostats. Air-to-air heat exchangers recover 65% of energy in replacement air that is ducted directly into the return air duct. All ductwork was insulated and sealed.

Other sustainable features:
--triple-glazed windows
--Rheem tankless instantaneous wall pack direct-vent gas water heater that brings solar preheated water up to usable temperature
--Energy Star lighting and appliances
--prototype passive solar window system

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