The non-profit organization Habitat For Humanity has built another super-efficient house, which has received the highest LEED rating, LEED Platinum for homes. The 1,340 square foot, 3 bedroom and 2 bathroom, 1.5-story single family home, called the Westford House, is located in Westford, Massachusetts. The house has an estimated savings of roughly 40% over a similar more traditional home, which come to an estimated $1295 per year. The additional initial investment for making this home so efficient was $10,000.

What is most interesting about Westford House is that it achieved the highest LEED certification without any of the typical renewable energy features such as solar panels or wind turbines. This allowed the construction costs of the home to be kept at a minimum. The total construction costs of the home came to $175,000, proving that building an energy efficient home does not need to be very expensive.

The rafter framed unvented attic of the house features R-66 roof insulation, which is made up of unfaced fiberglass batt insulation (R-40) in rafter bay with two 2” layers of foil- faced polyisocyanurate insulating sheathing (R-26) on top of roof sheathing. The wall was assembled using a 2×6 construction at 24” on center with a rating of R-45, which is the result of using unfaced fiberglass batt insulation (R- 19) in the wall cavity with two 2” layers foil-faced polyisocyanurate insulating sheathing (R-26) on outside face of stud. This type of wall construction also reduced the amount of lumber needed for construction by 40%. In both cases the joints were staggered and taped.

The house was fitted with double pane vinyl Low-E Argon filled Harvey Vicon double hung windows with an L-Fin adapter. The heating of the house is achieved via a 96% AFUE sealed combustion gas furnace with a MERV 13 ilter installed in conditioned space. The hot water is heated by an instant gas water heater. The ventilation of the house is achieved via a central fan, which is controlled with an Aprilaire controller. A Fantech energy recovery ventilator (ERV) was also installed. No cooling was installed in the house.

The builders fitted the house only with Energy Star rated appliances, while the Lighting is comprised of Energy Star CFLs. In the final blower door test performed Westford House air leakage was 2.1 square inches per 100 square feet of enclosure. In comparison, the maximum air leakage allowed is 2.5 square inches per 100 square feet of enclosure area.

Westford House currently serves as a prototype for building highly efficient and highly insulated homes that function well in cold climates. For this project Habitat for Humanity partnered up with the Building Science Corporation.