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Green Building News

A Deep-Energy Retrofit in Northwest Vermont

Upgrading a 35-year-old house: rigid foam for the walls, cellulose for the attic, new windows, new siding, and air-sealing work

A deep-energy retrofit of this three-bedroom house built in the early 1970s was recently completed by Pill-Maharam Architects and Conner & Buck Builders.
Image Credit: Pill-Maharam Architects
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A deep-energy retrofit of this three-bedroom house built in the early 1970s was recently completed by Pill-Maharam Architects and Conner & Buck Builders.
Image Credit: Pill-Maharam Architects
Insulating and air-sealing were among the top priorities. Four inches of polyisocyanurate rigid foam were added to the exterior walls, from the footing to the roof, architect David Pill says. The new siding and Loewen windows. The original windows and siding of the house, which has 2x4 construction and 2,400 sq. ft. of interior space, showed serious signs of age. Because the property did not have extensive landscaping, installing insulation on the exterior walls from the roof to the footing was relatively easy. The project’s keynote details as they applied to the west elevation, shown here, and elsewhere on the house: 1) existing wood siding to remain (to be covered over); 2) replace existing window and window casing; 3) remove existing window and casing for infill; 4) replace existing door; 5) existing door to remain; 6) existing foundation wall to remain; 7) remove existing surface-mounted conduit (to be buried); 8) remove existing light fixture; 10) remove deck assembly; 11) existing roof to remain. Exterior walls were brought to R-38 above grade.

The last time the three-bedroom home in Hinesburg, Vermont, saw extensive contractor attention was in the early 1970s, when the house was built. Recently, though, David Pill and his team at Pill-Maharam Architects, in Shelburne, Vermont, joined Conner & Buck Builders, of Bristol, to put the house through a deep-energy retrofit.

As Pill noted in an email to GBA, the house was “the perfect candidate” for the transformation.

Siding and windows were both “totally shot,” he said, and the modest landscaping close to the building gave the retrofit team easy access to the exterior walls, allowing the crew to perform air-sealing work and install 4 in. of rigid foam insulation from the roof to the footing. Loewen double-glazed windows – whose U-factors are not particularly low, but whose quality, Pill noted, is very high for the price – replaced all of the originals, and cellulose was blown into the attic.

Ready for winter – and summer

A new oil-fired boiler had recently been installed in the house, and tubing is now in place for a solar hot water system. In all, it took about nine months to complete the project, which brought to the walls of the building to R-38 above grade and R-20 below grade, and brought the roof to R-60. Pill says a blower-door test of the 2,400-sq.-ft. building, done before the drywall and finishes were in place, showed airflow of 500 cubic feet per minute at 50 Pascals of pressure difference.

He added that although he had not done any modeling, he estimates energy usage in the retrofitted house will be reduced by about 70%.

Pill and his wife, Hillary Maharam, are known to many GBA readers for designing their own energy efficient house, a 2,700-sq.-ft. building that was completed in 2007 and in 2009 won a $10,000 prize offered by the Northeast Sustainable Energy Association for the best net-zero-energy building in the Northeast. The house was sheathed with 1-in.-thick foil-faced polyiscyanurate, and equipped with a 10 kW Bergey wind turbine and a three-ton Econar ground-source heat pump. At the time, the house was one of only four in the U.S. to operate at net zero energy.


  1. steveoneil | | #1

    Cost? 9 months?
    I'm planning a DER on my home which is simliar in size. Could give the approximate cost of this work and comment on why it took 9 months? I'm hoping mine can be done in a much shorter time frame.

  2. jtlloyd | | #2

    9 months.....I wish
    I have been systematically knocking the energy usage down in my 1965 built home over the past 5 years. I am hoping in the next few years to reside the home and add 4" of foam. I am envious of the ones that could do a Deep Energy Retrofit all in one shot.

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