100% all-electric with no combustion on site.

Renewable Energy System
8.1kW DC (36 225W Sunpower SPR-225-BLK solar panels + 36 individual Enphase microinverters). The system produced 8,939kWh during the 12-month documentation performance period.

Efficiency Measures
The Grocoffs’ renovation was achieved within the tight restrictions of the Secretary of Interior Standards for Historic Preservation. In keeping with these guidelines, they wanted to preserve the heritage, story of place and the beauty of the home without expanding the footprint. Therefore, they did not consider changing the structure or layout of the walls or windows. In addition, when the Grocoffs purchased their historic home, it already; had good solar orientation; eaves that provide summer shade for the second floor windows; a natural passive stack effect as a result of operable basement and attic windows; and large south-facing windows. These features were restored to their original functionality. Practically speaking, there were minimal improvements that could be made to the home’s thermal envelope. To achieve Net Zero Energy, attention was focused on optimizing energy use in the home through the introduction of efficient systems, appliances and controls.

Insulation and Sealing
Windows: The original windows are single-pane assemblies with wood framing. To improve the energy efficiency of the house, a wood window repair expert restored and weather-stripped the original sashes and hardware. Trapp low-e storm windows were added to the exterior. Air Changes per Hour @ 50 Pa (ACH50) were reduced from 15.70 ACH50 before the window restoration to 4.75 ACH50 after restoration and installation of exterior storm windows.

Wall Insulation Retrofit: On the exterior, the asbestos siding, installed in 1947, was removed to reveal the original wood clapboard siding. Two rows of clapboard were carefully removed. Holes were drilled through the wood lathe to allow for filling the above-grade balloon-frame walls with R-13 dense-pack blown cellulose insulation. The clapboards were replaced and the original exterior wood was restored and painted. Limited by the 2x4 width of the original framing, the walls achieve a value of only R-15 including the plaster walls and exterior wood clapboard.

Basement: The basement foundation walls are made of cut stone block and is are partially below grade. The rim joist cavity was filled with spray foam. However,though the stone foundation walls were left uninsulated. The basement is partially conditioned and used for laundry and storage.

Attic: The attic was converted from an uninsulated, poorly-ventilated space (vented with gable windows) to a cathedralized, unventilated space using open cell Demilec Sealection 500 spray foam, achieving approximately R-29. EcoSmart Insulated cellular shades are used on the interior of the windows.

The Michigan State Historic Preservation Office first denied the request for historic preservation tax benefits. They based their decision on the use of spray foam on the underside of the roof deck of the attic. The denial was reversed on appeal. The appeals officer determined that the since the foam was open-cell foam it was reversible. They stated that the “adoption of “new” technologies is problematic because of the possibility of irreparable damage or complete destruction to elements of a historic resource’s fabric that are irreplaceable.” However, they determined that it was demonstrated that after considering all forms of insulation, “that the use of open cell spray foam was the most appropriate choice for insulation of the Property in that it provides the best performance for contemporary use while maintaining the historic character of the Property.”

Photovoltaic Array
The Ann Arbor Historic District Commission voted unanimously to approve a thirty-six-panel solar array to cover the south-facing section of the roof from edge to edge. The Commission determined “that the proposed solar panels do not destroy, obscure, diminish, or damage character- defining features of the house, and are easily removable and reversible.” Even though the panels would be visible from the street and sidewalk, they said it was more “desirable to cover the entire roof surface of this house with panels since the panels and the roof color don’t match exactly. Covering more of the roof may be less conspicuous than covering a patch that will contrast with the roof.”

Lessons Learned
Using improperly installed flexible duct work for return air and the energy recovery ventilator dramatically reduced performance. Hard pipe does not cost significantly more and ensures proper flow rate.