Petworth Rowhouse Received a Net-Zero Rating
Washington-based builder Tanya Topolewski recently completed the rehab of a 90-year-old rowhouse in the Petworth neighborhood of Washington DC at 411 Varnum Street. The four bedroom and 3.5 bathroom rowhouse was rebuilt from the ground up with the aim of achieving net zero status. The builders are also seeking the LEED Platinum certification for the house.
The final design went through 15 alterations before the right mix of energy efficiency was settled upon. The east-west position of the house was a hindrance, but the roof was fitted with the maximum number of solar panels that it can hold, which are designed to provide the energy for the entire house. The solar panels were all installed at the maximum 25-degree tilt, since a greater angle would have been a wind hazard. On the final audit, the house received a 0 score on the HERS index. However, the auditor warned that whether the solar panels will produce sufficient energy to keep the house at net-zero will depend on the energy usage habits of the new owner.
All exterior walls of the house were insulated to between R25 to R35, which was achieved through the use of dense pack cellulose or dense pack cellulose and polyiso board. Since the HVAC systems design has a considerable impact on energy efficiency, the air handler was placed inside the building envelope. All except one duct are also placed inside the envelope. All of these ducts are in inside spaces, except for the lines in the attic and those lines are buried under a minimum of 10 inches of insulation.
To ensure maximum sealing, low expansion spray foam was used around the doors and windows, while regular expansion spray foam was used to seal the penetrations to the exterior, floor to floor penetrations, and behind band joists. In addition to that, caulk was used to further seal all the framing seams, cracks, joints, corners and sill plates. The drywall was glued to the studs and joists, while the exterior rigid board was overlapped and tape sealed.
The house was fitted with a 15 SEER/8.7 HSPF high efficiency heat pump system, making in 20% more efficient than the minimum required 13 SEER. Furthermore, the house’s HSPF is 8.7, which falls into most the efficient heat pumps range of between 8 to 10. The attic of the rowhouse if also insulated to minimum R60 with blow in cellulose at a depth of 16-20 inches.
The house was also fitted with Energy Star appliances and low-flow fixtures to maximize water efficiency. The windows and doors installed have ratings of SHGC .3 or better and U-factor .3 or better.
During the reconstruction, many items, such as door, window and base trim, interior doors and interior door hardware (handles, mortise locks, decorative plates, hinges and keys), vintage lighting, bath fixtures, framing lumber including studs, 2×6, 2×8, 2×10 and larger and hardwood flooring were removed, cleaned, stored and reused in the final construction.
The costs of the green elements of the house came to $50,000, which includes $25,000 for the solar panels, $10,000 for the energy recovery ventilator, heat pump, hot water heater, windows and insulation, and $15,000 to meet the requirements of the LEED Platinum certification. The house recently sold for $725,000 to Florence Petizon.
