Passivhaus in Chapel Hill: Page 3 of 3

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Traditional bungalow architecture
The traditional bungalow architecture of this home in Chapel Hill, North Carolina, belies its incredible energy efficiency and adherence to the strict principles of Passivhaus design.
15-inch-thick walls
The 15-inch-thick walls have an insulation value of R-42.
The home’s open floor plan
The home’s open floor plan allows for easy distribution of heating and cooling without ductwork.
Floating framed walls
The floating framed walls inside the concrete shell help minimize thermal bridging and heat transfer, and provide wall space for running plumbing and electrical.
4-inch-thick concrete floor
Stained and polished 4-inch-thick concrete floors provide thermal mass to moderate temperature swings and store heat from the sun.
The Seniors enjoy the sunny deck
The Seniors enjoy the sunny deck on the south side of the house.
Well-Insulated roof
Insulating roofs to Passivhaus standards can be challenging because of the high R-values required and the amount of space this takes. In this home, a 10-inch strip of 1.5-inch-thick foam board, which has been carefully incorporated into the trim pattern, beefs up R-values under the eaves.
Insulated roof (detail)
In this home, a 10-inch strip of 1.5-inch-thick foam board, which has been carefully incorporated into the trim pattern, beefs up R-values under the eaves.
Triple-pane, argon-filled windows
Triple-pane, argon-filled windows take up about 100 square feet of the south-facing wall.
An air-to-air heat exchanger
An air-to-air heat exchanger exhausts stale air and brings in fresh air, but keeps about 75% of the heat while doing so.
Air-source heat pump
The air-source heat pump delivers heat to the living room.
LED track lighting system
The high-efficiency LED track lighting system provides significant energy savings compared to conventional incandescent bulbs.
Efficient Washer
Super-efficient appliances save money, energy, and water.
Traditional bungalow architecture
15-inch-thick walls
The home’s open floor plan
Floating framed walls
4-inch-thick concrete floor
The Seniors enjoy the sunny deck
Well-Insulated roof
Insulated roof (detail)
Triple-pane, argon-filled windows
An air-to-air heat exchanger
Air-source heat pump
LED track lighting system
Efficient Washer

To qualify as a Passivhaus, buildings must have a tight building shell that allows no more than 0.6 air exchanges per hour at 50 pascals of air pressure. The heating load must be less than 4.75 kBtu per square foot per year (1.4 kWh/ft.2/yr.), and primary energy must be less than 38.1 kBtu per square foot per year (11.1 kWh/ft.2/yr.). Primary energy refers to all energy used for space and water heating, appliances, lighting, fans, pumps, etc. Different sources of energy have a different multiplier for their primary energy score. For example, purchased electricity has a high multiplier of 2.7 (each kWh of electricity consumed is multiplied by 2.7) to include generation and transmission losses; natural gas has a multiplier of 1.1; and grid-tied PV systems have a multiplier of 0.7. The last two requirements are verified by reviewing heating, gas, and other utility bills.

While the Seniors’ home is still in the process of becoming certified (a process that takes at least a year, since an entire cycle of heating and cooling, as well as overall energy use, must be analyzed), the house already has met the rigorous building standards. A backlog of applications appears to be slowing the process as PHIUS accommodates growing interest and incorporates the HERS rating system into its standards. These growing pains can only be a good thing as super-efficient building becomes a bona fide movement here in the United States.

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Stephen Hren is a builder and writer living in Durham, North Carolina. He is the author of Tales from the Sustainable Underground: A Wild Journey with People Who Care More About the Planet Than the Law (see www.earthonaut.net).

Anchorage Building • anchoragebuildingcorp.com

Passivhaus Institute • passivehouse.com

Passive House Institute U.S. • passivehouse.us

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