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Seattle Gets a Passivhaus Townhouse

The developer who built the first certified single-family home in the city tries his hand on a different kind of property

Posted on Apr 21 2015 by Scott Gibson

The Seattle developer who built the city's first single-family Passivhaus has completed construction of "View Haus 5," a five-unit townhouse project that includes one unit built to the Passivhaus standard.

It would be the first townhouse in the city to earn Passivhaus certification. The builder is Cascade Built, whose owner, Sloan Ritchie, built "Park Passive," a three-story home that was completed in 2013.

The townhouses were designed by b9 architects. Among the Passivhaus consultants who worked on the project were Mike Eliason of Brute Force Collaborative and Joe Giampietro of NK Architects (the company which designed the Park Passive project). The units range in size from 1,100 to 1,700 square feet and have either two or three bedrooms. Each townhouse is three stories and has two bathrooms.

Each of the units has a different look, but only one of them will be submitted for certification by the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute U.S.

“All units were built using Passive House techniques to achieve a significant reduction in energy use to heat and cool the house,” developers explained in an e-mail. “Passive House is an unknown for many buyers and as a result it’s difficult to secure the needed ROI to make a project like this financially feasible. This project is located on an urban lot in a dense city neighborhood and would have required each unit to be modeled separately, resulting in additional and prohibitive cost increases, so we modeled one unit to Passive House levels and used that same wall assembly for every unit.”

One of the two-bedroom units is listed for sale at $690,000 ($403 per square foot), similar in price to a slightly smaller non-Passivhaus two-bedroom nearby, which is on the market for $650,000.

Construction details

Here are the details as provided by Cascade Built:

  • Exterior walls: Wood-framed 2x6 walls are sheathed with OSB and insulated with blown-in fiberglass in the cavities plus 4 inches of Roxul mineral wool on the exterior (for a total of R-39).
  • Roof: Framed with 11 7/8-inch I-joists and insulated with blown-in fiberglass plus an additional R-15 of polyisocyanurate insulation (for a total of R-63).
  • Foundation: Stem walls for the concrete foundation and crawl space are insulated to R-20, and the floors are insulated to R-38.
  • Windows: Three of the townhouses have double-pane Zola windows; the solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. (glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. only) of these windows is 0.62, and the whole-window U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. is 0.21. The other two townhouses have triple-glazed Zola windows with a glazing-only SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.5 and a whole-window U-factor of 0.14.
  • Mechanicals: Heating and cooling is provided by ductless minisplit air-source heat pumps. All units have Zehnder Model CA 350 heat-recovery ventilators for whole-house ventilation.
  • Airtighness: The Passivhaus-certified unit had a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. at 0.5 air changes per hour at a pressure difference of 50 pascals (ach50). The other four units tested at approximately 1 ach50.
  • Domestic hot water: On-demand gas-fired water heaters.
  • Renewable energy systems: Units are pre-wired for photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. arrays and electric car charging.

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Image Credits:

  1. View Haus 5

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