Passivhaus Spec Project

A Seattle developer has sold what he thinks is the first built-on-spec PassivhausA 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. building in Washington state. And the sale bodes well for builders specializing in these extremely efficient designs.

The 2,000-sq. ft. house, built on an infill lot at 3153 S. Oregon Street, is located in Seattle’s Columbia City area, in a cluster of 15 homes built by Dwell Development. Unit 13, as it’s called, was sold last November during the framing stage. A recent 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. confirmed that the house meets the Passivhaus airtightness standard of no more than 0.6 air changes per hour at 50 pascals of pressure (ach50).

Still under construction, the house has 14-inch-thick double-stud walls (R-45) that will be filled with cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.. It also has an R-70 roof and triple-pane windows manufactured by Intus. The water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. is Tremco EnviroDri. (For more specs, use the link for the Brute Force Collaborative website below.)

The incremental cost was only $35,000

Anthony Maschmedt, the developer, says he’s certain the house is the first spec Passivhaus in Washington State, and fairly certain it’s the first on an infill lot anywhere in the Pacific Northwest. The Columbia City area is on Seattle’s light-rail line and only a five-minute train ride from the city’s downtown.

The house sold for $535,000. Other houses in the Dwell development range in cost from the high $300,000s to the upper $400,000s, Maschmedt said. Features that should allow the house to become Passivhaus-certified at the close of construction added about $35,000 to the price tag.

Dwell builds between 15 and 20 homes per year. The company is building a total of 42 in Columbia City, including an additional two that will be built to the Passivhaus standard.

Unit 13 is the first Passivhaus building that Dwell has constructed. The design team included architect Julian Weber, Passivhaus consultant Brute Force Collaborative, and Tadashi Shiga, of Evergreen Certified.

The house sold quickly, and for a good price

What makes the project particularly encouraging to Maschmedt is that super-efficient homes are being snatched up by buyers even though they cost more than conventionally built homes. He says his houses typically are sold long before they’re finished.

“There’s a huge demand for it,” Maschmedt said. “Our homes are already selling for a premium compared to the competition.” He said another builder in the same community built a conventional, 1,500-sq. ft. home and had it on the market by 178 days before selling it for $305,000. Dwell built a house of the same size, had it on the market for “zero days,” and sold it for $420,000.

“When the economy went down and people were struggling to sell, our homes continued to sell because people who were buying in a down economy were doing their homework and wanted value,” he said.

Nothing made that clearer to Maschmedt than comparing his sales results with those of his fellow developer, someone he says is delivering a “good product.”

“We're selling ours with zero market days for $120,000 more than he’s selling his for,” he said. “That’s for the same size house on the same street. I would love to make Passive our new standard, and that’s what we’re trying to do — to make Passivhaus our standard spec,” Maschmedt said. “Every home we do. That’s my goal.”