Big green building news out of Seattle this week: With a blower door test meter reading of 0.58 ACH50, the first built-on-spec passive house project in the Pacific Northwest has officially achieved Passivhaus-dom.
I first mentioned the project — “Unit 13” —  just a little over a year ago in my post on Columbia Station, Dwell Development’s 15-home green micro-community within the mixed-use, public transit-oriented Rainer Vista development in southeast Seattle’s Columbia City neighborhood.
Built as part of Phase 4 of Columbia Station, the three-bedroom, 2.5 bath home incorporates the standard passive house building/design elements — a super-insulated building envelope, high-performance windows, airtight construction, the reduction/elimination of thermal bridging, heat recovery ventilation, and a reliance on passive heat sources — to help it reach a staggering 90 percent efficiency. Or, in the words of third-party verifier Tadashi Shiga of Evergreen Certified, living in the 2,000 square foot abode is “like getting a 90 percent off coupon in the mail for utility bills”.
Remarks Dwell Development principal Anthony Maschmedt who worked alongside a team consisting of Shiga, project architect Julian Weber, Seattle-based passive house consulting/design firm Brute Force Collaborative, and others on bringing the spec home to super-efficient life:
"We made the commitment to building a Passivhaus on spec because we believe so strongly in creating energy efficient homes and keeping them affordable. It’s paying off now ... the home pre-sold in November 2012, in the early framing stage of the project."  
I should note that the first blower door test performed on the Columbia Station Passive House in January wasn’t quite as successful. Dwell Development market strategist Debra Bouchegnies explains:
A few weeks ago we ran our first blower door test at our Passive House in Columbia City, with results indicating we had to look for leaks and holes to patch and come back and redo the test. Our first test, resulting in a reading of 1.62 ACH50, meant that there were 1.62 air changes per hour (or ACH) under 50 pascals of pressure. A pascal, by the way, is a unit of pressure measurement which is used more commonly now — rather than ‘pounds per square inch.’
In order to qualify as a Passive House the house must meet a standard of passing the blower door test of a .6 ACH at 50 Pa. That means when under pressure of 50 pascals, the home must have only .6 air changes per hour, or better. Well today we ran our follow up blower door test and achieved a .58 ACH50! Measures that were taken to bring us to success included re-installing windows, reapplying the exterior waterproof sealant, and taping or sealing tiny holes where joints meet.
Bouchegnies goes on to explain that a conventional home changes air about 7 times per hour under 50 pascals of pressure while Energy Star standards allow for 5 or 6 ACH.
The Columbia Station Passive House, a remarkable infill project that now has official bragging rights as a true Passivhaus, was recently joined by a rather high-profile neighbor: The House of the Immediate Future, a Miller Hull Partnership-design prefab-hybrid Habitat for Humanity home partially erected by a team of volunteers near the base of the Space Needle and then dissassembled and relocated to Columbia Station earlier this year.
You can learn more about the Columbia Station Passive House and view floor plans over at the Dwell Development website. The team has also released a series of seven short videos documenting the blower door test at the home. I’ve embedded the final video below. 

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