Park Passive

Designed by NK Architects

Details

Green Features

Park Passive meets the rigorous Passive House standard. There were a number of other green features in the house, but Passivhaus is the only one for which I was responsible.

Lessons Learned

As with any innovative project, there was a steep learning curve.

We had three major surprises after the permit drawings were issued:

I had to reduce the TFA (Treated Floor Area, by which the energy budget for a Passivhaus is determined) by ~200 square feet because NK's schematic design drawings (on which we based our TFA take-off) did not show a second floor void over the kitchen, and I hadn't gone back to re-check the TFA until we got the final permit drawings. Voids are not counted as part of the TFA. That reduced our energy budget by about 10%.

The lowered SHGC (solar heat gain coefficient) of tempered low-iron glass combined with the need to use a lower-performing Intus window frame wherever NK had mulled doors with windows (which I had advised against), decreased the performance of the house by another 10%. This was not apparent until we got the final window proposal from Intus, and I noticed that all of the windows did not have the U-value I was expecting. This information was not, at the time, listed on Intus's website, nor common knowledge in the Passivhaus community. (I believe Bronwyn Barry, formerly the rep for Pazen Windows, was the only person in the United States who had encountered this issue prior to this.)

When the permit set was issued and I got the structural drawings I discovered (to my horror, I must admit) that the house was not advanced framed (which I had suggested in our initial Passivhaus charrette.) That is, it was designed with the framing 16" on center instead of 24" on center. (I've used advanced framing on every one of my projects since 1995.) Advanced framing was not possible structurally, according to the structural engineer, due to the complexity of the design. The increase in framing factor (a number entered into PHPP to reflect the amount of wood in the wall vs the amount of insulation) created another performance hit of close to 10%.

Keep in mind that ten per cent of the energy that a Passivhaus uses for heating is a very small number, since our target, 4.75 kBtu/SF/year, is right around 10% of the heating energy of a house built to code. Nevertheless, each of these discoveries, made successively between the point the house was submitted to City of Seattle for permit review and the start of construction, required a new run of PHPP, finding new design measures acceptable to the architects to get the performance of the house back to Passivhaus levels, and subsquent new revisions by NK of their construction drawings. In the rush to complete the process so that windows could be ordered and construction could begin I did not get prior authorization from Cascade Built for the extra work required, and so I was not paid for that extra work, which amounted to about half of my time on the project.

The small site combined with the Passivhaus-typical wall assembly caused one major headache during construction. The wall assembly (applied TJIs over a structural 2x6 wall) is designed to have the dense-pack insulation in the exterior TJI layer blown in from outside. However, on this site there is less than two feet from the south wall of the house to the south property line, making access from the outside almost impossible. On a larger site with typical setbacks Cascade Built could have tented the entire house to make blowing in of the insulation easier and to keep the house dry during its winter construction in Seattle. Or, they could have tented the other three sides and the top, and a different insulation technique could have been used on the almost inaccessible south side. As it was, Cascade Built drilled over 500 holes in the air barrier, dried the structure out from the inside with blowers, filled the walls with insulation, used a thermal imaging camera to find insulation voids, and sealed all 500 holes again.

Gladly, all of us involved in the project will be able to take these lessons forward and apply them in our next Passivhaus projects! And I hope you will too.

Credits

Certified Passive House Consultant: Rob Harrison AIA

THERM modeling: Bronwyn Barry, One Sky Homes

Passive House Construction Consultant: Dan Whitmore, Hammer and Hand

Architects: Marie Ljuboevic and Lauren MacCunney, NK Architects

Developer/Contractor: Sloan Ritchie, CascadeBuilt

Passive House Certification and additional THERM modeling: Bob Ryan, Lindsey Noctor, Passive House Academy

Blower Door Testing: Tadashi Shiga, Evergreen Certified

Contractor: Cascade Built

Categories		Featured, New Construction, Passive House
Location		Madison Park, Seattle
Date		2013

Description

I was the Passive House consultant on Park Passive. That is, I guided the designers, NK Architects, on the means to reach Passivhaus levels of performance with their design. Park Passive is the first certified Passive House in Seattle. Dan Whitmore’s Courtland Place Passive House, and Joe Giampietro’s Mini-B Passive House (since moved to Clearwater Commons in Bothell), lay well-deserved claim to being the first and second Passive House projects built in Seattle, but neither has yet been certified as meeting the Passive House standard. Technically I’m sure they both qualify.

As the Passive House consultant on the project:

I met with the architects, builder and structural consultant for an initial charrette, introducing the concepts of Passivhaus and suggesting design and technical strategies they could use that would make meeting Passivhaus easier and less expensive.
I suggested windows that met Passivhaus performance and the owner’s cost goals.
I did the initial layout of the ventilation system and hot water system and suggested manufacturers for the equipment.
I specified the types of appliances to use (for example induction cooktop, recirculating range hood, condensing dryer), and suggested specific brands to look at.
I proposed the assemblies (the layers of materials, membranes and insulation from inside to out) for each of the many floor, wall, and roof conditions of the house, with the amounts of insulation required in each.
I ran the PHPP (Passive House Planning Package) software multiple times during the design phase to confirm we were meeting our performance goals, and suggested changes to the design when we weren’t.
Finally, I coordinated getting the required Passive House documentation to our certifiers, Passive House Academy, that allowed them to evaluate compliance with the Passivhaus standard and certify the house according to the protocols of the international Passive House Institute.

Here is an example of how a Passivhaus consultant can interact with a designer: NK Architects’s first pass at the design showed a 4′ wide x 20′ high window in the north-facing stair bay. Since moving to an even thicker external layer of insulation (say 11 7/8″ TJIs outboard of the 2×6 structural wall instead of 9 1/4″ TJIs) would have meant losing floor area on the tiny site, and we were already using the highest performance glass offered by Intus (U-0.105, SHGC 0.62), the only avenue to optimizing the performance left was to add south glazing and reduce north glazing. I proposed and as you can see NK Architects executed my idea of chamferring a set of deep-set punched windows instead of the tall fixed window on the bay, using CFC-free polyiso to maintain a decent average R-value in the assembly.

This was a project of firsts. It was Cascade Built’s and NK Architects’ first Passive House, and the first Passive House on which I was doing Passive House consulting rather than acting as the prime architect. It would be safe to say it was a learning experience for all–and that’s a good thing, as we will all be able to carry this experience forward into our next projects. I find that Passive House projects are collaborative works of the entire Passive House community, much like early green architecture projects were collaborations of that community. Many Passive House colleagues contributed to the success of this project, and I believe in giving credit where credit is due: Bronwyn Barry did THERM analysis and Dan Whitmore provided consultation to Cascade Built on construction techniques as the house was being built. I also received great feedback and advice from members of the Passive House Northwest Google Group, including Adam Cohen, Graham Wright, and Dylan Lamar. Geoff Briggs in my office translated NK’s 2D AutoCAD documents into ArchiCAD BIM, to facilitate the take-offs necessary for PHPP.

The project was certified according to the standards and protocols of PHI (the international Passive House Institute). The actual certification work was done by Bob Ryan and Lindsey Noctor at the Passive House Academy. At this point the performance standards for PHI and PHIUS are the same, although the protocols for certification are slightly different.

NK Architects did a great job in maximizing the building volume available on the tiny 1,980 SF site, deftly and completely filling the entire zoning envelope in order to accomodate the owners’ program. Doing so required complicated massing, which is not conducive to Passive House in a number of ways, including the additional thermal bridging and surface area it created, and necessitating standard 16″ on center framing rather than the advanced 24″ on center advanced framing I had suggested at the initial charrette. At the extremely low levels of energy use of Passivhaus, that meant a performance hit of almost 10% that then had to be made up in other ways. The front of the house (shown in the photos) faces north, and it is shaded by trees east and west, and by a tall house immediately to the south, limiting the solar gain available through the windows. The architects’ decisions to cantilever the second floor by a foot, and to include a 14′ wide by 8′ high lift and glide door on the north side of the house which required a massive steel beam, created thermal bridges that could have been avoided with different design choices. Those design features and site constraints meant that we needed more insulation, higher performance windows, more efficient equipment, and more south glazing and less north glazing than we would have otherwise, but the fact we were able to achieve Passivhaus with this high-design project suggests that there is no excuse for not doing Passivhaus on every project, everywhere.

The house has been featured in several articles in print and online, among them:

Green Building Advisor: A Contemporary Passivhaus in Seattle

New York Times: Passive House: Sealed for Freshness

Treehugger.com: “Passive House is a Team Sport”

AIA.org: 2014 Housing Awards

Park Passive

Designed by NK Architects

Details

Lessons Learned

Description

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