While Aaron was in Seattle to join Mike for Passivhaus Consultant Training, methodhomes and infiniti real estate & development announced they were holding a pre-fab friendly competition for Seattle’s backyard cottage/DADU ordinance. We jumped at the chance to test our new found passivhaus chops (o.k., not that new, we’ve both been following passivhaus for a few years now) and decided to attempt a decent looking building that on an ideal site, would qualify for passivhaus or even Living Building Challenge (given the right amount of time….)
In order to achieve the passivhaus numbers, we loaded the south with windows for maximizing winter solar gain and minimized apertures to the north. Openings are strategically placed to allow views in all directions, thus eliminating any sense of claustrophobia for such a small abode. The other aspect we were shooting for was achieving passivhaus without having overly thick walls, which would negatively impact the net floor area on narrow lots. We initially toyed with utilizing cross laminated timber for the structure, but opted for a system that was closer to achieving LBC. Had we known that a local manufacturer would be available, we definitely would have preferred the CLT.
Walls: R-32.8 (U=.0305)
Roof: R-64.5 (U=.0155)
Slab: R-67.2 (U=.0149)
Triple pane window with high SHGC (0.55) and low-e coating, argon gas. The windows end up being a critical element to achieve passivhaus and while more expensive than double pane, optimize thermal comfort in the house and prevent critical loss of heat in winter.
The mechanical system is an HRV with ground source heat exchange, which could be laid directly under the building thereby mitigating ground disturbance.
Our intention was to make the submission fairly easy to fabricate and deliver to the site in either panels or a box module. The system could easily be adapted to a multitude of foundations: for a lighter touch on the landscape or sloping site, the unit could be set on auger cast piles. Alternatively, traditional footings and slab could be poured and the walls brought in as panels or a box for a pre-fab hybrid system.
The building is a simple 16’ wide module consisting of bath, kitchen, mechanical closet and living area that can be tailored to fit lots of varying width. A 13’ bedroom module can also be tacked onto the building. On wider lights, an office/guest bedroom could be added adjacent to the living area. This simple move allows the [PH]od to be brought in by truck and lifted directly into place.
We wanted to create a project that felt bright and open, yet could be fairly closed off from prying eyes. While the skylight along the northern wall results in a significant loss of BTUs, experiencing the continual shifting of daylight would be well worth it. The exterior windows on the south and west have operable screens to protect from the summer sun, and allows for privacy from the primary dwelling unit.
We really felt that having a green roof on this small, low building would offer a significant benefit to the neighbors – eliminating glare, providing a better view and maintaining natural habitat.
Per the PHPP (passivhaus planning package), with the addition of a 3.5kW photovoltaic array, [PH]od would be net zero.
With the addition of a 4.0kW photovoltaic array, [PH]od would be CO² neutral and a plusenergiehaus.
Method Homes has announced the winners of the challenge:
Jim Burton of Blip Design sweeps with best in show and most sustainable with his passivhaus backyard box.
Microhouse Smart Module takes most adaptable.
Gist Architecture’s BAUhouse takes runner-up best design execution.
Baldwin West Design’s Area 10 Biosphere remix takes most innovative.
And in an ironic twist, the best design execution goes to… Method Homes own Homb Modular?!? Maybe Derek Leavitt’s thoughts on open competitions are correct- outside of the EU, that is.