Growth Opportunities: Private Residence

Private Residence in Quilcene, Wash.
Green roof size: 3,200 square feet
Award recipient: Hadj Design (green roof designer) Project Team
Architect: Bosworth Hoedemaker
Growing Media: Swanson Bark & Wood Products
Overburden Installer: Solterra
Roofing Contractor: CRS
Structural Engineering: Swenson, Say, Faget

The Hood Canal project is a small-scale green roof on a west-facing coastal residence in Quilcene, Wash. Situated on the Quilcene Bay, which leads through the Juan de Fuca Strait to the Pacific, the project is an example of a small-scale project with an even smaller development impact.

The design strategy involved two priorities: aesthetically reflecting the pre-development plant environment and minimizing the impact of the development on the local wildlife. These overlapped to the extent that some local species that support the wildlife could work in the shallow media and under green roof microclimatic conditions. Where this was not possible, two tactics were used. One tactic was to select plants that mimicked the appearance of a species that were maladaptive to a roof environment, but supportive of a particular target animal species. Another was to support green roof conditions that encouraged species succession, and thus allow evolution over time toward better wildlife and plant species integration.

The design principle used was to provide a medium (ultimately composed of grey pumice, Bio-Stable compost, and phytonutrients) that was slightly higher in organics and fines than normally called for in roofs of such a depth, in hopes of encouraging evolved species development. Selected site species shared guild patterns with species that would not immediately work on the roof, but with soil biology evolution over time it was hoped that intermediate species would develop. Eventually, with the interaction of attracted wildlife and the plant and soil biology dynamics, the desire was to create an “evolutionary pressure” on the installed system. The roof is now home to a variety of local insects and birds.

The lower unplanted roof of the project was given driftwood elements and drain rock on top of drain mat. This served two functions. It reduced the uplift damage from the windward edge of the roof by setting the newly planted areas back from the edge and providing heavier ballast at the roof edge. Also, by using drain mat and wind-sun break elements as well as small promontories, this roof element extends the range of environments available to long-term plant development. All of these elements help to fit the Hood Canal project into its ecological surroundings, and ensures that the quality of the little stormwater that drains from the green roof is essentially the same as that which drains from the present undeveloped landscape.