PNA Vegetated Roof Workshop

What’s green, laid at an angle, and filled with Armeria maritime? The new Farmers’ Market shed at the Phinney Neighborhood Center.

I've been a member of the PNA for several years and frequently participate in PNA related events. One Saturday last March I joined with about 10 other community members for a work party that was disguised as a workshop. PNA Well Home Program Coordinator Michael Broili led the workshop, and started out with a presentation on integrated storm water management and the natural hydrological cycle of the planet. He told us about how, as a result of impervious surfaces in cities, towns and communities, this cycle has been broken and the natural environment suffers.

The workshop was a literally hands-on learning experience. The shed had been constructed, but the preparation of the roof had not. The intent was to provide a roof environment that would take water from a sink outside the shed through a sump pump system and divert it back up to the roof. The sump pump will be solar-powered.

One of Mike's points during his presentation was that each house in Seattle could provide all its greywater needs by capturing the runoff from rains that hit residential and commercial roofs and building sides. Greywater, he explained, is any water that has already been through one domestic usage, but is not sewage.

We learned how this can be done by diverting water from surfaces into a storage system, instead of into downspouts and sewers. Greywater storage systems can be above ground or below ground, and capacity can range from a few gallons to thousands. The stored water can then be used in a variety of way, from watering in the yard to laundry to flushing toilets.

During the workshop, we students were actively engaged in the development of the vegetated roof. A conveyer belt was used to move pea gravel, compost and pumice from the parking lot onto the roof of the shed. we laid a membrane layer between the pea gravel and the other materials, and laid PVC to distribute the greywater. And finally, we transplanted various plants (including the Armeria maritime) to establish themselves and benefit from the closed loop of water reclamation and distribution.

As I read more and more about how water and water rights are becoming increasingly politicized, this workshop educated me and the others who took part about the historic role of water in natural ecosystems, and how those of us who live in the city can recreate a natural hydrological cycle in their own homes.