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Graywater Reuse to Irrigate a Living Wall at Bertschi School

Case Study by Chris van Daalen and Shawn Sanderson
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Graywater Reuse to Irrigate a Living Wall at Bertschi School
Heating, Ventilation & AC
Plumbing Systems
Greywater Reuse
Living Wall
City of Seattle
Dave Cantrell, Seattle King County Environmental Health Services
Bertschi School
KMD Architects
Skanska USA Builders
Living Building Challenge Certification v2.0 (All 20 Imperatives) See below for full list


The Bertschi School Living Science wing is an award-winning building located in the Capitol Hill neighborhood of Seattle, completed in 2011, which includes a small classroom, science lab and ethnobotanical garden.  It was the first building certified under the Living Building Challenge V2.0, considered the most stringent green building certification in the world. Among other deep green features, the project reuses greywater from handwashing sinks to irrigate an interior living wall. This helped the project achieve “Net Zero Water” as defined by the Living Building Challenge, i.e. a building that collects, treats and infiltrates all water used on the site.  To meet state and local code requirements, the greywater system had to have a conventional overflow connection to the city sewer but under normal operation, no water is sent down these pipes.

Permitting Process

To get a permit for on-site greywater reuse, King County Public Health required the installation of a conventional overflow to the city sewer to comply with the Uniform Plumbing Code and Seattle Municipal Code 21.16.040.   The Washington State greywater code WAC 246-274 also requires that the system is connected to city sewer even if the connection is not used; and limits the amount of water to be used. Installation of the conventional overflow to the city sewer satisfied all of these code requirements.


Code RequirementCompliance Path
Seattle Municipal Code 21.16.040 Required connection to City sewer for overflow drainage was permitted and installed
WAC 51-56-1600 Chapter 16—Alternate water sources for nonpotable applications. Requires greywater to be used for irrigation to be in compliance with local health department regulations and other rules as required by Authority having jurisdiction.
Chapter 246-274 WAC Greywater reuse for seasonal subsurface irrigation WA State Adopted Greywater code, allows greywater use up to 3500 gallons / day for subsurface irrigation only

Project Description

To help meet the LBC's "Net Zero Water" imperative the project incorporates a greywater system to irrigate a living wall within the classroom.  Potable water flows from the rainwater cistern or City connection to the classroom sinks, used primarily for handwashing.  Greywater drains from the sinks and into a tank in the cabinets below the sinks, an Aqua2 Use greywater system.  When the tank is full, or at least once every 24 hours the water is pumped to the living wall through a subsurface drip irrigation network.  The plants and soil of the living wall take up the greywater, releasing water vapor into the air through evapotranspiration.  Moist vapor from the plants is vented through the building's ventilation system and any water not absorbed by the plants is cycled back through the system and onto the wall again until all of the water has been used.

According to Seattle Municipal Code, adopted from Uniform Plumbing Code Chapters 301.3, a system within the range of a municipal sewer that is serving a commercial or public building must have a conventional overflow to the city sewer system. The Bertschi School does not plan to expel any waste or greywater into the Seattle Sewer system; rather, it will be treated and reused on site, but in order to meet regulation the conventional overflow has been installed.

In keeping with The Bertschi School's active learning environment, the Science Wing provides a living classroom and laboratory for students to learn first-hand about scarce resources such as clean water and air, and to see real solutions for protecting and conserving those resources.  In this case, graywater irrigates a living wall so that zero "waste" water flows to the City sewer.  Instead, students are taught to limit their water consumption to only the amount of water which the living wall can be expected to absorb and evapotranspire.

Design/Build Process

The Living Science Wing of the Bertschi school was the first “Living Building” in Washington state, a new addition to the school campus that also contains the first LEED Gold certified building on an independent school campus in the Pacific NW (completed 2007).  It was designed through an intense collaboration between Bertschi students and staff, and KMD Architects’ Restorative Design Collective.  The team interviewed the students to find out what they wanted in their classroom, and heard: "an indoor river, a bamboo fountain to relieve stress, and green house where something’s always growing". Architects, landscape architects, engineers, and other consultants paired these requests with the rigorous standards of the Living Building Challenge v 2.0 (LBC) to design a 1,425 sq ft science classroom building on a 3380 sq ft site with an ethnobotanical garden.

Resources & Supporting Documentation:

Full List of Certifications and Awards


Project Contacts
Owner: Stan Richardson, Facility Manager The Bertschi School Designer: Chris Hellstern, Architect ZGF Architects (then KMD) Builder: Stacy Smedley, LEED® AP BD+C Skanska USA Building
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