Sloped Design

Garden Roof with a Slant in Bellevue, Washington

by Marc Dodson, editor


From Western Roofing May/Jun ’15


A green or vegetated roof is always impressive, but the Bellevue Youth Theatre in Bellevue, Washington, with its sloped vegetated roof is a real head-turner. The facility is dedicated to providing theatre arts opportunities for all young people, regardless of income or ability. The theatre stages quality productions that are both entertaining and socially relevant. Jointly sponsored by the City of Bellevue and Bellevue Public Schools, the Bellevue Youth Theatre blends the youthful enthusiasm of children with the wisdom of seniors. People with disabilities, families, and senior citizens are encouraged to participate.

Becker Architects, Bellevue, Washington, designed The Bellevue Youth Theatre as an environmental sculpture in the park. The new theater structure was inserted into the existing sloped hillside of the park. This simple, economical building structure provided the base for the Garden Roof Assembly® by American Hydrotech, Inc., based in Chicago, Illinois. The living roof was seamlessly integrated into the surrounding park lawn providing an occupiable space over the theater as well as sound attenuation, storm water management, and visual continuity of the park. The lawn rolls up and over the building structure with openings at the entry plaza, offices, and outdoor stage. A terraced lawn gently slopes down to the outdoor stage area with seating for up to 600 patrons. The roof is comprised of 8″ thick concrete pre-tensioned hollow core planks, which are covered with a 3″ concrete topping.

According to Richard Hayden, American Hydrotech’s Garden Roof Assembly manager, “Architects and owners are no longer limited to designing for flat green roof applications. The Garden Roof Assembly can now conform to irregular slopes and undulating roofs. For roof slopes greater than 3:12 and with soil depths of 3 1/2″ and up, a GardNet® soil confinement system must be utilized. The Garden Roof Assembly on the Bellevue Youth Theatre is particularly impressive because of its sloped design. A sloped garden roof can be designed for visibility and viewing from a wider range of locations, not just standing on the roof. American Hydrotech has come up with a system, which makes it possible for extensive and limited intensive applications on slopes ranging from 2:12 up to 12:12, provided the appropriate measures are taken to cope with the shear forces and soil retention.”

Bob Becker, Becker Architects, stated, “35,000 sq.ft. of Monolithic Membrane 6125® was applied to the foundation. MM6125, a hot applied rubberized asphalt, is one component, conforms to all surface irregularities, and bonds to an acceptable substrate, such as concrete, steel, wood, etc. It is completely monolithic, there are no seams, and no VOC restrictions. In addition, 13,000 sq.ft. of Garden Roof Assembly was installed using the GardNet soil confinement system, allowing the visibility to be an architectural design feature. The growing media is a non-compacted substrate mix, with amendments incorporated uniformly to provide a well-draining, fertile medium for vigorous long-term plant root growth. The surface layer has a growing medium containing a mat of turf grass and grass roots.”

Six architectural light trumpets extend upward from the lawn of the green roof. They are fabricated from steel framing and sheathed with painted aluminum rain screen panels. These light trumpets, have a wide base, which narrows toward skylight apertures at the top that provide natural light into the support spaces around the main theater space. In addition, mechanical exhaust ducts, exhaust fan ducts, and plumbing roof vents reach up through three of these trumpets. While the other three trumpets house fresh air supply ducts for the support space mechanical equipment. Louvers for these ducts are behind the rain screen panels, completely hidden from view in the park.

The exhaust dome, which extends upward from the center of the green roof, will be used to exhaust unwanted hot air rather than using energy to mechanically cool the hot air and re-circulate it back into the theater. The rain screen panels for this dome are similar to the panels on the light trumpets, hiding the exhaust louvers from view.

Bellevue Youth Theatre’s mission is to provide opportunities in the performing arts for all young people, regardless of income or ability, and allow them to perform before a live audience. Acting is not the only area open to participants either. There are opportunities for people interested in set design and construction, lighting design and operation, costuming or stage crew. At the same time, the theatre provides the community with quality productions, which are both entertaining and socially relevant for the entire family. The completed theatre is now functional, serving the Bellevue community, and offers an impressive and unique sloped garden roof design that is the pride of the city.