August 8, 2005

Green Roof Moves Forward with Minor Changes
ASLA roof is set to contain six distinct green roof conditions.

At the beginning of this week’s conference call between the ASLA Green Roof Task Force and the design team charged with completing the roof, Michael Van Valkenburgh Inc.’s Chris Counts, ASLA, project manager and associate in charge of the project, joked that the team will take away from the ASLA green roof project “a lesson in HVAC placement, more than anything.” In fact, the heating and air-conditioning units on the ASLA roof—which have been shifted around the roof numerous times during the design process—resulted in yet another design change as the team heads toward drawing up construction documents for the roof.

Under the latest plan, the HVAC units serving the north side of the building, which were to be moved to a position behind the south mound, have been relocated to the northwest corner of the roof. This change will help reduce costs by cutting down on changes to the ductwork and will help the unit function better for the building. The change also means that a separate structure will be incorporated on the north wave of the green roof, allowing the HVAC unit to be placed under the wave while still providing access for service and repairs.

Click on the image above to download a .PDF of the latest ASLA green roof design.

A place for sitting, safety, and storage
In another minor change to the roof, a bench will be placed at the edge of the central platform. This seemingly innocuous addition actually provides three distinct design solutions for the roof. In addition to providing the obvious seating, it also acts as a safety measure, helping to prevent someone wearing heels from stepping onto the steel grating of the roof without realizing there is a surface change. The bench will also be hinged so it can store any tools needed to tend the roof.

As an added safety, the grating system has been raised to create a six-inch step up from the wooden observation deck. This will alert roof occupants to the surface change between the viewing platform and the steel grating that will cover the majority of the roof.

The sixth green roof area
Because the ASLA green roof is a demonstration project, it’s important that it include a wide variety of green roof areas. A new patch of extensive green roof that will not be covered by steel grating brings the number of different areas up to a solid half dozen. Here’s a breakdown of the green roof systems the ASLA roof will have:

These six variations of green roof will allow ASLA to show interested parties a wide range of green roof systems, as well as to monitor which solutions work well and which are more challenging. However, because of the excellent work of the design team, the roof “won’t look like a showroom of green roof solutions,” as one Task Force member put it.

One design element that will not be included on the ASLA green roof is an unplanted area that would allow passive planting on the roof, via birds and the wind. After much debate on this point over the past several months, the Task Force finally reached the conclusion that this element would not be included after David Yocca, ASLA, project principal at Conservation Design Forum, argued persuasively against it.

Yocca noted that having the volunteer area set amongst the planned elements could cause them to be polluted by what would eventually grow in the unplanned area. He added that this would be a particular problem if, as proposed, the unplanted area was placed above the pavilion. He also noted that, from an aesthetic point of view, the area above the pavilion would be one of the areas visible from the street and should make a strong statement. This would not be possible if passive planting were to be used in the area.

“What you’ll end up doing is shoehorning spontaneity into the roof,” Yocca concluded. “The idea of spontaneous vegetation is a worthy pursuit, but unfortunately, it just doesn’t work in this design.”

Research and monitoring
Finally, the Task Force and the design team discussed what kind of research and monitoring would take place on the green roof. While Yocca noted that traditional green roof research such as stormwater and heat island reduction were important for the demonstration, he added that a primary focus of the project should be making green roofs more mainstream and demonstrating that landscape architects play a central role in green roof design and construction.

Yocca proposed tracking the design and construction process to debunk the myth that only architects and engineers should be installing green roofs. He added that any research should address the biggest objection to green roof construction—short-term costs—and emphasize and track the long-term benefits. He also said that the struggle to relocate the HVAC units should be noted, arguing that if the building were designed from scratch to have a green roof, the team would not have faced those challenges.

“We’ll be on schedule”
Despite the design challenges posed by the HVAC units, Michael Van Valkenburgh, FASLA, pledged the project would remain on schedule, with construction to begin in mid-October. Counts added that the final construction documents were being drafted and could be made available to Task Force members who requested them. He added that the firm is in talks with construction and materials firms to work on the roof. Yocca said that CDF will also compile a specific plant plan for the various green roof elements and make recommendations as to what plants should be used.

Complete coverage of the ASLA Green Roof Project

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