Greening the Site: Design Options for Sustainability

A discussion of current trends in site sustainability techniques to improve the health of urban forests and stormwater quality, and provide design solutions if there is no room for trees
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Sponsored by Deep Root Partners, L.P., greenscreen®, IRONSMITH, SOIL RETENTION
Angela D. Dye, FASLA, LEED AP
Grate Systems for Republic Square
in Austin, TX

The approach of elevating pavement over soil was used as part of the recent restoration of Republic Square in Austin, Texas to meet new program requirements for a stage and performance space while ensuring the continued long term survival of historic trees. The Auction Oaks of Austin, Texas are particularly prized and cherished as an historic site and valued for their grand shade. The Austin Park Foundation in cooperation with the City of Austin Parks and Recreation Department worked to remove 5-1/2 feet of imported soil (300 cubic yards) from over the roots of the trees, placed there in a previous park redesign in the mid-1980s, which was literally smothering the trees.

Using entirely fund-raised and gifted monies for the park renovation effort, part of the design was to create a suspended grate system and custom tree grate around one of the trees in order to create more people space. Both a plaza, and a performance space and stage area, are elevated approximately 30 inches above the tree's original trunk flare. The design team specified a below-grade framing system topped with IPE wood decking along with a fabricated custom collar around the trunk. The collar needed to be tight so that no more than a one inch gap was left between the deck and trunk to maintain safety for people yet ensure no railing was necessary. A separate tree ring grate provides for an access portal to the grating system and can be modified as the tree grows in diameter. "This effort was a very innovative and creative solution to maximizing flexibility and use under the tree canopy without adversely impacting the soil or roots," says Daniel Woodroffe, Studio dwg, landscape architect for the project and former principal with the design firm TBG Partners, both of Austin. Not to fear, though, the health and well being of the tree is being carefully monitored by the Friends of Republic Square and by the Urban Forestry Council, who together with Bartlett Trees, conducts tests on soil, irrigation, and general tree vitality. Woodroffe credits the cooperative relationship between the Parks' Foundation Executive Director Charlie McCabe, as the client, and the Austin Parks and Recreation Department Director Marty Stump, as the owner, as being instrumental in accomplishing such a huge task.

A below-grade pavement system under construction and completed to save the Auction Oaks of Austin, Texas

Photo: IRONSMITH, INC

LEED® and SITESâ„¢ CREDITS

Grate Systems

Many manufacturers have ensured their products can be used to gain credit for using sustainable, recyclable, or traditional materials. For those projects pursuing Sustainable Sites and/or LEED points, check the recycled content of cast metal products. Some products are made from recycled metal, often with a high percentage of post-consumer recycled metals mostly from scrap vehicle parts, and they are 100 percent recyclable. Most steel products are made from standard structural steel shapes from leading steel producers, and may use as much as 75 percent recycled metal since steel itself is 100 percent recyclable. Check where the foundry for all castings are located in order to meet the 500-mile regional materials point for your region. Be sure to ask that all the tree grates are ADA-accessible and slip-resistant. With recent American Recovery and Reinvestment Act funding, you should also determine whether the product is Buy America-qualified; in some cases, local fabrication can be licensed through the manufacturer and may still meet this criteria.

Suspended Pavement and Structured Soils

Suspended pavement and engineered structured soil installations may contribute to both Stormwater Quality and Stormwater Quantity credits, Heat Island Effect (non-roof), and Water Efficient Landscaping. For stormwater management, ways to create soil volume or retention capability may be acceptable for credit. Also, creating the ability to grow large tree canopies that reduce the heat island effect, and specifying low water using trees will likely gain credit under Water Efficient Landscaping.

Drivable and Plantable Pavement

This approach to providing circulation and parking while also adding biomass may assist with credits for reducing the heat island effect. The infiltration capability contributes to Stormwater Management, while the product itself may use recycled material (fly ash) and be regionally produced.

Vertical Screens/Green Walls

Green walls can contribute to LEED® credits in Sustainable Sites, Water Efficiency, and potentially, Energy and Atmosphere. With Urban Heat Island (non-roof), green walls can shade heat-absorbing materials such as concrete and masonry that reradiate heat into the atmosphere. Water Efficiency (50 percent reduction) and Water Efficiency (no-potable/no irrigation) stormwater and grey water capture systems can be used to water green walls. For Innovative Wastewater Technologies, a method to use wastewater for green wall plantings has been designed. Green walls help shade buildings and help to reduce energy use. This could be a contributing factor in meeting a reduced energy load on buildings.

Thinking Holistically

As the Sustainable Sites Initiative gains steam, and begins to refine its Guidelines and Performance Benchmarks into a Reference Guide, keep in mind that these techniques and approaches present you with an array of choices to design with based on a project's program and design intent. A streetscape may benefit from tree grates, a below-grade grating system, suspended pavement or structured soil, or a combination, depending on the site conditions, design context, and project budget. Is there a need for a vegetated fire lane or a unique condition that warrants turf-filled parking spaces? What climate modification design feature may be required to shade a building, courtyard, walkway, or vegetated roof, to reduce heat gain or provide comfort and respite to people? Follow the progress of the SITES Pilot Projects to find out more about what works and what will work for you.

Angela D. Dye, FASLA, LEED AP is the owner of A DYE DESIGN, recently relocated to Telluride, Colorado. She is a Past President of ASLA.

Deep Root Partners, L.P.
SOIL RETENTION

 

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Originally published in GreenSource
Originally published in November 2010

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