Green Roofs are Growing
Walking south along Michigan Ave. from the Chicago River, a first-time visitor might take in the green vistas of Millenium Park sprawling eastward toward the great lake with no hint that the park itself is a green roof. It covers two garages and a commuter rail line, occupying close to 100 square meters in Chicago's East Loop district and taking in a great lawn, a garden of native Illinois plans, a music pavilion and water features. It's one of the largest vegetative green roofs in the world.
Around the globe, vegetative green roofs are sprouting. The Expo Zaragoza Empresarial Business Park in Spain, built for a 2008 sustainability exposition, features more than 43,000 square meters planted with grasses, perennials and aromatic plants. Building rooftops in the Village on False Creek in Vancouver, British Columbia, Canada, a LEED1 Platinum neighborhood, are carpeted with sedum. At the Frankfurt International Airport in Germany, landscaped areas blanket several buildings and total some 80,000 square meters.
Vegetative green roof designs fall into two general categories: those with sedums or drought-tolerant plants for extensive vegetative green roofs and complete landscape gardens for intensive vegetative green roofs. In either approach, the final product increases energy efficiency, reduces stormwater runoff and urban heat island effects, and provides habitat for birds and insects, and even leisure space - as with Millenium Park - for people. No matter the type of roof, the system comprises plants, growing media and layers for waterproofing, drainage and water retention. And that's where ASTM International standards come in.
ASTM International members began to develop vegetative green roof standards in the early 2000s in Subcommittee E06.71 on Sustainability (now reorganized as Committee E60 on Sustainability) with the creation of the green roof task group.
"There was a strong market need for substantive guidance. Also, there was a pretty good range of VGR technologies," says Dru Meadows, principal at theGreenTeam Inc., Tulsa, Okla., and E60 chairman. "It was a classic example of market need for performance standards and an excellent example of ASTM bringing together stakeholders to develop consensus documents."
Meadows says that the responsible task group looked to work on a comprehensive document, a "granddaddy" standard that would address the breadth of vegetative green roof considerations. The proposed guide, WK25385, Guide for Vegetative (Green) Roof Systems, now being balloted, has facilitated the task group's work on related standards that have been approved.
Completed standards include:
These standards, according to Meadows, have helped bring down early adopter costs and are referenced in the Whole Building Design Guide from the National Institute of Building Sciences. A vegetative green roof still often costs at least two times that of another commercial roof, and up to four times as much if paths or paved areas are added or if shrubs and trees are part of the plan, adding materials, installation and maintenance to the project. But, according to Michael Gibbons, chairman of the vegetative green roof task group and owner/president of Architectural Systems Inc., Dallas, Texas, the cost for a simple vegetative green roof might be recouped in energy savings in five years or fewer.
The granddaddy standard, WK25385, when approved, will fill the need of the practitioner wanting a complete approach to a vegetative green roof, or to answer the question as Gibbons puts it, "If I say I want a green roof, what's next?" WK25385 identifies the terminology, principles and concepts of a vegetative green roof consistent with E2432, Guide for General Principles of Sustainability Relative to Building, an E60 standard that covers concepts and building characteristics for general sustainability purposes.
Once WK25385 is published as a standard - it has recently been balloted by Subcommittee E60.01 on Buildings and Construction - green architects and others will find information about both intensive and extensive roof systems: plants, media, wind scour resistance, soil reinforcement, separation or filter layers, drain layers, irrigation, water retention layers, insulation, waterproofing/roofing membranes, protection layers and root penetration barriers.
Gibbons says that the draft standard is something of a checklist, but its sections provide discussion, for example, about such project parameters as maintenance, performance and longevity. Sections about planting media detail the different requirements for intensive systems and extensive systems as well as functional properties of the media, including nutrients, density and depth, organic matter and more.
The vegetative green roof task group has more standards development activities planned. Currently under way is a proposed standard on selecting waterproofing membranes for green roofs, which will list characteristics, materials and suggested performance requirements. The group will also be looking at possible vegetative green roof standards that address irrigation, fire, wind scour and roofs with steep slopes.
Where there are vegetative green roofs, right below the surface there may be an ASTM International standard.
1. LEED is Leadership in Energy and Environmental Design, a voluntary sustainable building program of the U.S. Green Building Council, Washington, D.C.