Sustainable Land Development Today - October 2008 - (Page 12)

Cuttings are sprinkled by hand over the soil surface of the greenroof. get them to give us one of their largest grants last year,” Norton said. The next challenge was to come up with the remaining 75 percent of funding. Norton tapped into an experience he had two decades ago, when he was able to work with a utility company to build a new mechanical plant for the station. The arrangement allowed that utility to own the plant for the first six years, and pay for it through depreciation and shared operating costs. “In California, third-party ownerships are very popular because there are some very good tax incentives from the state,” said Norton, though such incentives are not on the books in Massachusetts. “However, you can get some federal tax credits and accelerated depreciation from the IRS, if you have a system that is large enough to make it worthwhile for an investor group to become interested.” An investment group in California, which was involved in such solar energy systems, agreed to back the project and initially own the array. “They had to take possession of it before we had an interconnect with the local utility. It had to pass all the scrutiny of an IRS audit,” Norton said. “They own it. They maintain it. They service it. We are just the host of the facility.” The financial arrangement spans 25 years, but the key component is that WGBH will buy back the array in seven years. “We lease it from them, pay them a pre-negotiated, set-amount per kilowatt hour, and we guarantee that we will use all of its power, which is not a problem,” he said. Putting it all Together The rooftops of the new WGBH complex span 25,000 square feet. Of that, approximately 4,000 square feet is covered with solar panels which are surrounded by a total of 5000 square feet of greenWater Systems Planning Road Design Watershed Analysis Environmental Assessments and more … roof. A 60mi. rubber roof membrane spans the entire roof surface. Portions of the roof structure had to be reinforced to accommodate the added weight load. The planting media for a greenroof is much lighter than natural soil, but still accounted for approximately 53 tons of additional weight. The effect of wind on the solar panels was also an issue to be addressed. “It’s not a tremendous factor, but you are adding something to the roof that the wind could conceivably get under, pick up and pull off,” Norton said. “We actually have two types of solar panels on our roofs. On the upper roof, which was not reinforced, the panels lie flat because of the concern of wind. On the lower roof, they are at a 10-degree angle. We could support them and secure them to the roof differently.” Both of these factors were primarily issues for the new connector roof. “It was designed just for snow load, so we had to deal with five-pounds per square foot of additional loading factor which also had to take the weight of the panels and the wind shear factor into account,” Norton said. The greenroof surrounds the solar array. It starts approximately a foot from the edge of the roof and covers another nine to ten feet to the perimeter of the array. Bordered on the outer edge by blocks and perforated edging, the soil is two to three inches deep. It is blanketed with cuttings of drought-resistant succulents. The bed is then covered with a water-permeable and biodegradable fabric similar to burlap, which keeps the cuttings in place as they establish themselves. “They will grow to be between three and four inches tall. We do not want to block off the solar panels,” Norton said. The greenroof system is patented by Philadelphia, Pennsylvania-based Roofscapes, which franchises it to local landscape companies, which do the installation. For the WGBH project, Apex Green Roofs did the work and will maintain it for two years as the greenroof gets established. “These succulent plants are very low maintenance. They don’t require a lot of irrigation. The plants are very hardy in the summer. It’s more like a wild field,” Norton said. “We actually do not have irrigation up there for them. You hate to pour water on a roof if you don’t have to.” Installed in May, the cuttings are taking hold and are expected to turn greener through the fall months. Architects wanted to make sure that the view of the roof was accessible for employees as well as visitors. Intermap’s affordable 3D maps are uniformly accurate and reliable. Call 1-877-837-7246 for details. www.Intermap.com SL1 Circle 110 • or www.SLDTonline.com/webcard 12 October 2008 Sustainable Land Development Today http://www.Intermap.com http://www.SLDTonline.com/webcard

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Sustainable Land Development Today - October 2008

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