Ed Ritchie 2015-07-22 17:34:58
Some design and engineering professionals still have concerns about green roofing systems because many of the early US suppliers of green roofing relied on a very expensive and substantially built up system with deep profiles. These were also expensive and very heavy. But according to Clayton Rugh, Ph.D., manager and technical director, Xero Flor America, the modern approach is to use the minimally appropriate amount of material for each installation. “Our default approach is to avoid excessive soil depth because it’s unneeded. We know the soil depths for plants that are commonly used in green roofs, and we recommend that. The systems are among the lightest weight in the market and have many ancillary benefits, such as less material to buy and install, and lighter load bearing requirements, so many buildings can handle this load without expensive structural upgrades.” Most importantly from a sustainability perspective, horticulturally, the system is optimally designed for the dry climate conditions that are typical on a roof. It’s not overbuilt and won’t become attractive to aggressive and invasive weeds. The proper rooting depth and soil moisture profile resists supplemental maintenance that’s required to keep a roof performing as desired. So these are some of the concerns from an industry perspective. “Architects and builders that are only familiar with the deeper heavier systems don’t understand how a lighter system like ours can work,” adds Rugh. “Some companies recommend five to seven inches of soil, and we recommend one to two inches. In places like New York City where we have dozens of reference projects, and Seattle, Chicago, and Detroit, we have no problem with people understanding the technology. When they see a project that’s been on a building for 10 to 12 years and looks as good as it does, it sells them on using the strategy for their project.”
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