GSD Green Roof Initiative
Partner: Katrin Scholz-Barth, Environmental Engineer, Washington DC 2006-Present
Green roofs are on the rise in the US. 80% more green roofs were constructed in 2005 than in 2004. Although this statistic is very encouraging, green roofs still have a long way to go. Only 0.01% of all newly built and resurfaced roofs in the US are green. The ratio of green versus grey roofs is still miniscule compared to a country like Germany, where the rate is 7%, 700 times higher. This low overall US percentage is because the technology is a relatively recent import and still alien to the mainstream construction industry. Throughout Germany green roofs have been present for 20 to 30 years whereas in the US only for 5 to 7 years. The unfamiliarity of the technology makes green roofs more expensive than in Europe and builders tend to be reluctant to include them into their projects.
Under these circumstances, the GSD Green Roof Initiative was founded to study technologies that decrease overall installation costs. The intention is to promote widespread application of green roofs in the US by demonstrating that green roofs can be both ecological and economical.
The GSD Green Roof Initiative sought to study a low cost application on a real building and chose the roof of the Harvard Graduate School of Design as its subject. Since 2006 several installations have taken place on the roof of the school; collectively the installations have resulted in the greening of about 40 percent of the total roof area. Approximately 5,000 square feet are covered with Sedum sp. cuttings in separate plots within which a variety of soil mixes are being tested. The use of cuttings harvested from other projects contributed to the green roofs low cost, but perhaps more substantial savings were realized as a result of an in-depth pre-construction analysis of the hydrology, plant-soil dynamics, and the existing roof design, uses, and maintenance issues. Specifically, the current studio roof consists of gravel ballast on top of insulation and an EPDM rubber waterproof membrane. The existing roof membrane is made of a material that also performs as a root barrier. The simplicity of the pilot design thus emerged through the use of the existing gravel ballast as both the drainage course and the soil medium, thereby affecting cost savings in labor and materials.
If the GSD pilot program is successful, green roof cost estimates will decrease from approximately $4.00 - $10.00 per square foot to less than $2.00 per square foot. Developers and roofing contractors wont be able to afford to not go green and the cumulative benefits from wide scale coverage of green roofs will significantly improve the health and experience of cities.
In the meantime, the GSD Green Roof serves as a living experiment used for research and teaching in the school and nationwide. Many green roof experts, prospective builders and student groups from Harvard and various other universities have already visited the roof. Plant progress is closely monitored by the initiative. After one growing season the comparative success rates of different soil mixes can be already observed. A detailed technical report will be published following the third growing season (2009).