Cost/Benefit Questions

Can green roofs be combined with other green features?

Charlie says: Certainly! Green roofs can be designed in conjunction with other sustainable technologies, like solar panels. Plus, green roofs work very well in combination with other ‘low-impact’ development measures, such as infiltration beds, rain gardens, bio-retention systems, cisterns and rain barrels. In Germany, large developments often have zero runoff discharge. In these developments, rainfall is captured on the green roofs, returned to ground water through infiltration and re-used for irrigation, toilets and more. For more details, see Study of Extensive ‘Green Roofs’ in Berlin, by Manfred Köhler and Marco Schmidt.

Can recycled materials be used in constructing green roofs?

Charlie says: Short answer? Yes. However, when using recycled materials on a green roof there is a three-way interaction among quality, cost and performance. In general, we strive to use to the eco-friendliest materials possible, but, in some cases, the performance and cost compromises are just too high. So we “reduce” instead of “reuse.” Usually reducing preserves our natural resources better than recycling by removing the energy required to transport, reclaim and transform waste materials from the equation. Green roof systems that minimize the use of synthetic infrastructure altogether also reduce the consumption of both virgin and recycled synthetics – and the energy expenditures of their processing, as well. For example, the Roofmeadow® Type III system, utilizes only thin fabrics and natural growth and drainage media. The savings in materials and processing compares favorably with that of other systems using recycled, but higher mass components, such as plastic trays or water retention “egg cartons.”

How much does a green roof cost?

Charlie says: Cost per square foot depends on many factors: the size and slope of the roof, depth and complexity of the system, height and accessibility from the ground, labor costs and the need for specialized elements, like drains, railings, pavers, slope stabilization measures and more. To determine if a green roof will fit your budget, why not submit a Green Roof Worksheet, We’re always happy to help you determine which system best fits you.

What financial benefits do green roofs provide?

Charlie says: Thirty-five years of experience with green roofs in Germany have demonstrated that a roof assembly with a vegetative covering can be expected to outlast a comparable roof without a vegetated cover by a factor of at least two, often three. Although modern green roof systems have not yet been in place longer than about 35 years, many researches expect that these installations will last 50 years and longer before they require significant repair or replacement. For a building owner with a long-term investment in the roofing system, this benefit factor goes a long way toward paying back the initial investment.

Will a green roof save energy?

Charlie says: Yes, although not due to insulation or “r-factors.” A green roof acts as a thermal mass or heat sink, slowly absorbing and holding energy from sunlight and releasing it when the ambient air cools. In this way, it acts as a heat “storage battery” and reduces the heating and cooling demands within the building. Additionally, the latent heat transfer that occurs when the plants evapotranspire moisture also creates a cooling effect. Energy savings will be greatest in low buildings due to the high ratio of roof area to the total of exposed building skin. Our current research suggests that green roofs, even thin extensive assemblies, provide greater energy conservation in cold climates than in warm climates. To see how your site stacks up, we can facilitate a simplified building envelope analysis that can help set some reliable benchmarks for energy-related savings associated with a green roof design. Just drop us a line.

Are there incentives or grants available for green roofs?

Charlie says: At present, there are relatively few incentives offered for green roofs in the United States. However, Portland, Oregon and Philadelphia, Pennsylvania stand out as municipalities that promote green roofs through grants, zoning and stormwater regulations and tax breaks. If present trends continue, similar programs can be expected in other major metropolitan areas that are plagued by urban flooding, water pollution or urban heat island impacts.

Are there other incentives for using green roofs?

Charlie says: Beyond the warm, fuzzy feeling of environmental responsibility? Yes, a green roof can be an important element in LEED (Leadership in Energy & Environmental Design) green building certification — a standard that signifies the owner is an ecologically responsible community partner — while adding to the prestige of the building.