This month's questions are answered by Angie Durhman, green roof program manager for Tecta America, spray foam consultant Mason Knowles, and Brad Burdic, manager of sales and marketing for Ecostream. If you have a question specific to green roofing, spray foam or solar roofing, please email RSI Editor-in-Chief Thomas Skernivitz at tskernivitz@questex.com.

Q: What makes a green roof sustainable?

Durhman

A: Let's face it — there is a lot of green washing going around. It is one thing to promote an environmental image, but it is another to follow through and walk the walk in terms of creating a sustainable technology, so this is an excellent and timely question.

Green roofs should be designed to last a long time with minimal inputs. Attention to the microclimate is important when working on the design and choosing products. Maintenance, albeit minimal, should be as critical as choosing the right contractor to do the installation. With this recipe for a green roof in place, you're off to a good start.

A healthy green roof is a living system that is changing and adapting. Minimal inputs to the system — supplemental water and other amendments — should be addressed during the maintenance visits. A green roof will continue to be sustainable if it receives these minimal inputs (which could actually come from nature). In terms of appearance, the field should be 80 percent to 90 percent covered with plants proven to survive that microclimate. There should never be ponding water on the surface of the system. A healthy green roof will also go through periods of dormancy throughout, so don't expect the same scene every time you visit the rooftop. Lastly, in determining the sustainability of a roof, evaluate the entire field — don't nitpick every individual plant. The living roof creates its own ecology. Keep in mind, some German green roofs are more than 100 years old. That's sustainable! — AD