Green Roofs… Revisited

At my Greening workshop in Onondaga County last week I was confronted with a challenge to my answer that green roofs were not necessarily a great choice for buildings in the Northeast. When asked to expand on my statement I shared my feeling that while it is true they mitigate rainwater runoff, add insulation and combat the heat island effect in urban settings they are not cost-effective in terms of payback for libraries in NY and that adding them to existing buildings, particularly historic buildings, was not a great idea in terms of weight load and maintenance.

A speaker later in the day, who works for Onondaga County (OC), shared that the county was investing considerable funds  in green roofs. Since everything else the speaker reported on sounded fantastic and smart (really, it was, I’m not being sarcastic!) I started second guessing my assured answer that green roofs were not the way to go.

I did a bit of searching and learned that OC is under court order to reduce the amount of pollution flowing into Onondaga Lake with stormwater. The county is pursing a number of stormwater mitigation solutions, porous pavers, rainbarrels for residents… and testing out a green roof on a correctional facility. So to start off with I feel better that the case isn’t that they’ve invested millions of dollars into green roofs but that they are testing it out to see if it works for their situation.

This is a take-away folks: different green solutions work for different reasons. This county is faced with a specific problem – pollution caused by stomwater run-off – and is seeking solutions to rectify that. This does not mean that is the best solution for everyone but it may turn out that it can put a dent in a serious problem they are faced with.

Almost every green solution has a pro and con list to contend with. In New York City a study was done in 2007 to assess cool roof options:

So, as a general policy, DDC does not encourage the use of green roofs as a sustainability strategy on City
projects, and recommends more cost-effective, environmentally-beneficial strategies such as street trees, light-colored surfaces, and permeable paving–and building-related energy improvements. However, it is important to note that green roofs have numerous other benefits, primarily those in human terms. A green roof might be the right solution in a particular situation, and would be supported by DDC. Examples are:

  • As a public or staff amenity. Intensive green roofs can provide protected, usable outdoor space forlibraries, residential facilities and 24-hour agencies, such as Police and Fire. An extensive green roof might provide a welcome visual amenity for cultural institutions or a situation with a bleak view.
  • As a mission-related or educational tool. An example is the new building at the Queens Botanical Garden, where the green roof supports the Garden’s mission and is usable by visitors.

Although green roofs offer many benefits, they are not the environmental panacea sometimes put forth.
Design teams should review the project-specifi c goals, alternate methods of providing green open space
and controlling stormwater and craft an effective environmental approach.

  • From the report, “DDC Cool and Green Roofing Manual” Prepared for the NYC Department of Design & Construction Office of Sustainable Design by Gruzen Samton Architects LLP with Amis Inc., Flack + Kurtz Inc., Mathews Nielsen Landscape Architects P.C., and SHADE Consulting, LLC

So I guess the real answer here is what is your goal? What is the priority? And what is the right solution to address the goal? Simple payback formulas would show that it is not a cost effective option for energy efficiency but calculations may indicate it is a viable solution for stormwater management in a particular case.

As is the case with many green solutions this is not a clear cut answer but I find solace in my finding that it is a “right tool for the job” answer.

Greening Presentation for Onondaga County Public Library 5.7.10