2) Set Achievable Goals
Before starting a project, there are several questions to ask yourself.
“What are your objectives? What is your motivation? Is it aesthetics? Is it reducing energy demand or retaining stormwater on-site?” says Jordan Richie, director of education and accreditation with Green Roofs for Healthy Cities (GRHC), a nonprofit industry association. “After knowing this, manufacturers can work with you to find the system that best suits your building.”
The improvements a green roof offers will also factor into your cost-benefit analysis and help rationalize a sizable investment. Installed cost ranges from $12 per square foot to above $30, says Rugh.
At certain times of the year, green roofs cut energy use. During cooling season, they act as an insulator and decrease heat flow through the roof. “As the water in the system evaporates, it leaves the membrane cooler and your HVAC system works less,” explains Andy Creath, owner and founder of Green Roofs of Colorado, a green roof services firm.
Likewise, the same insulating effect of lessening heat loss reduces heating needs during winter. A Canadian study modeled savings from a 32,000-square-foot green roof on a one-story building in Toronto and found savings of 6% cooling and 10% heating usage, or about 21,000 kWh total, according to the EPA.
In certain areas of the country, installing a green roof can also allot you extra building or parking space because it offsets your area of impermeable pavement, says Griswold.
The main economic benefit of a green roof is increased roof life expectancy due to the protection it provides to the membrane, says Griswold. Membrane life can be extended two to three times, says MacDonagh, adding that the GRHC’s green roof calculator is an important resource to use for your particular situation.
“A green roof costs about the same as reroofing, so the ideal scenario is to couple a green roof project with reroofing,” Rugh suggests. (See case study #3 on page 34.) “Then about 15 years down the line, you basically get a free roof. It’s a two-for-one special.”