Because green roofs are relatively new and present different challenges than other types of roofs, managers can come across false or misleading information about the systems.
“It can be a myth or misconception that a green roof system can go on every single roofing type,” Stacy says. “You have to consider what the roofing membrane type is and the overall roof assembly components. Green roof assemblies have varying layers that may include, vapor retarder, insulation, cover board, roof membrane, root barrier, filter fabric, drainage layer, water retention layer, growth media and vegetation. There are differing requirements for the build-up of the green roof system depending upon the particular type of roofing membrane and project performance goals.
“The roofing membrane may also require enhanced detailing below a green roof system, such as additional strips over membrane seams in a single-ply system. You want to make sure the design of the green roof and the roofing assembly are working together so you have success.”
Managers also must be careful not to be misled by renderings of a green roof that include trees or other vegetation.
“One common misconception is that on day one, that's how the roof is going to perform if you have vegetation for those purposes,” Stacy says. “A lot of times, those calculations are done when the vegetation is fully mature, and renderings are going to be with a fully mature vegetation perspective.
“That's important to keep in mind: On day one, it's not going to look like the rendering. It's something for wind mitigation, and it might not perform until that particular element has reached maturation.”
The long-term success of a green roof often comes down to ensuring managers address the details of design, installation and maintenance, and that attention to detail should start early. Because green roofs differ from more traditional systems, managers face different considerations when selecting or inheriting a system. Their early involvement in design and installation of a green roof or the purchase of a building with a system can ensure long-term performance.
Facilities managers “are the first people we usually go to,” Totten says. “There's no one who knows the building better than the facilities manager. They know everything. Plug that expertise into the design phase when you can. We've had a couple of developers that have facilities managers come to the design review meetings. It makes a huge difference.”
Dan Hounsell is senior editor for the facilities market. He has more than 30 years of experience writing about facilities maintenance, engineering and management.
