The green roof on a facility at Potash Hill, a Marlboro School of Music campus in Vermont, includes two turf areas with paving brick pathways. Albert Vecerka/ Esto Vegetative, or green, roofs have gained a hold in a growing number of commercial and institutional facilities because of their benefits related to stormwater management, energy efficiency and aesthetics. Green roofs are not without their challenges, though, for maintenance and engineering managers responsible for the roofs’ long-term performance.
By understanding the inspection, maintenance and overall management of green roofs, managers will be in a better position to help their facilities and organizations take full advantage of the systems’ benefits.
Vegetative roof systems consist of thin layers of living vegetation installed on top of conventional flat or sloped roofs. The vegetation can include grass, flowers, shrubs and trees planted over a waterproof roofing membrane.
Dan Cotter, director of facilities management with Potash Hill, a Marlboro School of Music campus in Vermont, participated in discussions related to the installation of a 1,123-square-foot vegetative roof on one of the campus’s buildings three years ago and knows the systems well. He says managers need to be vigilant about the installation of green roofs on their facilities.
“I was hesitant about putting it on,” he says. “I trusted the contractor to do the installation, but I was still pretty vigilant about that roof. We flooded it and let it sit for two days before we put any dirt on it to make sure it didn't leak.
“Depending on how the roof is actually constructed, look at every layer of installation before the next layer goes above it because you can't look at it later. Make sure the deck is flat with nothing that's going to create a puncture. Make sure the installation is put down properly and not with fasteners that are going to make issues for the rubber membranes."
The success of a green roof depends in large part on the ability of all of the involved parties to communicate in order to understand the challenges.
“The owner has to be willing to take on the additional maintenance involved, and in our case we felt very confident because we had this very good relationship between client, owner and contractor,” says Beth Kalin, who worked on the Potash Hill green roof design and installation as senior project architect with HGA, a design, architecture and engineering firm. “If there's any hesitation, that (relationship) really helps you trust each other and know that you're going to have a quality installation.”
Cotter says his facility’s vegetative roof has performed well since installation, even though he was hesitant initially, based in part on his experience managing the campus’s grounds.
“If we were putting anything with invasive roots or any trees, I'd be skeptical of doing that because they work their way through seams and any little crack,” he says. “They'll go through pipes. If you're planting grass, make sure you've got enough cover so that the grass roots don't make it down because then you'll lose the ability of the water to travel to the drains. Make sure the pavers are done in a way that the water can make it to the drains and heavy rains.”
Having accurate documentation on a green roof’s structure and components also is critical in ensuring technicians can perform inspections effectively.
“One of the big things that we see is when there's an issue on a roof, sometimes the locations of roof drains aren't always known,” says Amanda Stacy, assistant vice president for building enclosures with WSP. “From a maintenance perspective, it's always good to make sure that in the documentation, you have a roof plan of where all of those roof drains are located. On a green roof, you're going to have an inspection opening that ideally makes them a little bit more visible. Underneath paver systems, these roof drains can be more difficult to locate.”
Stacy also says when installing green roof components and pedestal paver systems directly over a roofing membrane, managers should consider installing courses to protect the roofing membrane.
“That might be a root barrier, for instance, underneath the green roof system,” she says. “It might also be a sacrificial layer of membrane underneath pedestals, wood sleepers or other components that can shift and cause abrasion or damage to the roof membrane over time. This is applicable with new green roof systems or in cases where you are installing a green roof system on to an existing roof.”
Beyond the design and installation phases of a green roof, proper inspection and repair practices will ensure the system’s long-term performance, but the process presents unique issues for managers.
“It becomes a daily or weekly maintenance item, unlike a normal roof that you don't touch it until you have an issue with it.” Cotter says. “We do have to mow it. We will have to do maintenance on the pavers because there are paving pathways on it. It basically makes it more of the maintenance of a lawn or a pathway than it does roof maintenance.
“For anybody putting a green roof on a facility, especially if they have flat roofs, the base of that roof is like any other roof. There's insulation, a membrane and roof drains. When you have those, you can have a leak coming through the ceiling at Point A, but the actual leak in the membrane can be 40 feet to the north by the time it makes it through the insulation onto the sheet pan to where it can find a way out of the roof. In that normal case, you can usually walk around the roof, see the air bubbles and find the leak. We wouldn't have that option.”
Paul Totten, vice president and national practice leader for building enclosures with WSP, a consulting engineering firm, advises managers to consider electronic field vector mapping (EFVM) technology to provide advanced roof inspection. With an EFVM system, an electric field is created by applying water on the membrane and using the water as a conductive medium. The system delivers a low-voltage electrical charge between the non-conductive waterproofing membrane and the conductive structural deck. A watertight membrane will isolate the potential difference. Membrane breaches will cause an electrical connection to occur.
“It will help identify what zone in which you may be having water infiltration below a green roof,” Totten says. “You've got all this overburden, so it's more difficult than with just a hardscape area, where we may be able to more easily pull off stuff to go look for it. Those are tricky to find.”
Green Roof Installation, Inspection and Maintenance
