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Why EPDM?
Dave St. Hilaire, vice president of St. Hiliare Roofing Contractors, first suggested using the synthetic rubber terpolymer ethylene propylene diene methylene (EPDM) on Ledman’s project.


“We had considered other possibilities, but when he said, ‘Why don’t you put three inches of rubber foam down on this,’ it really appealed to me,” Ledman says. “So we looked at the cost and installation time and everything else, including local planning board approvals, and it was quickly obvious this was the best solution.”


While Ledman and his team ultimately decided on a EPDM roof, other options that were considered were PVC and TPO membranes, which are essentially single-ply, thermoplastic roofs that are hot-air welded together.


 


MAKING GARDEN ROOFS WORK
Lighter growing mediums and plants genetically engineered to thrive in inhospitable, rooftop environments are helping to increase the demand for garden roofs among residential homeowners.


In the mid-1970s, a Chicago company called American Hydrotech developed a waterproofing membrane—something National Marketing Manager Dennis Yanez describes as “hot rubberized asphalt” that had been incorporated into reflecting pools for years.


The biggest challenge for residential garden roofs has been weight. Residential structures can’t handle the same load as banks and office buildings.


American Hydrotech’s solution was a membrane made of recycled oil and used rubber, and a garden drain made of recycled polyethylene. They have designed the system to mimic the moisture retention, aeration and drainage of 2’ or more of topsoil in a 1” or 1.5” profile.


The medium, it should be noted, can’t sustain all types of plants. The main plant recommended is sedum, a drought and wind-tolerant alpine plant that has proven not to mind the harsh roof-top environment.


Many of the currently available garden roof products follow the same basic design.


 


ROOFTOP LANDSCAPING 101
St. Hilaire Roofing Contractors (see project in main bar) is installing a garden roof in Yarmouth, Maine: three attached homes that were a joint investment by three different couples.


David St. Hilaire says the initial phase of the project entails installing .075”-thick reinforced rubber on the expansive flat roof, and then installed redundant seaming and flashing to reduce the chance of leaks.


Once that part of the job is done, St. Hilaire will bring in a landscape company to install a Carlisle Roof Garden.


That garden is an engineered system, featuring drainage composite, a polypropylene root barrier, protection fabric, aluminium roof garden edging, aluminium drain boxes and a lightweight roof garden medium tailored to the varying climato-logical regions of the country.


St. Hilaire notes that a garden roof is a lot more work than a standard flat roof. “Before you even deal with the garden components, there’s the redundancy you have to build into the seams and flashing,” he says.


OTHER FACTORS ALSO COME INTO PLAY:


> EROSION. Misdirection of water runoff can cause stains or leaks in siding. You have to be mindful of the placement of drains, drainage media, and maintaining a proper distance between the growth media and the drainage media,” St. Hilaire says.


> STAYING POWER. “The other thing you have to think about is the proper construction to ensure that if it rains very hard, the whole thing doesn’t wash off the roof—which means creating little parapet walls, and then taking the extra step of making sure they drain properly too,” he says.


> LANDSCAPING. Manufacturers of garden roof systems typically provide exacting instructions on how the garden should be installed. St. Hilaire says no matter how experienced the builder is with such roofing systems, he should avoid the temptation to freestyle—for example, doing away with one of the layers of the growing medium for expedience’s sake. “Each layer serves an important function, and together ensure that the vegetation will survive,” he says. “In the worst case, the plants will die. Or they may grow too wildly, and the last thing anybody wants is to have to mow their roof.”


Garden roofs are more complex to install than a traditional flat roof, and also come with higher up front costs. However, when one factors in their green features, including storm water retention, increased energy efficiency, and reduced rooftop noise infiltration—their advantages often justify those early expenditures.


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