So you want to roof green?

Manufacturers provide several options for waterproofing green roofs

  • The Seaport Hotel, Boston, features a green roof by Carlisle SynTec Inc., Carlisle, Pa.Photo courtesy of Carlisle SynTec.
  • Sarnafil Inc., Canton, Mass., provided the waterproofing materials for the green roof on Chicago's City Hall. Photo courtesy of Sarnafil.
  • The tallest apartment building in Missouri, the 909 Walnut Fidelity Tower Building, features a green roof by Soprema Inc., Wadsworth, Ohio.Photo courtesy of Soprema.
  • W.P. Hickman Systems Inc., Solon, Ohio, offers many options for its green roofs, one of which is pictured here.Photo courtesy of W.P. Hickman Systems.

The roofing industry has been on the cusp of an environmental revolution during the past several years. In response, manufacturers have been introducing highly reflective and emissive membranes and coatings, reflective granules for shingles and, of course, "green" roofs.

But green roofs entail a unique approach to waterproofing, as well as added weight on a building's structure. Several waterproofing options are available in the marketplace—it's finding the right one for a given project that can prove challenging.

Professional Roofing interviewed representatives of several manufacturers that offer waterproofing materials for green roofs to explore their approaches to waterproofing. We spoke with Mike DuCharme, director of product marketing for Carlisle SynTec Inc., Carlisle, Pa.; Carl Kuhn, architectural representative of Soprema Inc., Wadsworth, Ohio; Tony Nista, director of marketing for W.P. Hickman Systems Inc., Solon, Ohio; and Gary Whittemore, product manager of waterproofing for Sarnafil Inc., Canton, Mass.

It should be noted the manufacturers interviewed are not the only ones who manufacture green roof system materials—there are many other materials and manufacturers.

Carlisle SynTec

Carlisle SynTec's initial foray into waterproofing for green roof systems began during the 1960s when the company's EPDM roof membranes were used to waterproof planters, plazas and paver areas.

But the company's oldest green roof in the traditional sense is an intensive system that is 1-foot (0.3-m) deep installed on the First United Church of Christ in Carlisle. Carlisle SynTec's waterproofing materials usually specified are EPDM and TPO though DuCharme says the company's single-ply hot-mopped technology also is an alternative.

"EPDM and TPO membranes offer resistance to moisture absorption and soil acids from bacteria," DuCharme explains. "Typically, the membranes that are used are designed to provide added durability and puncture resistance. As such, the membranes specified are 60 mils [0.06 of an inch (1.5 mm)] to 90 mils [0.09 of an inch (2.3 mm)] thick. Such membranes withstand the rigors of phased construction where a roof typically is installed before installation of a rooftop garden. The membranes also provide outstanding flexibility so the roof systems can handle the loads. EPDM and TPO membranes also are excellent at dealing with dead-level conditions and ponded water so they are able to deal with the conditions typical on green roofs."

Carlisle SynTec manufactures all of its membranes, as well as drainage composites. As a result of manufacturing its own products, the company has been able to improve upon its products by recognizing potential drawbacks.

DuCharme says the development of new drainage composites has been instrumental in helping the company facilitate drainage while reducing the weight of the overall assembly. He says the drainage composites provide a level of efficiency equal to 4 inches (102 mm) of gravel.

"The key improvements have been in the development of more user-friendly treatments to address the installation of green roofs," DuCharme says. "Tray systems permit roofing contractors to easily install green roofs without depending on landscape contractors. The sod products also give contractors an option to accomplish the installation of a green roof without having to handle seeding and plantings."

However, as DuCharme points out, all green roofs have limitations.

"Green roofs are limited because a structure must be able to handle the weight," he says. "Green roofs can vary in weight from a little more than 10 pounds [4.5 kg] to much more than 20 pounds [9 kg]. When a roof incorporates pavers, water features, trees, etc., the weight considerations are even greater. It's imperative a structural engineer be consulted for the design of green roofs."

He also recommends building owners hire roof consultants to help ensure green roofs are installed correctly.


Sarnafil, a company with its roots in Europe, has been providing waterproofing materials for green roofs in the U.S. for more than 25 years and more than 35 years in Europe. The primary product the company produces for such applications is a fiberglass-reinforced PVC sheet with a standard thickness of 80 mils (0.08 of an inch [2 mm]) though the sheet also is available in thicknesses of 60 mils (0.06 of an inch [1.5 mm]) and 96 mils (0.96 of an inch [2.4 mm]).

Whittemore says PVC provides some unique advantages for use on green roofs.

"PVC sheet membranes are able to perform in ponded water conditions and be subjected to dry/wet cycling, plant fertilizers, chemicals, fungi and bacterial organisms," Whittemore explains.

Whittemore also says Sarnafil's PVC sheet, which the company manufactures, acts as a root barrier and heat-welding the seams provides resistance to moisture infiltration. The sheet is bright orange to increase visibility to landscape providers should a roof area ever need to be uncovered.

In addition, Sarnafil offers what it calls a monitoring service, which means a Sarnafil "inspector" is on-site to ensure the materials are installed properly and conduct a final inspection to confirm there are no leaks before placing an overburden of material on the roof system.


Soprema's first U.S. green roof project was about 14 years ago on the Wearhauser building in Seattle. Since then, the company has provided waterproofing materials for the green roofs on the St. Louis Zoo and tallest apartment building in Kansas City, Mo., among other notable projects.

The company uses hot-fluid-applied membranes, SBS-modified bitumen torched membranes and self-adhered membranes to waterproof green roofs and manufactures about 95 percent of its products.

Kuhn says an advantage of the company's waterproofing system is the use of a reinforced cap-ply sheet that stands up to the burden of a green roof. Kuhn says the material has good abrasion resistance. In addition, the company recently introduced a capillary mat that can retain twice the rainwater of conventional mats.

W.P. Hickman Systems

For the past 21 years, W.P. Hickman Systems has been designing and manufacturing roofing and waterproofing materials. But it's only been during the past six years or so that the materials have been used actively for green roofs. W.P. Hickman Systems offers a range of materials that can be used for green roofs, including built-up and modified bitumen.

"W.P. Hickman Systems constantly is evolving to meet the ever-changing design concerns," Nista says. "More dynamic structures and sensitivity to environmental concerns compel us to be creative and innovative. Therefore, our product line includes a mixture of the oldest, best-recognized waterproofing materials known to man, such as coal-tar-based products, and some of the newest technology available, such as hybrid polyurea coatings."

Nista believes that because W.P. Hickman Systems offers many options, it is easier for design professionals, contractors and building owners to design a roof system based on special needs.

Regardless of the system chosen, consideration always must be given to the issue at hand—placing a large amount of soil and plant life (and water) on the roof of a structure.

"Materials must be able to withstand a different set of elements, including near-constant submersion in a dark, moist environment. Other elements to address include root penetration and mold and fungus, for example," Nista says. "Obviously, the right blend of waterproofing and elastomeric modifiers, combined with premium reinforcements, is necessary to perform under such conditions."

Making the leap

Installing green roofs definitely has benefits, but you need to ensure the materials are appropriate for the conditions, the system you choose stands up to the load placed on the building and the building owner is aware of the potential risks a green roof system presents.

Ambika Puniani Bailey is editor of Professional Roofing magazine.


The term "green roof" has proved elusive to define. Generally, green roofs are considered protected membrane roof systems that have landscaping material on top to protect the membrane from climatic extremes, ultraviolet exposure and mechanical damage.

There also are different types of green roofs. An extensive green roof is lightweight with soil depths as shallow as 3 inches (76 mm) and supports only hardy plants. Such systems require little ongoing maintenance and no supplemental irrigation.

An intensive green roof can support a wider variety of plants, shrubs and small trees. These systems require deeper soil depths, as well as regular maintenance and irrigation. Soil depths for intensive green roofs can be more than 8 inches (203 mm), which means consideration must be given to the load applied to a structure.



Be the first to comment. Please log in to leave a comment.