Roofs and the Environment
Roofing materials often have a poor environmental reputation, but the industry is developing products and practices to help it become more green.Lush vegetation crowning the tops of buildings is what ...
Roofing materials often have a poor environmental reputation, but the industry is developing products and practices to help it become more green.
Lush vegetation crowning the tops of buildings is what many people envision when they hear the term “green roofing.” But rooftop gardens are just one facet of a growing movement toward sustainable roofing.
“To some, ‘green roofing’ means greenscaping the roof by planting vegetation, and to others green roofing is anything that moves the industry towards more environmentally benign activities,” says Peter Kalinger, technical director of the Canadian Roofing Contractors Association in Ottawa.
The broader definition is what concerns Kalinger and others in the industry. In 1995, experts from around the world formed the CIB/RILEM joint committee to investigate green roofing and advise contractors and designers on sustainable practices. (CIB is the International Council for Building Research Studies and Documentation. RILEM is the International Union of Testing and Research Laboratories for Materials and Structures.) The end result of the committee’s work is a list of best practices for low-slope membrane roofing1, the most common type of roofing for commercial and industrial buildings.
The committee used a definition of sustainable roofing that was first proposed in 1996 at a workshop held at the Oak Ridge National Laboratory in the U.S: “a roofing system that is designed, constructed, maintained, rehabilitated and demolished with an emphasis throughout its life cycle on using natural resources efficiently and preserving the global environment.”
By the committee’s own admission, the concepts embedded in the definition are difficult to comprehend, let alone implement. And the standards of durability designers look for in roofing products can conflict with some of the tenets of sustainability. But despite the complexities that arise when theory evolves into practice, the definition breaks down into three basic principals: preserve the environment; conserve energy; extend the life of the roof.
The National Research Council of Canada (NRC) Institute for Research in Construction, which has representation on the international committee, considers any long-lasting roof that incorporates mostly natural products and recyclable components as sustainable. The NRC’s “wish list,” says Bas Baskaran, P.Eng., leader of the roofing section, includes a service life of 25 years, 60% natural product and about 70% recyclable material.
The NRC is operating three programs designed to help the Canadian roofing industry become more environmentally benign. The first program is examining the costs and benefits of rooftop gardens. It will develop guidelines specific to Canada, where the climate was once considered too harsh for this type of roofing. The second initiative is developing a test protocol to determine the performance of different roofing membranes over a 10-year period, taking into account wind events. The third program is evaluating roofing membranes in the field to allow experts to predict degradation more accurately .
No simple answer
How do current roofing materials measure up to sustainability requirements? There are as many answers to this question as there are variables to consider. For example, the production of one material may meet the requirements for reducing ozone depletion, but contribute to CO2 emissions and global warming. Another material may be 100% recyclable, but without design modifications is impossible to separate from non-recyclable material when the roof is demolished. And not everyone is in agreement on how the different parameters should be weighed in determining overall ranking.
“It really depends on where you start the environmental analysis,” says Kalinger. “If you just look at the point at which the roof structure is built you may miss a lot of the hidden costs of the material.” For example, while metal roofs may look like the most sustainable choice because they last so long (up to 50 years for the copper roof that adorns Ottawa’s Parliament buildings) and because the material can be recycled, the pollutants emitted when the raw material is mined and smelted must be factored into the equation. Using a life cycle assessment, some of the traditional roofing materials, such as slate and wood shingles, move to the top of the pack.2
For several decades, the most popular material for commercial and industrial buildings has been built-up roofing (BUR) because it is relatively inexpensive, waterproof and fire resistant. BUR consists of multiple layers of bitumen and reinforcing sheets of roofing felt. A study of more than 25,000 roofs in the U.S. between 1975 and 1996 by the National Roofing Contractors Association calculated that the average service life for asphalt BUR roofs is about 13.6 years. Although design modifications have moved this life expectancy closer to 20 years, it is still short of the NRC’s 25-year goal. Asphalt is recyclable but, using current designs, the membrane is difficult to separate from the insulation. And, as with most roofing systems, there is little incentive to recycle.
“It [recycling the material] is not something a contractor would go out of his way to do because there’s no financial gain. It’s easier for him to throw [the material] away,” says Thomas Hutchinson, principal of Hutchinson Design group, a specialist in roof design based in Illinois. Indeed, an estimated 20 billion pounds of asphalt shingles are thrown into American landfills every year.
One of the best ways to encourage recycling is to modify roofing designs so that recyclable material can be separated from waste when the roof is demolished, according to joint research conducted by the Canadian Roofing Contractors Association and Public Works and Government Services Canada (PWGSC)3. Some of the proposed modifications include using reversible mechanical fasteners and connectors, applying higher-quality galvanization or other rustproofing measures, and installing a buffer between the insulation and the roofing membrane. The general principles identified by the study have been incorporated into the National Master Specifications for the Canadian construction industry.
Hutchinson is a proponent of EPDM (ethylene propylene diene monomer), a rubber product first introduced as a roofing material in the 1960s. EPDM has become one of the most popular roofing types because it is relatively clean and easy to install compared to built-up roofs. It also requires little maintenance. Hutchinson says that with proper design, ballasted EPDM roofs can fulfil most of the 21 tenets of sustainability developed by the CIM/RILEM joint committee. The material’s high marks for sustainability stem from its resistance to ultraviolet light and other weathering, and its potential for restoration.
“You can take membranes that are 20-30 years old, go up, clean them and put a patch on them and it’s as if they were brand new,” Hutchinson says.
The fastest-growing membrane types have been single-ply thermoplastic membranes. Some include PVC’s (polyvinyl chlorides) but another membrane type is the TPO (thermoplastic olefin). The roof of the Air Canada Centre in Toronto, for instance, features a 0.45-ml thick reinforced TPO membrane which is produced without plasticizers or chlorinated ingredients. These membranes combine the weathering and cold temperature resistance of EPDM systems with the heat-welded integrity of PVC systems.
Incentives can also encourage the industry to become greener. In California, the Energy Commission has just ended a program offering cash rebates for building owners who install “cool roofs.” These are roofs with highly reflective light roofing surfaces produced either by light-coloured coatings or single-ply roofing products. The operating principle is that dark materials absorb more heat than light materials, cutting down on energy use in the summer.
Some of the more radical approaches to greening the roofing industry in Canada include rooftop gardens or vegetative roofs (see p. 35) and photovoltaic systems to convert sunlight ener
gy into electricity.
An issue that remains to be addressed by the sustainability movement is cost. Some, though not all, of the greenest initiatives may simply be too expensive to implement. Another major hurdle is the often conflicting demands of durability and sustainability. The very qualities that designers look for in a roof — impermeability and resistance to weathering and fire — may preclude the use of materials that can be reused or recycled.
As a result of these challenges, the move toward sustainability needs more government leadership in order to gather lasting momentum. For example, the Montreal Protocol, which banned the production and import of hydrochlorofluorocarbons (HCFCs) by the end of 2002, changed the nature of roofing insulation dramatically by forcing the industry to develop CFC-free insulation products.
“In this case, the industry was moved towards a goal not because of technical performance issues, but by environmental regulations,” says Kalinger. Manufacturers now offer a range of CFC-free products, as well as other more environmentally benign insulation options, including water-blown semi-rigid polyurethane foams and insulation using recycled glass. There are also expanded polystyrenes that can be re-used and recycled.
Because there are no official standards or guidelines by which to judge sustainability, Kalinger cautions architects and designers to be wary of the “green” claims made by roofing product manufacturers. There are just too many variables.
In the end, after all the committee meeting minutes, parameter weightings and cost-benefit analyses have been compiled, the answer to the complexities of sustainable roofing may boil down to one simple factor: longer-lasting roofs.
“When you peel away the layers of the onion, there is a lot of what I call green marketing as opposed to green roofing,” he says. “What may seem green on the surface, may not really be green.” says Kalinger. “The best thing our industry can do with respect to enhancing the environment is to build better roofs so that they last longer.”
Virginia Heffernan is a freelance writer based in Toronto.
Hutchinson, T., 2001. “Designing environmentally responsive low-slope roof systems.” Journal of the Roof Consultants Institute. Pp. 13-20, Vol. IX (11) November 2001.
1 CIM/RILEM, 2001. Towards Sustainable Roofing. Report of the CIMW.83/RILEM 166-MRS Joint Committee on roofing materials and systems. July 2001.
2 for lifecycle assessments see BEES (Building for Environmental and Economic Sustainability). The software measures the environmental performance of building products using the life-cycle assessment approach specified in ISO 14000 standards. BEES was developed over the last eight years by the NIST (National Institute of Standards and Technology) Building and Fire Research Laboratory with support from the U.S. EPA.
3 Kyle, B., Kalinger, P., Bole C. and V. Catalli, 2000. Towards sustainable roofs via design for heightened maintainability and future disassembly. XIth International Waterproofing & Roofing Congress. Florence, Italy, 4-6 October 2000.