The roofing industry has played an active role in developing interest in sustainable building design and construction. Single Ply Roofing Industry (SPRI) members support this initiative and have adopted a proactive approach to sustainable roof systems.
Although the industry has for nearly a decade embraced certain green design features, such as energy saving reflective surfaces and HCFC-free manufacturing techniques, the current level of interest has grown largely because of the formation of the U.S. Green Building Council (USGBC) and its popular Leadership in Energy and Environmental Design (LEED) Green Building Rating System. Municipalities, trade groups, and nongovernmental organizations (NGOs) are adopting similar green design guidelines. The USGBC attempts to focus on the whole building and its systems—energy consumption, water usage, occupant comfort and health, and building and component reuse.
Similarly, SPRI members define a sustainable roof system as one that provides a long service life, saves energy, uses natural resources efficiently, and preserves the quality of the global environment. Although energy efficiency and the attendant reduction in fossil fuel consumption are perhaps the most recognized and easily measured traits of sustainable buildings, life cycle performance is an equally important characteristic of a sustainable roof system.
Sustainable Roof Systems
A roof system consists of three and sometimes four basic components: structural roof deck, vapor/air retarder, thermal insulation, and waterproofing membrane. A sustainable roof system also consists of these basic components but additionally includes the environmental aspects of the design that affect the choice of components and their manufacturing processes, the installation procedures, evaluation of roof life expectancy factors, in-service performance and maintenance of the roof, and the reuse, recycle, or disposal of the components. Since roofing materials, according to Oak Ridge National Laboratories (ORNL), represent a significant percentage of the total solid waste discarded in landfills, reduced roof replacement, material recycling, and extended life cycles contribute to sustainable building goals.
In addition, research indicates a direct correlation between premature roof failures and “lowest first cost” design criteria, often the driving force behind the roof system selected for installation. Unfortunately, sustainable roof design strategies often run head-on into these “lowest first cost” design criteria. Many roofing professionals can show that the adoption of sustainable principles will result in longer lasting roof systems and, in turn, yield equal or greater savings than those promised by “lowest first cost” construction.
SPRI members have consistently focused on improving roof system performance characteristics, including durability, moisture control, and wind resistance. In addition to these sustainable attributes, some roof systems are reported to help reduce heat island effects and promote energy efficiency. However, just as there are multiple shades of the color green, SPRI members emphasize that the sustainability benefits of roof systems are made up of a variety of factors, including building and roof design, deck type, thermal insulation requirements, membrane type, color, thickness, composition, and method of installation.
The three primary membrane types manufactured by SPRI members include Modified Bitumen, Thermoplastic, and Thermoset. Each type offers distinct sustainability characteristics. For example, modified bitumen membranes (SBS and APP) offer good resistance to aging, UV resistance, and flexibility in low temperatures. Current cold applied systems and emerging self-adhered (“peel and stick”) technologies reduce exposure to asphaltic fumes and job site VOC emissions. Similarly, Thermoplastic (TP) roofing membranes, which include PVC (Polyvinyl Chloride), TPO (Thermoplastic Polyolefin), and KEE (ketone ethylene ester), among others, are seamed on the roof using a heat welding or seam tape technology that is environmentally safe and effective. Although thermoplastic roof membranes can be manufactured in a variety of colors, they are usually white, providing high reflectivity, often cited for energy and heat island reduction. Thermosets, most notably EPDM, also are known for good life cycle costs, are available in a white membrane option, and have low environmental impact during installation.
Regardless of the membrane type, SPRI members emphasize the importance of thermal insulation to reduce fossil fuel consumption and operating costs of the building. In addition to providing thermal resistance (R-value) to maximize energy efficiency, tapered roof insulation can also play an important role in the proper drainage of the roof, often cited as a key to roof system durability. For these reasons, most membrane manufacturers include rigid board insulation as part of their system and warranty. Other sustainable characteristics of roof insulation may include thermal stability, protection of the ozone layer, and reduction of global warming. Common roof insulation types include polyiso, expanded polystyrene, extruded polystyrene, perlite, and lightweight insulating concrete.
Sustainable Roof Design Choices
According to SPRI members, all single ply roof systems have sustainable attributes. Choosing among them is the design professional’s responsibility when specifying a sheet membrane roof system. These green attributes will assume a higher priority in a project seeking LEED certification or similar green design. Sheet membrane roof systems in general provide long service life, thereby resulting in an appealing life cycle cost, the leading factor in sustainability. Operating costs related to energy use are most affected by decisions regarding insulation and are usually driven by cost-benefit analysis and code compliance.
After these basic choices have been made, the designer must consider recycled content of materials, location of manufacture to construction site, recycling potential, as well as membrane reflectance and emittance. These latter features help to define a “Cool Roof” and may be required as part of a certification process or legislative requirement. For example, some products offered by SPRI members qualify for the EPA’s Energy Star label, which certifies that a product meets certain energy-efficiency guidelines and indicates the EPA’s belief that certified products help reduce the air conditioning needed in buildings and may reduce peak cooling demand by 10 to 15 percent. Based on these assumptions, white reflective roof systems with added insulation provide significant cooling cost reductions.
SPRI members caution that it might be easy to assume that only light-colored materials reflect sunlight and are therefore cooler than dark colored materials. However, some darker roofing materials’ surfacing and chemistry provide high reflectance performance. In addition, research is currently being conducted by SPRI and Oak Ridge National Laboratory (ORNL) to determine the reflectivity of ballast on single ply membranes.
Based on this work so far, ballasted single ply systems may also assist in reducing membrane temperatures and hold promise as an emerging cool roof system. Similarly, garden roofs are also considered cool roofs although their reflectivity is well below the required minimum to meet certain specifications. The combination of soil and plant life on these roofs helps to reduce heat island effect, clean pollutants from urban air, reduce energy use, and reduce storm water runoff. “You can get a cool roof in almost any material you might be considering,” says Andre Desjarlais, group leader in the Building Envelope Research Program, Oa
k Ridge National Laboratory. SPRI members also caution that potential savings associated with reflective roofs depend on variables such as climate, materials, insulation, and regional energy prices.
The integration of “Green” into project specifications requires some extra effort and begins by defining green project design criteria. Green specifications derived from this effort can provide value to stakeholders by providing written instructions and documentation requirements for green designs that address healthier work environments, energy and resource conservation, recycling programs, and overall environmental stewardship. Equally important, the specifications should also address the life cycle of the building from concept to deconstruction.
Determining the sustainability of building products or assemblies is a complex process, and no less so is green specification development. Bringing some order to this process requires greater understanding and additional education of the building team. Through organizations like SPRI, the building team can gain useful information that leads toward some clarity in the green design process.
SPRI members believe that becoming better environmental stewards requires constant, unwavering, and unending attention. The challenge facing the building team, however, remains overcoming “lowest first cost” design and construction criteria and replacing that approach with sustainable design criteria based on life cycle performance. SPRI and its individual member companies remain committed in their support of that goal and believe that environmental stewardship is everyone’s responsibility.