Commercial Roofing Alternatives: Greener Choices

Commercial Roofing Alternatives: Greener Choices

Not all “cool roofs” are considered green; certain reflective alternatives pose significant environmental risks. Fortunately, today’s market offers some good choices that are both cool and green. By Henry S. Cole, Ph.D. and Sam A. Flewelling



Green building choices for roofs focus primarily on energy efficiency. Highly reflective roofs can dramatically lower air conditioning equipment operating costs during summer periods of peak power demand. The U.S. Environmental Protection Agency’s Energy Star certification for buildings includes performance standards for reflectivity.

However, not all “cool roofs” are considered green; certain reflective alternatives pose significant environmental risks. Fortunately, today’s market offers some good choices that are both cool and green.

Market Choices

Currently available types of commercial roofing can be categorized as follows:
  • Materials containing asphalt: includes “built-up roofs” and “modified bitumens”
  • Single-ply PVC (polyvinyl chloride) membranes: sheets of plastic fastened to the underlying roof substrate
  • PVC-free polymer and rubber membranes: includes TPO (thermoplastic polyolefin) plastic and EPDM (ethylene, polypylene, diene terpolymer) synthetic rubber
  • Metal roofing options
This article focuses on the first three options, which account for 90% of commercial roofs.

Asphalt

Built-up roofs (BURs) generally contain layers of fiberglass felts and asphalt with an upper granular layer for weather protection. Prior to the 1970’s, built-up asphalt roofs were ubiquitous. Despite declining share, BURs still accounts for 40% of the market.

According to a 2000 report by the U.S. Centers for Disease Control and Prevention, an estimated 50,000 workers are exposed to asphalt fumes in roofing operations (think hot applications and familiar pungent odor). According to the CDC report there is evidence that these workers experience irritation of eyes, nose and throat and acute lower respiratory tract symptoms. CDC states that there is sufficient evidence to conclude, “roofing asphalt fumes are a potential occupational carcinogen.”

While asphalt roofs can be colored white, they should not be labeled “green.”

Single-Ply Membranes: PVC or PVC-free?

Single-ply membranes, introduced in the early 1960’s, have increased in market share dramatically in recent decades. According to industry experts, they are lightweight, weather resistant, fast to install, and have lower labor costs than built-up roofs. The membranes can be made in a variety of colors. Highly reflective white is the best choice for warmer climates. However, darker colors may be better for cold climates. (Energy Star’s complete procurement guidelines are available online.)

Environmentally, the most important distinction is whether the product contains PVC or not. Although, all materials including plastics pose environmental impacts and risks, many environmental organizations (including U.S. PIRG, NRDC, the Healthy Building Network, Physicians for Social Responsibility, Environmental Defense) have called for alternatives and restrictions to PVC due to evidence that most stages of the product life cycle pose serious environmental health risks. These include:
  • Chlorine gas: more than half of the mass of PVC is chlorine. Acutely toxic chlorine gas is a leading cause of chemical accidents.
  • Carcinogens: According to EPA, nearly 800,000 lbs. vinyl chloride monomer (VCM) and over 500,000 lbs. ethylene dichloride (EDC) are emitted directly into air. The International Agency for Research on Cancer and the U.S. National Toxicology Program designate VCM as a known human carcinogen and EDC as a probable human carcinogen.
  • Phthalates: Plasticizers (e.g., phthalates used to make inherently rigid PVC flexible) and other additives are used to give products various attributes such as flexibility, weatherability, and color integrity. Phthalates have come under increased scrutiny due to their toxicity and tendency to accumulate in the environment and human tissue.
  • Dioxins: EPA’s “Inventory of Sources of Dioxin in the United States” cites numerous studies that indicate the combustion of PVC plastic (e.g., via incinerators and backyard burning) produces dioxin.
PVC-Free Alternatives

Major non-PVC single-ply membranes include TPO (thermoplastic polyolefin) and EPDM (a synthetic rubber). Both are based largely on polypropylene and polyethylene, relatively benign materials. Since TPO and EPDM are inherently flexible, they do not require plasticizers and other additives used in PVC-based materials.

Both TPO and EPDM have their strong points. For example, EPDM is considered to be the benchmark in resistance to weathering offered in black and reflective-white. White TPO is one of the best choices for energy efficiency where cooling needs are high.

Carlisle SynTec Incorporated in Carlisle, Penn., makes only PVC-free roofing membrane products including TPO and EPDM. According to Ron Head, marketing manager of the company’s thermoplastics division, “the very attributes which make our products environmentally preferable also lead to better performance and durability.” He explained that PVC-free materials don’t experience the loss of plasticizers or the dechlorination that occurs with PVC -- processes that may lead to accelerated deterioration and roof membrane failure.

Summary

There are a number of commercial roofing alternatives that are energy efficient. However, not all of them are made of environmentally preferable materials. The expanding market for membrane roofing has potential environmental benefits over traditional asphalt-based roofs. However, we advise owners, designers, and contractors aiming for green buildings to opt for PVC-free membranes such as EPDM and TPO.

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Henry S. Cole is founder and president of the Center for Environmentally Advanced Technologies. He is also president of Henry S. Cole & Associates, Inc., an environmental consulting firm.

Sam A. Flewelling is research director at Henry S. Cole & Associates, Inc.