Roofing Membranes

A membrane roof refers to a protective barrier that covers a roof assembly. Membrane roofs can be single-ply or multi-ply by laminating various materials. The most common roofing product is the build-up roofing system (known as BUR) which has been used in U.S. for over 100 years.³ Negative environmental and health impacts associated with BUR created a need for better roofing options. The alternatives and their considerations are outlined below.

PVC

PVC (vinyl) is a thermoplastic single-ply roofing solution. It’s made from a lower percentage of oil and petroleum than TPO or EPDM but can contain more than 25% orthophthalate plasticizers by weight and requires more hazardous chemicals to make than other types of plastic roofing.¹

• Considerations: Orthophthalates are endocrine-disrupting chemicals associated with numerous health effects. PVC production may have greater impacts on workers and fenceline communities relative to other plastics. PVC has end of life concerns, including its potential to form persistent, bioaccumulative toxicant dioxins when burned.¹

TPO

TPO (thermoplastic polyolefin) is a thermoplastic material, often produced as a single-ply membrane made of rubber and plastic polymers. Depending on maintenance, TPO has a lifespan of 30+ years. ²

• Considerations: TPO membranes typically contain less health and environmental hazards than other roofing products.¹ They are also made with polymers that are synthesized using fewer hazardous chemicals than PVC membranes. Its reflective and heat resistant properties categorize it as energy efficient.⁶ The rubber and polypropylene in TPO can be recycled, reducing waste. TPO is also free of halogens, making it safer for the environment.

EPDM
EPDM (Ethylene Propylene Diene Terpolymer) roofing refers to a single-ply membrane. This membrane is glazed in an adhesive and rolled into place.  EPDM’s lifespan is an estimated 30-50 years with proper maintenance. ²

• Considerations: Unlike bitumen-based membranes, EPDM does not have the effects of petroleum. EPDM membranes are made with a polymer that is synthesized using fewer hazardous chemicals than PVC membranes. EPDM does, however, contain process oils that are suspected carcinogens, and they have been found to leach zinc, which is toxic to aquatic life.¹ EPDM rubber can be recycled but its reuse should account for its toxicity. Since EPDM is thermoset, the seams cannot be heat-welded and require primers that can contain hazardous solvents like toluene, a developmental toxicant.

Green Roofs

Green roofing or “living roofs” incorporate planted vegetation over a waterproof membrane. These roofs capture water when it rains and release it through evaporation and plant use. This greatly reduces the rainwater entering the stormwater systems.

• Considerations: Green roofs are popular in urban landscapes, where they serve as habitats for wildlife and filter out pollutants and carbon dioxide from the air.⁷ Green roofs are more cost inducing upfront, but they are energy efficient. The natural insulation decreases heating and cooling loads in buildings.⁵