Here is some general guidance to use when choosing roofing membrane materials for flat or low-slope roofs:
This Hazard Spectrum focuses on the most common systems employed in commercial or residential low-slope roofing. In addition to creating a water-tight seal that protects the interior of the building, different types of roofing may be used to reduce a building’s contribution to climate change. Roofs – especially flat ones that can span hundreds of thousands of square feet – can contribute to climate change in two ways. Sunlight absorbed by a roof turns into heat, which can pass through to the interior environment, adding to air conditioning loads. Roofs can also re-emit heat, adding to the urban heat island effect.
Choices can be made in roofing membrane procurement to minimize both effects. This goal is embodied in the Solar Reflectance Index (SRI), which combines reflectance (its ability to reflect sunlight and heat) and emissivity (its ability to release absorbed heat). Depending on the climate where the building is located, different roofing materials may be recommended. For instance, in Southern climates, the ability of white membranes to reflect solar heating can reduce the amount of energy required to cool a building. In northern climates where heating days exceed cooling days, a darker membrane, such as a standard EPDM (Ethylene Propylene Diene Monomer) membrane, may reduce the energy required to heat a building.
While these considerations are important, it is also essential to understand the human and environmental health impacts of the chemicals in different types of roofing membranes and their accessory products. Roofing materials can release chemicals into the environment when exposed to the elements. Ultraviolet (UV) radiation, rainfall, and wind attack the roofing membrane and impact the product’s performance and longevity. In humid climates, moisture feeds the growth of algal species, which can impair reflectance. For this reason, some types of membranes require stabilizers and antimicrobial pesticides to combat the elements. While the extent to which roofing membranes contribute to environmental pollution is not fully understood, trace metals, plasticizers, flame retardants, solvents, stabilizers, antioxidants, and other types of chemicals are known to leach out of roofing membranes and can contaminate surface water.
The chemicals used in roofing membranes can also impact human health. Installers can be exposed to harmful chemicals, in particular from products that are wet-applied or heated. They can also be exposed to hazards from adhesives, primers, and coatings used during installation. Building occupants may also be exposed if the building is occupied while roofing work is being done and chemicals enter through the air intake for the ventilation system. In addition, communities living near facilities that manufacture the substances that go into these roofing materials can be impacted by chemical releases into their surroundings.
Here is some general guidance to use when choosing roofing membrane materials:
TPO membranes typically contain less human health or environmental hazards than other roofing products. They are also made with polymers that are synthesized using fewer hazardous chemicals than PVC membranes.
While TPO membranes are associated with the fewest health and environmental hazards, look for membranes that have a proven track record of performing well and have passed accelerated weather tests.
Like TPO membranes, EPDM membranes are made with a type of polymer that is synthesized using fewer hazardous chemicals than PVC membranes. EPDM membranes, however, contain process oils that are suspected carcinogens, and they have been found to leach zinc, which is toxic to aquatic life. In the past, some EPDM membranes used halogenated flame retardants. As a class of chemicals, halogenated flame retardants can be persistent, bioaccumulative, and/or toxic and should be avoided. While current data indicates that non-halogenated flame retardants are used in some EPDM membranes, flame retardants are not always disclosed. If selecting a system utilizing EPDM membranes, verify with the manufacturer that only non-halogenated flame retardants are used. Since EPDM is thermoset, the seams cannot be heat-welded and require primers that can contain hazardous solvents like toluene, a developmental toxicant.
Standard polyvinyl chloride (PVC) membranes contain more than 25% orthophthalate plasticizers by weight. Orthophthalates are a concern because they are endocrine-disrupting chemicals that can mimic hormones and consequently are associated with numerous health effects. They are liquid plasticizers that are known to migrate out of the roofing membrane over time. Some PVC roofing membranes use KEE (Ketone Ethylene Ester), a plasticizer that is better retained by the membrane than traditional liquid plasticizers, allowing it to remain flexible over longer periods of time. There is very little disclosure in chemical content available for KEE membranes, but these membranes still contain some liquid plasticizer. PVC roofing membranes also contain antimicrobial pesticides, with some products likely using arsenic-based compounds. Arsenic is considered a persistent and bioaccumulative toxicant.
Another important consideration is that more hazardous chemicals are required to make PVC, and more hazardous chemicals are created when it is disposed of than for other types of plastic roofing membranes. Consequently, PVC production may have greater impacts on workers and fenceline communities.
Modified bitumen roofing is a form of multi-ply roofing made from sheets of asphalt containing either styrene butadiene styrene rubber (SBS) or atactic polypropylene (APP). The addition of these substances reduces the number of layers required in the membrane compared to asphalt alone. These membranes can either be torch-applied or applied with hot- or cold-applied adhesives, with each method posing hazard concerns for workers. Modified bitumen roofing contains a large amount of asphalt. Particular chemicals of concern in asphalt are polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens. PAHs and other chemical emissions are expected to increase in torch-applied installations where membranes are heated. Occupational exposure to bitumen and bitumen fumes during roofing has been identified to be ‘probably carcinogenic to humans’ by the International Agency for Research on Cancer (IARC). In addition, asphalt production results in releases of PAHs into the air, potentially affecting manufacturing workers and people living in nearby communities.
Cold fluid-applied polymethyl methacrylate (PMMA) waterproofing systems are comprised of several products that together create a water-resistant barrier. The membrane is formed by reacting chemicals on-site in the presence of a catalyst. Much of the product is made up of respiratory sensitizers, including methyl methacrylate and other acrylates. The catalysts can contain phthalate plasticizers that are known developmental and reproductive toxicants and endocrine disruptors. The primers can also contain carcinogenic solvents. Furthermore, while PMMA requires fewer hazardous chemicals to produce than some other types of plastic, it requires the use of more hazardous chemicals than polypropylene and polyethylene, so it may have greater impacts on workers and fenceline communities.
Built-up roofing is composed of alternating layers of asphalt (also referred to as bitumen) and reinforcing felts. The asphalt can be either hot- or cold-applied. Occupational exposure to bitumen and bitumen fumes during roofing has been identified to be ‘probably carcinogenic to humans’ by the International Agency for Research on Cancer (IARC). In addition, asphalt production results in releases of carcinogenic polycyclic aromatic hydrocarbons (PAHs) into the air, potentially affecting manufacturing workers and people living in nearby communities.
BUR is generally expected to have a longer service life than other types of membrane roofing. However, it can require significantly more material than other types of products. For instance, BUR can use roughly twice the amount of asphalt as modified bituminous roofing membranes. Thus, the longer service life is not expected to offset its greater human and environmental health impacts.
Spray polyurethane foam (SPF) roofing is similar to closed-cell SPF insulation used in building interiors. It is sold as a two-part liquid that is then combined and applied on-site. Part A is a mixture of isocyanates, and Part B is a mixture of polyols and various additives. The reaction produces polyurethane and releases small amounts of isocyanates and other chemicals into the surrounding area, which can expose installers and others in the vicinity to these hazardous ingredients.
Isocyanates are asthmagens and have been identified as a leading cause of work-related asthma by organizations like the US Occupational Safety and Health Administration (OSHA). Part B of the foam mixture includes a halogenated flame retardant. Halogenated flame retardants are considered a very high concern to avoid because they can be persistent and toxic. Closed cell spray foam also commonly uses a blowing agent that is a highly potent contributor to global warming. While some formulations use blowing agents with low global warming potential, chemicals with high global warming potential can still be used to produce them.
SPF roofing requires a coating to be applied within 24 hours of installation. Various types of coatings are available, and each can contribute additional hazards.
Unless otherwise noted, product content and health hazard information is based on research done by Healthy Building Network for Common Product profiles, reports, and blogs. Links to the appropriate resources are provided.
 US EPA, OAR. “Heat Island Effect.” Collections and Lists, February 28, 2014. https://www.epa.gov/heatislands.
 U.S. Department of Energy. “Guidelines for Selecting Cool Roofs,” July 2010. https://www1.eere.energy.gov/buildings/publications/pdfs/corporate/coolroofguide.pdf.
 De Buyck, Pieter-Jan, Stijn W. H. Van Hulle, Ann Dumoulin, and Diederik P. L. Rousseau. “Roof Runoff Contamination: A Review on Pollutant Nature, Material Leaching and Deposition.” Reviews in Environmental Science and Bio/Technology 20, no. 2 (June 1, 2021): 549–606. https://doi.org/10.1007/s11157-021-09567-z; De Buyck, Pieter-Jan, Olha Matviichuk, Ann Dumoulin, Diederik P. L. Rousseau, and Stijn W. H. Van Hulle. “Roof Runoff Contamination: Establishing Material-Pollutant Relationships and Material Benchmarking Based on Laboratory Leaching Tests.” Chemosphere 283 (November 1, 2021): 131112. https://doi.org/10.1016/j.chemosphere.2021.131112; Bandow, Nicole, Stefan Gartiser, Outi Ilvonen, and Ute Schoknecht. “Evaluation of the Impact of Construction Products on the Environment by Leaching of Possibly Hazardous Substances.” Environmental Sciences Europe 30, no. 1 (May 15, 2018): 14. https://doi.org/10.1186/s12302-018-0144-2; Bandow, Nicole, Frederike Jürgens, and Ute Schoknecht. “Beregnete Bauteile Und Bauprodukte: Entwicklung von Vergabekriterien Für Den Blauen Engel Mit Hilfe von Auslaugtests.” Berlin, 2018. https://www.umweltbundesamt.de/publikationen/beregnete-bauteile-bauprodukte-entwicklung-von.
 Blum Arlene, Balan Simona A., Scheringer Martin, Trier Xenia, Goldenman Gretta, Cousins Ian T., Diamond Miriam, et al. “The Madrid Statement on Poly- and Perfluoroalkyl Substances (PFASs).” Environmental Health Perspectives 123, no. 5 (May 1, 2015): A107–11. https://doi.org/10.1289/ehp.1509934; Green Science Policy Institute. “PFAS Central.” Accessed December 15, 2021. https://pfascentral.org/
 Based on personal communication with BuildingGreen. January 24, 2022; BuildingGreen. “Membrane Roofing.” BuildingGreen. Accessed January 27, 2022. https://www.buildinggreen.com/product-guide/membrane-roofing
 De Buyck, Pieter-Jan, Olha Matviichuk, Ann Dumoulin, Diederik P. L. Rousseau, and Stijn W. H. Van Hulle. “Roof Runoff Contamination: Establishing Material-Pollutant Relationships and Material Benchmarking Based on Laboratory Leaching Tests.” Chemosphere 283 (November 1, 2021): 131112. https://doi.org/10.1016/j.chemosphere.2021.131112.
 DiGangi, Joseph, Arlene Blum, Åke Bergman, Cynthia A. de Wit, Donald Lucas, David Mortimer, Arnold Schecter, Martin Scheringer, Susan D. Shaw, and Thomas F. Webster. “San Antonio Statement on Brominated and Chlorinated Flame Retardants.” Environmental Health Perspectives 118, no. 12 (December 2010): A516–18. https://doi.org/10.1289/ehp.1003089.
 Gore, A. C., V. A. Chappell, S. E. Fenton, J. A. Flaws, A. Nadal, G. S. Prins, J. Toppari, and R. T. Zoeller. “EDC-2: The Endocrine Society’s Second Scientific Statement on Endocrine-Disrupting Chemicals.” Endocrine Reviews 36, no. 6 (December 2015): E1–150. https://doi.org/10.1210/er.2015-1010; Engel, Stephanie M., Heather B. Patisaul, Charlotte Brody, Russ Hauser, Ami R. Zota, Deborah H. Bennet, Maureen Swanson, and Robin M. Whyatt. “Neurotoxicity of Ortho-Phthalates: Recommendations for Critical Policy Reforms to Protect Brain Development in Children.” American Journal of Public Health, February 18, 2021, e1–9. https://doi.org/10.2105/AJPH.2020.306014; Bennett Deborah, Bellinger David C., Birnbaum Linda S., Bradman Asa, Chen Aimin, Cory-Slechta Deborah A., Engel Stephanie M., et al. “Project TENDR: Targeting Environmental Neuro-Developmental Risks The TENDR Consensus Statement.” Environmental Health Perspectives 124, no. 7 (July 1, 2016): A118–22. https://doi.org/10.1289/EHP358.
 GAF.com. “Single-Ply Roof Membrane Types and The Features of Each.” Accessed January 25, 2022. https://www.gaf.com/en-us/blog/single-ply-roof-membrane-types-what-are-they-and-how-do-they-differ-281474979982397.
 Mehta, Naresh R., Jeffrey Charles Flath, and David Allen Pettey. Roofing membranes. United States US8669196B2, filed May 23, 2008, and issued March 11, 2014. https://patents.google.com/patent/US8669196B2/en?oq=WO2009143432; Winters, Nancy, Kyle Granuke, and Melissa McCall. “Roofing Materials Assessment: Investigation of Five Metals in Runoff from Roofing Materials.” Water Environment Research 87, no. 9 (2015): 835–44. https://doi.org/10.2175/106143015X14362865226437.
 Ann Blake and Mark Rossi. “Plastics Scorecard.” Clean Production Action, July 1, 2014. https://www.cleanproduction.org/resources/entry/plastics-scorecard-resource.
 International Agency for Research on Cancer (IARC). “Occupational Exposures to Bitumens and Their Emissions,” 2011. https://www.iarc.who.int/wp-content/uploads/2018/07/IARC_Bitumen_Eng-1.pdf; International Agency for Research on Cancer (IARC). Bitumens and Bitumen Emissions, and Some N- and S-Heterocyclic Polycyclic Aromatic Hydrocarbons. Vol. 103. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. https://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Bitumens-And-Bitumen-Emissions-And-Some-Em-N-Em---And-Em-S-Em--Heterocyclic-Polycyclic-Aromatic-Hydrocarbons-2013; National Institute for Occupational Safety and Health (NIOSH). “Hazard Review: Health Effects of Occupational Exposure to Asphalt.,” December 2000. doi.org/10.26616/NIOSHPUB2001110;
 Based on U.S. EPA Toxics Release Inventory Data for releases of polycyclic aromatic compounds from asphalt plants in 2020.
 International Agency for Research on Cancer (IARC). “Occupational Exposures to Bitumens and Their Emissions,” 2011. https://www.iarc.who.int/wp-content/uploads/2018/07/IARC_Bitumen_Eng-1.pdf; International Agency for Research on Cancer (IARC). Bitumens and Bitumen Emissions, and Some N- and S-Heterocyclic Polycyclic Aromatic Hydrocarbons. Vol. 103. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Accessed January 25, 2022. https://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Bitumens-And-Bitumen-Emissions-And-Some-Em-N-Em---And-Em-S-Em--Heterocyclic-Polycyclic-Aromatic-Hydrocarbons-2013; National Institute for Occupational Safety and Health (NIOSH). “Hazard Review: Health Effects of Occupational Exposure to Asphalt.,” December 2000. doi.org/10.26616/NIOSHPUB2001110.
 Based on U.S. EPA Toxics Release Inventory Data for releases of polycyclic aromatic compounds from asphalt plants in 2020.
 Cash, Carl G. “The Relative Durability of Low-Slope Roofing.” In Proceedings of the Fourth International Symposium on Roofing Technology, 119–24, 1997.
 US Occupational Safety and Health Administration, “OSHA Fact Sheet: Do You Have Work-Related Asthma? A Guide for You and Your Doctor,” March 2014, https://www.osha.gov/Publications/OSHA3707.pdf; Kenneth D. Rosenman, Mary Jo Reilly, and Barton G. Pickelman, “2019 Annual Report Tracking Work-Related Asthma in Michigan” (Michigan State University, July 20, 2020), https://oem.msu.edu/images/annual_reports/2019-WRA-Annual-Report-FINAL.pdf; Daniel Lefkowitz et al., “Isocyanates and Work-Related Asthma: Findings from California, Massachusetts, Michigan and New Jersey, 1993-2008,” American Journal of Industrial Medicine 58, no. 11 (November 2015): 1138–49, https://doi.org/10.1002/ajim.22527; While reported incidences have declined in recent years, limited data are available to gauge the scope of the issue.
Last updated: February 22, 2022