When it comes to selecting a roofing system, the type of membrane you choose can play a big role in reducing both a building’s energy consumption and its contribution to the urban heat island effect. But have you ever thought about how your choice of roofing membrane can impact human health and the environment? HBN recently released guidance for choosing safer Low-Slope Membrane Roofing products. 

Why this matters
Since roofing membranes are exterior products and are not located on the inside of buildings where occupants are spending their time, they may seem like a lower priority concern when it comes to their chemical makeup. Nevertheless, chemicals in roofing membranes can still impact human and environmental 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. 

It’s also important to remember that the materials we choose have impacts outside of the indoor environment. Chemicals are known to leach out of roofing membranes and can contaminate surface water. Roofing membranes are also manufactured in ways that can affect communities living near these facilities when chemicals are released into the air and water in their surroundings.[1]

Low-slope Roofing Product Guidance

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HBN reviewed the chemicals and materials used to make different roofing membranes, their upstream manufacturing concerns, and exposure potential to shape our product guidance around roofing membranes. When all of these factors are considered, no type of roofing that we reviewed was entirely free of chemical hazards. Some, however, had more concerns associated with them than others.

Thermoplastic polyolefin (TPO) membranes contained the fewest chemical hazards, and also had fewer exposure concerns related to installation. Generally, fewer hazardous chemicals are required to make TPO than are required to make the base materials used for other types of membrane roofing.[2] Similar to other types of single-ply membranes, these membranes can be mechanically fastened, which avoids the hazards associated with adhesives that are used in fully adhered applications. 

Spray polyurethane foam roofing, cold fluid-applied polymethyl methacrylate (PMMA), built-up roofing (BUR), and modified bituminous roofing were ranked lowest on the hazard spectrum. These products contained the most hazardous chemicals and presented the most exposure concerns for installation teams. Likewise, polyvinyl chloride (PVC) membranes are not recommended because, in addition to hazardous materials used and released during raw material manufacturing, they contain orthophthalate plasticizers that are known to leach out of the membrane[3] and are associated with multiple health hazards.[4] The base materials that go into all of these types of membranes also tend to be made with more hazardous chemicals than are required to make TPO.  

Occupational Exposures
In general, products that are wet-applied are ranked lower in the membrane roofing category. These products have the greatest potential to expose installation teams and people nearby to hazardous chemicals. For instance, while built-up roofing (BUR) may last longer than most single-ply roofing membranes, it exposes installation teams to bitumens. Occupational exposure to bitumens and bitumen fumes during roofing has been identified to be “probably carcinogenic to humans” by the International Agency for Research on Cancer (IARC).[5] Spray polyurethane foam roofing exposes installation teams to chemicals called isocyanates, which the US Occupational Safety and Health Administration (OSHA) has identified as a leading cause of work-related asthma.[6]

In addition to the type of material used for roofing membranes, we also considered where health and environmental impacts may occur with some types of adhesives and primers. These accessory products are important because they also impact even the highest ranked product types in our guidance.

If a fully adhered membrane is necessary, then water-based adhesives should be preferred over solvent-based adhesives, even if the latter are low-VOC. Solvent-based, low-VOC roofing adhesives can still contain large amounts of chemicals that are suspected carcinogens, so it is best to avoid them. 

Fenceline Impacts
Last October, we wrote about the hidden costs of many building materials that often fall disproportionately on communities of color and low-income communities who live and work in close proximity to facilities manufacturing building materials and their ingredients. Materials that are made using more hazardous chemicals can potentially have a greater impact on these fenceline communities. In the roofing membrane product guidance, this translates to materials made with PVC and asphalt being ranked lower than materials made with TPO or EPDM rubber. 

Roof Runoff
Chemicals don’t always stay in the roofing membrane. Some can leach out of products when they are exposed to rainwater. 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 chemicals are known to leach out of membranes and accumulate in runoff water along with other chemicals that deposit on the membrane from the atmosphere.[8] Consequently, we recommend using membranes that contain fewer hazardous chemicals, which in turn will likely release lower levels of hazardous chemicals into the environment.

The Key Takeaways
Use the guidance below to guide your product decisions and conversations with manufacturers:

  • Prefer thermoplastic polyolefin (TPO) roofing membranes.
  • If using a single-ply roofing membrane, avoid polyvinyl chloride (PVC).
  • Prefer mechanically fastened or ballasted systems over fully-adhered systems.
  • If specifying fully adhered roofing, check with manufacturers to determine if water-based adhesives can be used with the roofing system and prefer them over other adhesives.
  • Ask for disclosure of any flame retardants, and avoid products containing halogenated flame retardants.
  • Avoid applying silicone coatings or coatings containing per-and polyfluoroalkyl substances (PFAS), such as PVDF (polyvinylidene fluoride), to roofing membranes.
  • If opting for asphalt-based roofing, choose modified bituminous membranes over conventional built-up roofing (BUR).
  • Avoid PMMA fluid-applied and spray polyurethane foam roofing. 
  • Prefer products with full disclosure of content through Health Product Declarations (HPDs).

Conclusion
Roofing membranes are only one part of a roof, but they are an important part of a building’s overall performance and its contribution to climate change. When specifying flat or low-slope roofing it is also important to consider the roofing membrane’s impact on human health and the environment. The next time you specify flat or low-slope roofing, you can use this Product Guidance to navigate conversations around selecting a system that has the fewest known impacts to human health and the environment.
 


Footnotes

[1] 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.

[2] Ann Blake and Mark Rossi. “Plastics Scorecard.” Clean Production Action, July 1, 2014. https://www.cleanproduction.org/resources/entry/plastics-scorecard-resource.

[3] 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.

[4] 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.

[5] 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. https://doi.org/10.26616/NIOSHPUB2001110.

[6] 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. 

[7] Based on U.S. EPA Toxics Release Inventory Data for releases of polycyclic aromatic compounds from asphalt plants in 2020;
Vallette, Jim. “Chlorine & Building Materials Project: Phase 1 Africa, The Americas, and Europe,” July 2018. https://healthybuilding.net/reports/18-chlorine-building-materials-project;
Vallette, Jim. “Chlorine & Building Materials Project: Phase 2 Asia Including Worldwide Findings,” March 2019. https://healthybuilding.net/reports/20-chlorine-building-materials-project-phase-2-asia-including-worldwide-findings
Ann Blake and Mark Rossi. “Plastics Scorecard.” Clean Production Action, July 1, 2014. https://www.cleanproduction.org/resources/entry/plastics-scorecard-resource.

[8] 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.