Here is some general guidance to use when choosing roofing membrane materials for flat or low-slope roofs:
- 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).
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:
- Prefer thermoplastic polyolefin (TPO) roofing membranes. These products have the fewest chemical hazards.
- If using a single-ply roofing membrane, avoid polyvinyl chloride (PVC). Standard PVC membranes contain large quantities of orthophthalate plasticizers that are known to leach out of the products. While some newer PVC membranes (referred to as ketone ethylene ester or KEE) contain an alternative plasticizer that is less likely to leach from the membrane, they may still contain some orthophthalates. Both types of products are made with a large amount of PVC, and the PVC production process requires more hazardous chemical building blocks than TPO and EPDM roofing membranes.
- Prefer mechanically fastened or ballasted systems over fully-adhered systems. Both solvent-based and water-based adhesives used to install fully adhered membranes contain a number of hazards that can be avoided by eliminating the use of adhesives altogether.
- 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. While all adhesives typically contain hazardous content, water-based adhesives contain far less than solvent-based adhesives. Low-VOC solvent-based adhesives can contain large amounts of chemicals that are suspected carcinogens even though they aren’t VOCs, so they are still less preferable than water-based adhesives.
- Ask for disclosure of any flame retardants, and avoid products containing halogenated flame retardants. Most types of membranes require the use of flame retardants, and these are not always well disclosed. Both halogenated and non-halogenated flame retardants may be used in roofing membranes. Ask for disclosure of flame retardants, and prefer products containing non-halogenated flame retardants.
- Avoid applying silicone coatings or coatings containing per- and polyfluoroalkyl substances (PFAS), such as PVDF (polyvinylidene fluoride), to roofing membranes. Silicone-based coatings contain chemicals called cyclic siloxanes that are considered persistent, bioaccumulative toxicants, meaning they do not easily break down in the environment and tend to accumulate in living things. PFAS are persistent, and can be bioaccumulative and/or toxic to humans and ecosystems. Some well-studied PFAS with known health effects have been phased out, but similar concerns exist for their replacements. If it is necessary to apply a coating, avoid silicone-based coatings and always ask for confirmation that other coatings do not contain PFAS.
- If opting for asphalt-based roofing, choose modified bituminous membranes over conventional built-up roofing (BUR). While all asphalt-based products contain carcinogenic compounds, traditional BUR products require the use of a much larger amount of asphalt.
- Avoid PMMA fluid-applied and spray polyurethane foam roofing. Along with asphalt-based roofing, these products contain the most hazards to human and environmental health.
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.
- Asphalt Primer for Built-Up Roofing
- Cold fluid-applied PMMA waterproofing
- High-Solids Silicone Roof Coating
- Hot-Applied Asphalt Waterproofing/Roofing
- Low-VOC Solvent-based TPO/EPDM Roofing Membrane Adhesive
- Modified Bituminous SBS Membrane Roofing
- Reinforced EPDM Roofing Membrane
- Reinforced PVC Roofing Membrane
- Reinforced Thermoplastic Polyolefin (TPO) Roofing Membrane
- Solvent-based Single-ply Roofing Membrane Adhesive
- Spray Polyurethane Foam (SPF) Roofing
- Torch Applied APP Bitumen Roofing
- Water-based Single-ply Roofing Membrane Adhesive
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 Based on U.S. EPA Toxics Release Inventory Data for releases of polycyclic aromatic compounds from asphalt plants in 2020.
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Last updated: February 22, 2022