Chemical Resistance of Single-Ply Membranes
For most roofing projects, chemical resistance of the membrane is not a consideration. However, in a few cases, the roof can be exposed to chemicals, oils, greases, and the like. In these situations, the right membrane must be chosen. If chemical resistance is required, it must be balanced against other key factors that must be satisfied in order to meet all the requirements of the specific project. These may be factors such as UV and heat resistance, ease of installation, heat seam-ability, warranty requirements, etc.
In general, emissions and releases of chemical materials from industrial and commercial operations are tightly regulated and should never be a concern for a building’s roof. In fact, membrane specifications do not include any requirements for chemical resistance. However, membrane suppliers do occasionally get asked for guidance. Building owners sometimes have concerns about such things as cleaning materials, oil, grease spills from grease traps, and “fumes.”
Although there are differences between membranes, the chemical verification and design responsibility remains with the architect, specifier, engineer, or roofing contractor of record to determine that the project-specific conditions are compatible with any roof membrane. Membrane manufacturers including GAF do not guarantee, warrant, or cover damage due to oil, greases, or chemicals.
TPO: The “all around” membrane
TPO roofing membranes have a very good balance of properties. Heat and UV resistance is excellent, ease of welding and seam strengths are very good, and overall value is very high. Warranties of as long as 35 years can be obtained for the best grades. However, exposure of TPO to acids can cause it to weather faster than normal. It can absorb greases and oils, but becomes stained in the process.
If TPO is being used for a job that might see some light chemical exposure, the application of a second “sacrificial” layer around sources of chemicals could be considered. These could include grease traps, vents, and stacks.
PVC: The flexible membrane
PVC roofing membrane is more flexible than TPO and is sometimes preferred due to its ease of handling. It is more acid resistant than TPO and is often recommended for roofs that might be exposed to grease and oils. However, greases and oils will often “draw out” the plasticizers from the sheet and cause hardening and embrittlement of the membrane.
PVC-KEE: For improved resistance
When considering heat-weldable single-ply membranes, PVC-KEE is widely regarded as having the best chemical resistance. It is resistant to a broad range of chemicals and solutions, making it a better choice in applications that will have chemical exposure. However, as noted in the next section, the degree of exposure, the area of exposure, and the frequency of exposure will increase the effect on the membrane.
Project-Specific Chemical Resistance
Obviously, the degree of chemical attack on any material will be influenced by a number of factors and their interactions.
- Some combinations of chemicals will generally be considered more harmful to the membrane than the individual chemicals.
- Increasing the concentration of chemicals increases the effect on the membrane.
- Higher temperatures increase the effect on the membrane.
- The degree of exposure, the area of exposure, and the frequency of exposure will increase the effect on the membrane.
In general, roofs should not be exposed to chemicals on a frequent basis. In fact, the first question that should be asked if a building owner has a concern is how to eliminate or reduce the risk of chemical release from the building. If a roof is being exposed to chemicals, it might be a sign of broader, more serious issues.
However, leaks from grease traps, occasional releases of chemical mists, etc., can occur. Strong acids of any type, oxidizers, and most strong bases are known to cause issues with most roofing membranes regardless of type. It is important to note that the degree of attack on any material is influenced by a number of variable factors, including concentration of the chemical, temperature, aeration, duration of exposure, stability of the fluid, possible chemical reaction with other compounds in the area, etc.
If a building owner has concerns, these should be addressed by the architect, specifier, engineer, or roofing contractor to determine that the project-specific conditions are compatible with any roof membrane.