Effects of Greases, Oil and Chemicals on Low-Slope Roofing Materials

Did you know that greases, oil and chemical effluents can be even harder on your roof than the weather?  Roofing systems are intended to provide protection from natural elements such as rain, snow, hail, sleet, etc.  Low-slope roofing systems that are properly designed, installed and maintained should provide the user with satisfactory protection from these elements. However, some roofing systems, especially those on factories, restaurants and fast food chains, may require special care in design due to the presence of greases, oils, bacteria and/or other agents on the roof surface that tend to adversely affect the integrity of the roof membrane. Understanding the ways in which contaminants can affect your roof is your best defense against them.

Effects of Oils and Greases

Most low-slope organic roofs can be adversely affected by exposure to cooking oils (animal or vegetable) and greases. For modified bitumen systems, membrane degradation typically occurs around exhaust vents, where the roofing membrane has repeated contact with these contaminants. The organic substances contained within the above contaminants typically weaken and eventually break down the polymer-bitumen network, causing premature degradation of the roof.

Effects of Bacteria and Fungi

Factories producing foods such as potato pulp and dry milk have reported cases of modified bitumen membrane decay due to bacteria. Such deterioration, which usually starts as “mud cracking,” may ultimately lead to the total decay of the organic roof and any surface coating. The degree of degradation is dependent upon the type of microorganism, the composition of the bitumen and temperature and other climatic conditions. Fungus growth, which typically occurs in hot, humid regions, does not cause the same detrimental effects as bacterial attack and usually poses only aesthetic concerns.

Effects of Other Chemicals

Other chemicals, such as solvents, acids, bases and oxidizing agents, can cause varying degrees of harm to polymer-modified bitumen roofing and other organic low-slope systems. Non-polar solvents can temporarily swell and soften polymer-modified bitumens, causing slumping and poor traffic resistance. They can also cause the polymers to “separate” from the asphalt. While polymer-modified bitumens have excellent resistance to various inorganic acids and bases, some of these chemicals may attack and degrade glass and polyester mats, as well as fillers, such as talc and limestone. Organic acids, such as acetic acid, are also known to have detrimental effects. Strong oxidizing agents can attack both the polymer and the bitumen in a membrane. In addition, when ponding water is present, inert solid dusts can contribute to “mud cracking.” All of these effects may lead to premature failure of the roofing membrane.

Recommendations for Containing Contaminant Exposure

  • Wherever possible, reduce or eliminate exposure to contaminants.
  • Determine the types and concentrations of contaminants that may be present on the roof. When re-roofing, investigate what effects, if any, contaminants present had on the existing roof before specifying and applying a new roofing system.
  • Use commercially available traps and/or filters to prevent contaminants from being exhausted onto the roof.
  • Establish a roof maintenance program to monitor affected roof sections and to properly maintain traps or filters.
  • Provide positive drainage (i.e., at least 1/4” per foot roof slope) to prevent ponding in the affected area.
  • If contaminant effects are minor, increase the number of plies and/or add resistant coatings to provide adequate protection.
  • Investigate alternate venting designs that minimize or eliminate contamination of the roofing membrane.