Kitchen exhaust grease is eating a TPO roof: how to protect membranes around restaurant fans

The roofer who shared the picture on Sunday said he was surprised the roof was not leaking inside yet. Inspectors know the pattern. InterNACHI's inspection narrative library says animal fats break TPO down chemically, leaving it soft and blistered with seams that open and leak. EPDM and asphalt roofs fare no better: cooking grease makes both swell and lose their ability to shed water.

GAF's chemical resistance guide for its single-ply membranes says TPO soaks up grease and oil and stains. In the guide's rating table, TPO gets a B, meaning limited absorption, for grease and for animal and vegetable fats, and a C for oils. Standard PVC scores a C on grease. Only PVC-KEE earns an A, and GAF names it the better choice where grease and oil will reach the roof. Where TPO goes on a job with light chemical exposure, GAF suggests a second, sacrificial layer around stacks, vents and grease traps. The same guide says GAF's limited warranties do not cover damage from chemical attack, with grease and oil named.

The fire code reaches the roof as well. NFPA 96, as excerpted by ventilation supplier HoodFilters.com, requires rooftop exhaust terminations to drain grease from low points in the fan or duct into a closed, rainproof, noncombustible container built for the service. Each upblast fan needs a drain to a grease receptacle that is easy to see and reach and holds 1 gallon at most. Collection devices may not hurt fan performance, and listed systems are tested to UL 710A.