Restaurant Grease and Roof Membrane Damage
If your building has a commercial kitchen, the exhaust fan on the roof is quietly doing more damage to your roofing than the weather is. Grease-laden vapor condenses on the roof surface around the exhaust curb, and most single-ply membranes have very little resistance to it.
This is a narrow problem with a straightforward solution, and it is one of the more common reasons we see a five-year-old roof needing work in one specific area.
What grease does to a roof
The mechanism depends on the membrane, and the differences are significant:
- TPO and EPDM. Both are vulnerable to animal and vegetable fats and oils. Grease acts as a plasticiser, softening the membrane, and over time it swells, loses tensile strength and becomes prone to splitting. EPDM is particularly susceptible.
- PVC. Considerably more resistant to grease and oils, which is why it is frequently specified on restaurant and food-processing buildings. Not indestructible, but a materially better choice.
- Modified bitumen and built-up roofs. Asphalt-based products are softened and dissolved by petroleum and cooking oils. Grease exposure degrades them steadily.
- Coatings. Vulnerable, and generally not a solution to a grease problem.
Alongside the chemical attack, grease creates a secondary problem: it is slippery, it collects grit and debris, and it makes the area around the exhaust genuinely hazardous for anyone working on the roof.
The warranty issue
This is the part that catches building owners out. Manufacturer warranties on single-ply membranes commonly exclude damage from grease, oils, fats and solvents, and some require specific protection around kitchen exhausts as a condition of coverage.
So the sequence goes: grease damages the membrane, the membrane splits, water gets into the assembly, a warranty claim is made, and it is declined as chemical damage rather than a material defect. The repair falls entirely on the owner. Terms vary by manufacturer and system, so it is worth reading your own warranty documents specifically for the chemical exclusion.
What proper containment looks like
The solution is to stop grease reaching the membrane at all, and it has three parts:
- A grease containment system at the exhaust fan. A purpose-made unit fitted at the fan that captures grease before it discharges onto the roof, with absorbent media that gets changed on a schedule. This is the primary defense and it is inexpensive relative to a roof repair.
- A sacrificial protection pad around the curb. A grease-resistant membrane or walkway pad installed over the roofing in the affected zone, which takes the exposure instead of the roof and can be replaced when it degrades.
- Regular cleaning. Even with containment, some accumulation happens. It needs removing with products compatible with the membrane, the wrong solvent does its own damage.
Where a building has a persistent grease problem and a roof due for replacement, specifying a PVC system is worth considering on the basis of chemical resistance alone.
Signs the roof is already affected
- Visible discolouration or dark staining spreading outward from the exhaust curb.
- Membrane in that area feeling soft, tacky or noticeably different underfoot from the rest of the roof.
- Swelling, blistering or wrinkling localised around the exhaust.
- Splits or cracks in the affected zone, particularly along seams.
- Grease residue in the gutters, scuppers or drains downstream of the exhaust.
- A slippery surface that persists after rain.
Because the damage is confined to a defined area, it is usually repairable as a section rather than requiring a full replacement, provided it is caught before water has been getting into the insulation for a long period. An infrared scan establishes whether moisture has already spread beyond the visibly damaged area.
Who is responsible for what
This one causes real friction, particularly in leased buildings. Kitchen exhaust cleaning is typically a tenant obligation under a lease and is often required by fire code and insurance. Roof maintenance is more commonly a landlord obligation. Grease damage sits precisely between the two.
The practical answer is to establish in writing who fits and services the containment system, who cleans the roof surface, and who bears the cost of grease-related roof repair. Lease terms and local requirements vary considerably, so this is a question for your lease and your attorney rather than for us, but leaving it undefined reliably produces a dispute. Landlord or tenant roof responsibility covers the wider version of this problem.
Where this comes up for us
Restaurants obviously, but also hotels, schools, hospitals, care homes, corporate cafeterias, food processing facilities and any multi-tenant retail building with a restaurant unit. In multi-tenant buildings it is often the neighbouring tenant’s roof section that suffers, depending on prevailing wind and fan placement.
Our commercial repairs team handles grease-damaged sections, and grease exposure is one of the specific items we look at during preventative maintenance visits, it is a problem that responds far better to being caught early than to being discovered as a leak. Inspection frequency should be higher on buildings with kitchen exhausts.
Grease and roofing questions
Yes. Grease acts as a plasticiser on TPO and EPDM, softening the membrane so it swells, loses strength and eventually splits. Asphalt-based systems are dissolved by cooking oils. PVC is considerably more resistant, which is why it is often specified on restaurant buildings.
Commonly not. Manufacturer warranties on single-ply systems frequently exclude damage from grease, oils, fats and solvents, and some require protection around kitchen exhausts as a condition of coverage. Read your own warranty documents for the chemical exclusion specifically.
A purpose-made unit fitted at the exhaust fan that captures grease before it discharges onto the roof, using absorbent media replaced on a schedule. It is the primary defense and costs very little relative to repairing a damaged roof section.
Look for discolouration spreading outward from the exhaust curb, membrane that feels soft or tacky underfoot compared with the rest of the roof, localised blistering or wrinkling, splits along seams in that zone, and grease residue in drains downstream.
PVC, on chemical resistance grounds. It handles grease and oils considerably better than TPO, EPDM or asphalt-based systems. On a building with a persistent grease problem and a roof due for replacement, that resistance is worth specifying for.
It sits between the two, which is why it causes disputes. Exhaust cleaning is usually a tenant obligation and roof maintenance usually a landlord one. Establish in writing who fits and services containment, who cleans the roof, and who pays for grease-related repairs. Lease terms vary, so ask your attorney.