Grease on the roof around the exhaust fan

Grease staining spreading out from the exhaust fan across your roof is not cosmetic and it is not normal. It is a containment failure, and it usually ends up on the tenant’s bill.

What is actually happening

A commercial kitchen exhaust fan does exactly what it is supposed to do: pull grease-laden vapour off the cook line and discharge it outside. What it cannot do is decide where the grease goes once it is out there.

Some of it leaves as vapour. The rest condenses on the fan housing, the curb, and the roof surface around it, and then spreads with rain and heat. Without a containment system at the fan, every service hour puts more of it on your roof.

Why it matters more than it looks

It degrades the roof. Grease is not kind to most commercial roofing membranes, and the damage accumulates quietly until it is a roofing job rather than a cleaning one. This is the expensive version of the problem.

It is a safety issue. A greased roof is genuinely slippery, and the people who have to walk it are your service contractors, your HVAC technician, and whoever inspects it.

It is usually a lease violation. Most commercial restaurant leases put the exhaust system and any damage from its operation on the tenant. You will typically find out about this when the landlord does, which is later and more expensive than finding out now.

What fixes it

A grease containment system at the fan. A properly sized unit at the fan base with absorbent media that catches condensate before it reaches the membrane.

Changing the absorbent on a schedule. This is the part people miss. Containment is a consumable system, not a fixture. Saturated absorbent catches nothing, so a containment box that has not been serviced in two years is doing the same job as no containment at all, while giving everyone the impression the problem is handled.

A hinge kit on the fan, if there is not one already. A fan that cannot be lifted off its curb cannot be cleaned underneath, and that is where the worst of it sits. Hinge kits run $150 to $300.

Cleaning the existing deposit off the roof surface, carefully, without making a drainage problem out of it.

Fargo conditions

Fargo’s cold is the complication. Grease that leaves the cook line as vapour stiffens fast as it moves away from the heat, so in winter it sets hard at the far end of the duct and around the fan rather than draining back. That means the rooftop end of a Fargo system is frequently the dirtiest part while the canopy looks fine, and it means a roof that is safe to work in September is a different proposition in January.

How this connects to the rest of the system

Rooftop grease is usually a symptom rather than an isolated fault. A system that is putting a lot of grease on the roof is often one where the ductwork is not being cleaned to bare metal, the filters are inadequate or saturated, or the cleaning interval is longer than what you cook justifies. The NFPA 96 frequency guide sets out what your category actually requires.

If your last several cleanings produced no photographs from the fan or inside the duct, it is worth asking what was actually cleaned.

What it costs

Published on the pricing page.

Get it looked at

Photograph the fan and the roof around it if you can do so safely, and tell us whether there is any containment fitted and when the absorbent was last changed. The service area is Fargo, West Fargo, Horace, Casselton, and Grand Forks.