A seafood restaurant roof and a hospital wing have one thing in common, and it is not the building. It is what comes out of the exhaust. Kitchen fans throw grease onto the sheet, laboratory and air-handler exhaust adds vapors, and a membrane never designed for either softens first around the fans, then at the seams. PVC is the single-ply sheet formulated to take that treatment, and a property manager with food service tenants, laboratories or medical air handlers should ask about it before any other membrane is priced. The first step is a walk of the exhaust area, because that is where the roof announces what it can survive.
We install, weld, repair and replace PVC on low-slope commercial roofs in the Bronx, NY, and when a cheaper sheet fits the roof, the proposal says so.
What PVC Is and Is Not
PVC is a thermoplastic sheet in the same family as TPO, but it is compounded with plasticizers and stabilizers that resist grease, oils and many chemicals. Seams are welded with hot air into one continuous membrane. Reinforced with a polyester or fiberglass scrim and usually white or light gray, the sheet goes down mechanically attached, fully adhered or ballasted, depending on the roof.
It costs more than most single-ply sheets, and over a long service life the plasticizers can migrate out and stiffen the membrane. It also objects to some neighbors. Old asphalt and some foam insulations eat into PVC on contact, which is why a separator layer goes wherever the sheet meets something incompatible. Match thickness to traffic. Frequent service visits to equipment call for a heavier sheet with walk pads, and a roof that is visited rarely can use a lighter sheet. The proposal states the thickness so bids compare fairly.
City Island Kitchens and Salt Air
Most of the businesses on City Island sit along City Island Avenue, and they include seafood restaurants. The island lies at the western end of Long Island Sound, so a restaurant roof there takes kitchen exhaust and open wind exposure together. Neither fact says what any one building carries, but the combination is the one that makes PVC worth pricing against the alternatives. A hardware store, a small supermarket and a bank share the street with the restaurants, so neighboring roofs can carry very different exhausts.
Winter tests the same sheet from the other direction. The Central Park station has a record low of -15 F, and an aged PVC sheet that has lost plasticizer will crack at its folds in a hard freeze. A roof showing that crazing needs flashing failure repair at the folds before the next winter, not after it.
Hospital and Laboratory Roofs
Montefiore has Bronx campuses in Norwood, Morris Park and Wakefield, and the eastern edge of Morris Park holds the Albert Einstein College of Medicine, Jacobi Medical Center and the Jack D. Weiler Hospital division. A hospital roof carries exhaust, laboratory ventilation and sensitive intake equipment, and the membrane chosen for it has to tolerate that exposure.
Work on a medical roof is scheduled with the facility staff. Intakes are covered while seams are welded, and a heat-welded sheet avoids the adhesive fumes that could be drawn into a building full of patients. Units that must keep running stay running; the crew flashes around them and plans each lift with the building engineer.
Reading the Sheet
Start at the exhaust. We look for softened, sticky or discolored sheet within several feet of every fan and test how flexible it is at the folds. Seams come next: every weld is probed, with extra attention near drains. Flashing at walls and curbs is checked for stiffness and shrinkage, and where we can see the underside, dark patches in the insulation point to moisture.
We photograph each fan zone with a tape measure in frame, so a change between visits can be measured. Grease follows water, so on a roof that drains toward a kitchen exhaust the slope and the drains matter as much as the sheet. A broken or missing grease pan lets runoff reach the membrane, and the pan is on the work order as an item of its own.
Repair, Recover or Replace
A young PVC roof with local damage gets the damaged area cut out, new sheet welded in and the flashing replaced. Once the sheet has stiffened across the field, patches stop holding, and a commercial roof replacement becomes the better spend. With dry insulation and a sound structure, a PVC recover over the old roof is possible, using a separator sheet to protect the new membrane.
Against TPO, PVC resists grease and chemicals better and costs more, so a roof without kitchen or laboratory exhaust may do fine with TPO. For harsher exposure, KEE adds another layer of chemical resistance, and we price it where the exposure warrants. Crushed or wet polyiso gets replaced under any of them, and a cover board shields the new sheet from foot traffic near the fans.
Working Beside Live Exhaust
Over a kitchen, the crew agrees a schedule with the cook staff so the fans never stop at the lunch rush. Restaurant roofs get worked before service opens, fans bagged, and any tenant complaint during the job goes straight to the site lead. A welded, adhesive-free method keeps fumes away from the intakes wherever the design allows it.
PVC welds in dry weather at moderate temperatures. Cold slows the work and asks for extra care at the seams, and heat makes the sheet limp, so most jobs run from spring to early fall. Open sheet is covered and sealed at the end of each day, and the crew checks the forecast against the plan.
Closeout and Maintenance
We hand over a seam map, photographs of each exhaust zone and a short list of grease containment items to empty on a schedule, since a full pan harms the sheet more than weather does. Work around marinas on City Island can add limits on deliveries and hoisting, so those windows are set early. The Department of Buildings provides the 2022 NYC Construction Codes. Paperwork starts there. Send the building type, the roof age and where the exhaust sits, and we will walk it. Ask the supervisor to show the probe log at each visit.
Commercial Roofing Questions
Why does grease ruin some roofs and not others?
Grease and oil break down the plasticizers and polymers in many membranes, so the sheet softens, swells and weakens. PVC's compound resists that attack, so it is the usual pick beside a commercial kitchen fan.
Can PVC be laid over an old asphalt roof?
Yes, provided dry insulation sits underneath and a barrier layer keeps the PVC off the asphalt, which can damage it. A moisture survey comes first.
Is PVC worth its price on a roof with no kitchen?
Frequently not. A roof that sees no grease, chemicals or hot exhaust may be well served by a cheaper single-ply, and both prices go in the proposal.
What does a Bronx winter do to a PVC sheet?
New sheet handles cold well. Age is the problem: PVC that has lost plasticizer turns stiff and can crack along folds and around drains and flashings.
How are PVC repairs made?
The area is cleaned, damaged sheet is cut out and a matching patch is welded in with hot air. Old, contaminated PVC may not weld cleanly, so a small test area goes first.
Tell Us Where the Exhaust Sits
Send the building type, roof age and the location of kitchen or lab exhaust. We will walk the flat roof, test the sheet near every fan and send a written answer on repair versus replacement.
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