A high-rise roof in Riverdale takes more wind than a walk-up in the middle of Tremont, and the membrane has to be chosen for that exposure first. A property manager should check the edge and the attachment before the product name, because wind starts at the perimeter. Sika Sarnafil is a roofing manufacturer known for welded thermoplastic membranes, mostly PVC-based, together with liquid-applied flashing and waterproofing products from its parent company. These categories get installed and repaired on Bronx buildings and matched to the exposure.
Welded Thermoplastic Membranes
A thermoplastic membrane is a factory sheet whose seams are fused by hot air, not glued or taped. A properly welded seam is as strong as the sheet itself. The surface is usually white or light gray and reflects heat. The sheet resists many chemicals, oils and greases, which matters on roofs where kitchen exhaust, process vents or grease traps discharge.
Welded seams make the sheet watertight in a way that taped seams cannot easily match, but only if the welds are made right. We probe every seam after welding, mark open laps and reweld before the crew leaves. Probing seams is part of daily practice, not a final check.
Color and age change how a thermoplastic behaves. A white sheet reflects most of the sun and stays cooler than a dark one, which slows aging. Over years the surface collects dirt, and a rinse restores much of the reflectivity. A sheet that has stiffened and cracked at the folds is at the end of its life, and no cleaning will bring it back.
High-Rise and Exposed Roofs in Riverdale
Some of the highest ground in New York City is in Riverdale, bounded on the west by the Hudson River, so its roofs take open wind. High-rises gather in Spuyten Duyvil, and central Riverdale has added mid and high-rise condominiums since 2005. A tall building sees stronger gusts at the roof than a low one does, and the corners and perimeter see the strongest of all.
For roofs in Riverdale we pay close attention to perimeter attachment, edge metal gauge and fastener spacing. A fully adhered or mechanically attached thermoplastic can be designed for high wind zones, with closer spacing at corners and edges. We confirm the design wind pressure with the building's engineer or the applicable code before specifying the attachment.
High roofs also get cold. Wind chill does not affect the membrane, but freezing rain and ice can pile at parapet drains and scuppers, so we keep outlets large and clear. On a tall building, access for repairs is harder, which is another reason the first install should be right.
Exhaust, Grease and Chemical Exposure
Some membranes soften and swell when hot grease lands on them. Restaurant roofs, commercial kitchens and food-processing buildings put grease on the roof through exhaust fans. A thermoplastic with chemical resistance holds up better, and a grease containment pan under the fan helps any membrane. We look at what leaves the building and where it lands.
The Cooperative Market at Hunts Point has 700,000 square feet of refrigerated space, and food and cold-storage buildings in industrial areas like Hunts Point can have exhaust and refrigeration discharge on the roof. Where the exposure warrants it, a chemical-resistant membrane and protected walk paths belong in the scope.
Liquid-Applied Flashing and Waterproofing
Details are where a flat roof fails, and some details do not suit a cut-and-weld sheet. A cluster of pipes, an odd curb, a drain bowl at a wall corner or a parapet with a rough surface are hard to flash with pre-cut parts. A liquid-applied flashing resin, reinforced with fabric, cures into a continuous layer that follows the shape.
We use liquid-applied flashing where it fits, and where a detail has failed repeatedly with other methods. It is also used for small repairs on aged roofs where welding is not possible. The resin type must be compatible with the membrane, and we confirm that before application. Every pipe, curb and hatch is a penetration flashing detail, and each gets the method that suits its shape.
Retail Corridors and Large Roofs
A Business Improvement District manages the Fordham Road corridor, which the borough counts as its longest. Roofs along a corridor like that carry rooftop units, signs and exhaust, and a welded white membrane is one option for the main field. Gateway Center sits at Bronx Terminal Market on 17 acres next to the Major Deegan Expressway, and large retail roofs share concerns of access, equipment and drainage.
The decision between thermoplastic and other families comes down to what the roof carries, how it drains, how often people walk on it and what the budget allows. We lay out each in the proposal.
On a retail roof, a white welded sheet also reduces the cooling load of the units below, and its seams hold up to frequent service traffic when walk pads protect the routes. We install pads from the hatch to each unit before the crew leaves, and we mark the pads on the roof sketch.
How We Install and Repair
We install to the manufacturer's published requirements for the system chosen, with documented seam testing, flashing inspection and photographs of every stage. Whether a warranty is available is for the owner and the manufacturer's program to settle, and the scope lists the requirements. Our warranty management work keeps the file in order.
Repairs on existing thermoplastic follow cleaning, then hot-air welding of patches and flashings with compatible material. An aged sheet takes a weld only after the surface is cleaned, and we test every patch.
Weather, Cost and Code
Every new membrane brings a drainage review, because Ida's record 3.15 inches in an hour in September 2021 tested every drain. A welded sheet handles Central Park's 95.7 F July average and -15 F record low with proper detailing. Price follows area, tear-off, insulation, wind design, penetrations and access. The Department of Buildings provides the 2022 NYC Construction Codes. Check filings with them. We compare with other makers, such as Duro-Last and Carlisle SynTec, when owners want options. Seam widths are measured on every run, not only where a probe finds a problem.
Commercial Roofing Questions
Is a welded seam really stronger than a taped seam?
A good weld fuses the sheets into one, and the seam can match the strength of the sheet. A taped seam relies on adhesive. Both work when made correctly, and both fail when made on a dirty surface. We probe all seams either way.
What wind speed can a thermoplastic roof take?
The attachment design, the building height and the code requirements set the answer. We confirm the design wind pressure for the building and specify attachment to meet it. No sheet withstands wind on its own without proper edge details.
Can grease from a restaurant fan damage the roof?
Yes. Some membranes soften with grease. A chemical-resistant sheet and a grease pan under the fan reduce the risk. We look at the fan location and the discharge path.
Does liquid flashing last as long as the sheet?
It can, if the resin is compatible, reinforced and applied at the specified thickness. Poor preparation is the usual cause of failure. We clean and prime every substrate, and we inspect the cured layer.
Can an aged PVC roof be recoated?
Some coatings bond to cleaned thermoplastic, but the surface sets the outcome. We test a small area first and check the insulation for moisture before recommending anything.
Send the Building Type, Height and Roof Age
Tell us the building type, the roof age and the last tenant complaint, and ask for a flat-roof walk before anyone writes a scope. For a tall building, include the number of floors.
Request a Roof Assessment