Commercial Roofing
A white seam that has opened a hairline after a long hot summer, with a dark stain on the ceiling several bays away, is how a TPO roof usually reports a weld that has let go. In Edinburg, TX, the weather service's heat-safety months (May to October) overlap most of the tropical rain season, so a single-ply membrane has to hold its welds through months of sun and then stay watertight under a downpour.
TPO, short for thermoplastic polyolefin, is a pale, reflective single-ply sheet that is welded at the seams with a hot-air gun. Our job is to install it, repair it and decide whether an aging TPO roof is still worth repairing. The first check is always the water path: trace it back from the stain, probe the seams along the way and look at the transitions where the sheet meets walls, curbs and drains.
A hot-air weld melts two sheets into one. A good weld leaves a steady bead of melt at the edge, and a probe drawn along it catches on nothing. Poor welds trace to a dirty sheet, a welder who rushed, damp material or uneven heating. After years of heat cycling, an older weld can also creep open at the end of a seam or at a T-junction, where three layers meet.
On an existing roof we probe each seam, mark every lift and choose between a small welded patch and a larger repair. Seams that cross a low spot are the first to fail, since ponded water, heat and dirt work on the same line, so a seam failure repair often goes together with a drainage correction. The photo record shows the probe results by location so the owner can see where the problems cluster. It also shows the seam length probed, so the owner knows how much of the roof the findings represent. A cluster at one wall or one run of roof usually points to movement or water in that area, which is a different repair from scattered single failures.
That window is a sustained period of roof-surface heat and solar exposure, in the weather service's words. A white TPO surface reflects much of that energy, but the sheet still goes through a daily swing from a cool night to a hot afternoon. Over years, UV and heat slowly change it: surface crazing appears, the sheet loses some flexibility and shrinks slightly at its edges, and flashings at walls and curbs begin to pull.
Thickness matters, because a thicker sheet has more material over the reinforcing scrim. A roof walk checks for exposed scrim, shrinkage at the walls, hardened areas near equipment and dirt that holds heat. A sheet like that might accept a silicone coating if the base is dry, or it might be at the close of its service life, in which case a moisture survey decides between a coating, a recover and a replacement.
Dolly's 50-to-70-mph gusts caused minor damage in populated Hidalgo County, Edinburg included, and the weather service's advice afterward was to inspect roof edges, flashings and rooftop equipment. TPO can be installed mechanically attached, fully adhered or ballasted, and each loads the roof differently. A mechanically attached sheet depends on the fastener pattern in the corner and perimeter zones. A fully adhered sheet depends on the bond and the substrate. A ballasted sheet depends on the weight and the edge restraint.
After a wind event we walk the perimeter first. We look for fluttering, lifted edges, displaced flashing and loose coping, because wind enters at the edge long before it reaches the field. Where an attachment pattern looks light for the exposure, we say so and price the stronger pattern as an option. A wind damage repair record ties the damage to the location on the roof.
Hanna's July 2020 visit left street flooding in Edinburg and a report of shingles blown off a roof. A roof drains only as well as its outlets, and a TPO sheet laid over a low spot will hold a pond that stains, collects algae and works on the weld. We look at the slope toward each drain, the drain bowl seal and the condition of scuppers and gutters.
Where the sheet ponds, a drain and scupper correction may involve a tapered insulation section, a new outlet or a reset drain. Algae on a white sheet shows where water stood and is easy to read from a ladder. The report marks each ponding area with its approximate depth after rain and states whether the fix belongs to the membrane or to the drainage.
Most TPO leaks start at a detail and not in the field. Inside corners, outside corners, pipe boots and curb bases are finished with formed or hand-cut pieces welded to the sheet. A cracked corner patch, a boot peeling off its pipe or a wall flashing that has dropped will let water in with nothing visible in the open roof.
We press along every vertical flashing for hollow spots, check the termination bar and sealant at the top edge and inspect each boot. Equipment bases fail often enough that we build curbs and supports with TPO-compatible details and reinforcement around each cut through the sheet. Condensate lines that drain onto the sheet wear a path through it over time, and the fix is a longer run or a pad.
Warehouses, medical buildings, schools, government offices and food or manufacturing plants all appear in the city's employment mix, and a low-slope roof on any of them is a candidate for a reflective single-ply, though the use of a building does not tell us what its roof is. Where a reroof changes insulation, the adopted 2018 energy code comes into the scope.
For owners in Edinburg and McAllen, we compare TPO with PVC and modified bitumen against the roof deck, the exposure, the exhaust on the roof and the budget before recommending one. The walk and the moisture readings set the repair boundary, and the written scope lists what is repaired, what is replaced and what is left for the next review.
Gauge changes the material over the scrim and the way the roof tolerates traffic and weathering. The building, the exposure and the manufacturer's warranty terms for each thickness settle which gauge fits.
A recover can work when the old roof tests dry and the deck is firm, with a slip sheet or cover board in between. A moisture scan and a few cuts settle that before material is ordered.
Most come from dirt, damp sheet, wind during welding or water standing on the seam. Probing every seam as it is made catches most weak welds before the crew moves on.
Not as well as PVC. Oils from exhaust can soften TPO, so roofs under restaurant fans often get another membrane or a protective pad.
The area is cleaned and the damage cut away, then a matching patch is welded down with overlap on every side and a probe run along its edge. Ponding gets its own correction so the patch is not undone by standing water.