TPO and Single Ply Roofing for Flat and Low-Slope Roofs in Florida

TPO stands for thermoplastic polyolefin. It is a single ply roofing membrane, a sheet of reinforced plastic that comes in wide rolls, usually white, in thicknesses measured in mils. It replaced tar-and-gravel and much of the modified bitumen on small commercial buildings because it goes down faster, weighs less, and reflects the sun.

It belongs on any roof too flat to shed water by pitch alone. That includes the low-slope deck over a strip of shops, the flat wing on a church, the warehouse with internal drains, and on a house, the addition with a quarter inch of fall per foot, the porch roof with a wall on the high side and the carport. Anything below about a 2:12 pitch is membrane territory. Above that, we talk about metal roofing or shingles.

The reason TPO holds up is the seam. Rolls of membrane are laid out with an overlap, and a hot-air welder runs down the overlap, melting the two sheets into each other. When it cools, the seam is not glued or taped; it is one piece of plastic. Flashings at walls, curbs and pipes are welded the same way, so every joint on the roof is fused instead of relying on a bead of sealant that will dry out in three Florida summers.

That is also why the installer's skill matters more than the brand of membrane. Welder temperature, speed and pressure change with the weather, and a cold seam looks fine and peels open in a year. Juan checks welds as they cool, and the crew probes every seam before the roof is called finished.

There are two ways to hold a single ply roof on a building.

Mechanically fastened: the membrane is laid over the insulation, and screws with plates are driven through the sheet into the deck along the seam line, where the next sheet's overlap will cover them. It is the faster and less expensive method, it works well over a wood or steel deck, and it is common on small commercial roofs.

Fully adhered: the membrane is glued to the insulation or a cover board across its whole surface. No fasteners through the sheet, no flutter, a flatter finished look, and better wind uplift performance on a roof with a lot of exposure. It costs more in labor and adhesive and needs dry weather to set, which in a north Florida summer means an early start.

Juan tells you which one the roof should get and why.

Under the membrane is rigid insulation, usually polyiso board, fastened to the deck. It keeps the building cooler and gives the membrane a smooth, uniform surface.

Then there is the slope. A flat roof is never truly flat, and the low spots hold water. A puddle that stays more than a couple of days after a rain is ponding, and ponding is what kills flat roofs: it stresses the seams, grows algae, breeds mosquitoes, and adds weight to the deck. Tapered insulation fixes it. The boards are cut in wedges that build a slope toward the drains. On a re-roof we map where the water sat, and the tapered layout is designed to move it.

Membrane in the middle of the roof almost never leaks. The edges and the holes do. On every TPO job the details get more of Juan's time than the field.

Internal drains get new clamping rings and a strainer, with the membrane welded to a drain flashing. Scuppers, the openings through a parapet that let water off the roof, are lined and welded in. Overflow scuppers go in where the code wants a second way out if a drain clogs with pine needles, which in Putnam County it will.

Parapet walls and curbs get membrane run up the wall and terminated under a metal cap or a termination bar. HVAC curbs, pipes and vents get pre-formed boots or field-wrapped flashing, welded.

Any one of these done quickly is a leak in the first hard rain. The roof leak repair page describes how we chase water on a flat roof when someone else's edge detail fails.

A black flat roof in August is hot enough to soften the asphalt in it. A white TPO membrane reflects most of the sunlight that hits it, so the roof surface runs far cooler, the building under it needs less air conditioning, and the membrane itself is not being cooked every afternoon. We wrote about the same principle for metal in which metal roof color is the most energy efficient in Florida.

If the old roof is dry, the deck is sound and there is only one existing layer, a new TPO roof can sometimes go over it with a separation layer or new insulation. The Florida Building Code limits how many roof layers a building can carry, and wet insulation has to come out, so the decision starts with a moisture check. Juan probes the old roof, cuts a test square where it looks suspicious, and if the insulation is saturated, it is a tear-off. A roof replacement on a flat roof is a bigger job than a re-cover, and it is the only honest one when the roof underneath is wet.

TPO can be walked on, and a service tech will walk on it to reach the air conditioner. Walkway pads welded to the membrane along the path to the HVAC units take that traffic instead of the roof. Beyond that, a flat roof asks for a little attention twice a year: clear the drains and scuppers, sweep off the pine needles and oak leaves, look at the seams and the flashings, check the sealant at the termination bars. Our roof inspections include flat roofs.

We install TPO across our service area, on commercial buildings in Jacksonville, Daytona Beach and Palatka, and on the flat additions and porches of houses across Putnam County. For a house, financing through Regions Bank applies to a flat roof the same way it applies to any other roof we install.