Roofing materials
TPO roofing for Philadelphia flat roofs
TPO is the bright white membrane showing up on more and more Philly roofs. Its seams are melted together instead of glued, and it bounces summer sun back off the house. It's a strong choice, but more than most roofs, how well it lasts depends on who installs it.
The material
What TPO is
TPO (thermoplastic polyolefin) is a single-ply roofing membrane with a reinforcing fabric inside. "Thermoplastic" is the important part: it softens with heat and hardens again as it cools. That lets a roofer join two sheets by melting their edges together with a hot-air welder, so the seam becomes one continuous piece of plastic.
It's made in white and a few light colors, in common thicknesses of 45, 60 and 80 mil. On rowhomes it's either glued down over insulation or fastened through the insulation into the roof boards, with the fasteners hidden under the overlapping seams.
A well-installed TPO roof generally lasts 20 to 30 years. Thicker sheets and good maintenance push toward the longer end.
Is TPO worth a look?
It's often a good fit when:
- Top-floor bedrooms are hot all summer
- You're replacing a black tar or rubber roof anyway
- The roof is wide or has many seams, like a mixed-use building
- There's equipment on the roof that needs clean, strong flashing
- You can find an installer with a solid TPO track record
What it does well
Why Philly homeowners choose TPO
Cooler top floors
A dark roof in a Philadelphia summer gets far hotter than the air. A white TPO surface reflects much of that sun, so less heat reaches the ceiling below and the AC works less hard.
Welded seams
A properly welded seam doesn't rely on glue or tape. Done right, it's as watertight as the sheet itself, which is a real advantage on roofs that need several pieces.
Clean flashing details
Walls, curbs and pipes are flashed with TPO pieces welded to the roof, and edges use metal coated in TPO so the membrane can be welded right to it.
Where TPO is weaker
- It's stiffer than rubber, so tight corners and cold-weather installs take more skill
- Aged, weathered TPO is harder to weld new patches to, so later repairs need careful cleaning
- Dirt and grime build up and dull the white surface over time
- Early formulations from years past had problems; quality varies by manufacturer and product line
The part most people miss
Why the installer matters more than the brand
Welding TPO is a skill. The welder's heat and speed have to suit the day's temperature and the sheet's thickness. Too cold and the seam only looks bonded; too hot and the membrane scorches. A careful crew runs a test weld before starting, pulls it apart to check it, then checks every finished seam with a probe to find any gaps.
Most TPO problems trace back to those seams and to the flashing at walls and corners, not to the material. On a rowhome, that means the party walls, the hatch, any skylight and the tie-in to the neighbors' roofs.
Questions to ask a TPO installer: Do you run a test weld each day? Do you probe every seam? How will you flash the party walls and the hatch? How many TPO roofs have you installed on rowhomes?
The work
What installing a TPO roof involves
Strip & prepare
The old roof comes off, damaged boards are replaced, and insulation board goes down, tapered where water has been sitting.
Lay & secure
Sheets are rolled out and either glued down or fastened through the insulation, with fasteners hidden under the seam overlaps.
Weld & test
Overlaps are hot-air welded after a test weld, then every seam is checked with a probe.
Flash & finish
Walls, curbs and pipes get welded TPO flashing, and the edges get TPO-coated metal.
Planning your job
What affects the price
On a TPO roof, the scope comes down to:
- Tear-off. How many old roofs come off, and the condition of the boards beneath.
- Membrane thickness. Thicker sheets add durability and material.
- Glued or fastened. The attachment method changes labor and materials.
- Insulation and tapering. Extra insulation or tapered board to stop ponding.
- Detail work. Every wall, curb, pipe, hatch and condenser stand needs welded flashing.
- Getting it up there. Rolls, insulation and the welder all have to reach the roof.
Not sure your roof is ready for replacement? Try the Roof Problem Checker.
Related pages
- EPDM rubber roofs: the main alternative for rowhomes
- Flat roof materials compared: TPO, EPDM and modified bitumen side by side
- Flat roof replacement: the full replacement process
- Silver coat roof replacement: trading a tar roof for a white one
- Center City flat roof repair: larger and mixed-use roofs
TPO roofing questions
Does a white TPO roof really make the house cooler?
It usually makes the top floor noticeably more comfortable, because the roof surface stays much cooler in direct sun. How much you notice depends on how well the roof is insulated and how the top floor is ventilated.
Is TPO a problem in Philadelphia winters?
No. Once it's installed, TPO handles freezing temperatures fine. Cold weather mainly affects installation: welding settings have to be adjusted, and some installers prefer milder days for detail work.
How can I tell if my TPO roof was installed well?
Look at the seams: they should be flat and continuous, without wrinkles, gaps or scorched brown edges. Flashing at walls should run smoothly up and be finished at the top. If you're not sure, a roofer can probe the seams and check the details.
Will the roof stay bright white?
Not forever. City grime, leaves and dust dull it over time, which reduces how much heat it reflects. Gently cleaning it every few years helps. Avoid pressure washers set too high, which can damage the surface.
Can an old TPO roof be repaired?
Yes, but weathered TPO has to be cleaned and prepared carefully before a patch will weld to it. A roofer will check whether the existing membrane still takes a weld before recommending a repair over a replacement.
Have a different question about TPO? Call and ask a local roofer.
(215) 702-6130