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“Torch-on” and TPO are both used on low-slope roofs, but they solve the waterproofing problem in very different ways. Torch-on normally refers to an SBS-modified bitumen membrane installed using heat from a torch, while TPO is a thermoplastic single-ply membrane whose seams are hot-air welded.
Torch-on vs TPO roofing: which is better?
Neither system is automatically better. SBS/torch-on is often attractive where multi-ply redundancy, robust detailing and resistance to routine rooftop traffic matter. TPO is often attractive where a lighter-coloured single-ply membrane, hot-air welded seams and flame-free field seaming suit the building and installation constraints.
How are torch-on SBS and TPO roof systems different?
| Feature | Torch-on / SBS modified bitumen | TPO |
|---|---|---|
| Membrane format | Usually a multi-ply modified-bitumen assembly with base and cap sheets. | Thermoplastic single-ply sheet membrane. |
| Field seams | Heat-welded with torch application in torch-applied systems; other SBS application methods also exist. | Hot-air welded seams and details. |
| Surface | Often granulated cap sheet or other SBS surfacing. | Commonly white or light-coloured smooth membrane. |
| Typical strength | Multiple plies provide redundancy and a durable walking surface when correctly specified. | Fewer membrane layers; performance depends heavily on membrane thickness, weld quality and protection from puncture. |
RCABC publishes separate B.C. standards for SBS-modified bitumen systems and TPO membrane systems. Those standards treat both as complete roof assemblies with requirements for securement, insulation, drainage, penetrations and flashings—not just sheets laid over a deck.
Which system is more resistant to punctures and rooftop traffic?
For roofs with frequent HVAC service, ladders, tools and foot traffic, a robust multi-ply SBS assembly can be attractive because the cap sheet and lower ply provide layered protection. TPO can also perform well, but traffic routes should be controlled and walkway protection should be installed where service activity is concentrated.
Puncture resistance is not determined by membrane category alone. A thicker TPO over a suitable cover board may outperform a lightly protected membrane, while poorly installed SBS can still fail at flashings or drains.
How do installation constraints affect the choice?
Torch-applied SBS uses open flame during installation, so fire-prevention procedures, substrate conditions, combustible materials and site rules require careful management. Some buildings or owners may prefer a non-torch SBS application method or a thermoplastic system because of those constraints.
TPO field seams are welded with controlled hot air rather than open flame. Large membrane sheets can reduce the number of field seams, but wind, substrate condition and detail complexity still affect installation.
Does TPO make a building more energy efficient?
White TPO can reflect more solar energy than a dark roof surface and may reduce summertime roof-surface temperatures. The actual building-energy benefit depends on climate, insulation levels, HVAC loads, roof exposure and operating schedule.
A reflective membrane should not be chosen on colour alone. In B.C., drainage, wind resistance, condensation control and the overall thermal assembly still need to work together.
Which roof is easier to repair later?
Both systems are repairable when the membrane is identified correctly and remains compatible with the repair method. SBS repairs often involve compatible membrane patches and heat or adhesive application. TPO repairs rely on cleaning and hot-air welding compatible thermoplastic material to the existing membrane.
Age matters. As membranes weather, repairability can change. That is one reason regular commercial roof inspections and preventive maintenance are more useful than waiting for a leak.
Which roof system fits your building?
- Warehouse with limited rooftop traffic: TPO can be an efficient, practical system when properly detailed and secured.
- Building with frequent mechanical service: SBS may be attractive for multi-ply robustness, though protected TPO can also work.
- Occupied project with strict hot-work limitations: TPO or non-torch SBS options may simplify installation planning.
- Complex roof with many penetrations: installer experience and detail design may matter more than broad membrane category.
- Roof with poor drainage: fix drainage first; changing membrane type alone will not solve ponding.
Use Watershed Roofing's flat roofing and commercial roof replacement pages when the comparison moves from research to project scope.
Frequently asked questions
Is torch-on roofing the same as SBS roofing?
“Torch-on” usually refers to torch-applied modified-bitumen roofing, commonly SBS. SBS membranes can also be installed using other approved application methods, so the terms are related but not identical.
Is TPO a one-layer roof?
TPO is a single-ply waterproofing membrane, but the full roof assembly also includes the deck, air/vapour controls where required, insulation, cover boards, attachment, flashings and drainage.
Which system lasts longer?
There is too much overlap to choose a winner by membrane name alone. Installation quality, membrane specification, drainage, maintenance and rooftop traffic strongly influence service life.
Can TPO be installed over an old torch-on roof?
Sometimes a recover system is technically possible, but moisture, deck condition, attachment, code requirements and manufacturer requirements must be assessed first.
Which is better for a roof with lots of HVAC equipment?
Both can work. SBS often appeals because of multi-ply durability, while TPO can be protected with suitable cover boards and walkways. Detail quality and service-traffic planning are critical.
Technical basis: RCABC maintains current B.C. standards for both SBS-modified bitumen and TPO systems. Its SBS guidance describes common two-ply base-and-cap assemblies and torch application, while TPO is governed as a thermoplastic single-ply system using its own material and securement requirements.
Choose the assembly around the building.
Before choosing SBS or TPO, document the deck, insulation, drainage, rooftop traffic, penetrations and installation constraints so the comparison is technically meaningful.
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