For most California warehouses and offices, white TPO is the simpler choice: one heat-welded, reflective sheet that readily meets Title 24 cool roof rules. Modified bitumen earns its place on roofs with heavy foot traffic, lots of equipment or many penetrations, thanks to its multi-ply build. If you choose it, specify a CRRC-rated cool cap sheet.
If your old roof is torch down or “mod bit” and you are weighing a new mod bit roof against a switch to TPO, this guide covers how the two are built, how they handle heat, traffic and fire safety, and what California code says about recovering.
OneRoof Solution has installed and repaired commercial and industrial roofs across California since 2008 (CA License #930054), from offices in Visalia and Napa. We install and repair both systems: TPO roofing systems and new modified bitumen roofs, including torch-applied, hot-mopped, cold-applied and self-adhered mod bit. So we have no reason to push you toward one or the other. We work on commercial buildings only.
The two systems in plain terms
TPO (thermoplastic polyolefin) is a single-ply roof: one large sheet, usually white or tan, with seams welded together by hot air. The standard is ASTM D6878 (ASTM). Carlisle’s white and tan Sure-Weld TPO are ENERGY STAR qualified, and Carlisle describes them as California Title 24 compliant (Carlisle Sure-Weld TPO data sheet).
Modified bitumen (“mod bit”) is asphalt mixed with plastic or rubber-like polymers, made into rolls. It goes on in two or more layers: a base sheet and a cap sheet on top, often with a granule surface. NRCA’s Mark Graham counts more than 900 modified bitumen sheet products in the US market and 26 ASTM types and grades. NRCA recommends specifying them by their ASTM designation, including type and grade, so you compare like with like (NRCA, Professional Roofing, January 2019).
SBS vs APP modified bitumen
There are two main families:
- SBS (styrene butadiene styrene) is more rubber-like and stretchy. SBS sheets follow ASTM D6162, D6163 and D6164. GAF says SBS can be hot-mopped, cold-applied, heat-welded or self-adhered, depending on the product.
- APP (atactic polypropylene) is more plastic-like. APP sheets follow ASTM D6222 and D6223. GAF says APP is typically torch-applied.
(Standards: NRCA. Application methods: GAF.) Each product’s data sheet says how it may be installed.
Is torch down the same as modified bitumen?
Torch down is one way of installing modified bitumen: the crew heats the back of the sheet with a propane torch so it bonds. So “torch down vs TPO” is really “torch-applied mod bit vs TPO.”
Side-by-side comparison
| TPO | Modified bitumen | |
|---|---|---|
| Build | Single ply (one sheet) | Multi-ply (base sheet plus cap sheet) |
| Seams | Hot air welded into one piece | Laps torched, hot-mopped, cold-adhered or self-adhered, by product (GAF) |
| Surface and Title 24 fit | White and tan products are common. Check the product’s CRRC listing | Standard dark granules do not meet the low-slope minimum. Needs a CRRC-rated white cap sheet or coating |
| Foot traffic and punctures | Use walkway pads, a thicker sheet or fleece-back | Two or more plies, so a cut in the cap sheet is not an instant leak |
| Open flame on site | No. Seams are hot air welded | Only with torch-applied products. Cold, hot-mopped and self-adhered options exist |
| Repairs | Weld on a matching patch | Patch with compatible mod bit materials |
| Installed cost (national, 2026) | $6.50 to $9.50 per sq ft | $6.00 to $9.00 per sq ft |
| Standard | ASTM D6878 | SBS: ASTM D6162, D6163, D6164. APP: ASTM D6222, D6223 |
Cost row: Commercial Roof Guide, March 2026. Those figures include insulation and standard flashings but exclude tear-off and permits. Another 2026 guide lists TPO at $4.50 to $7.50 and modified bitumen at $5.00 to $8.50 (Paletz Roofing, September 2026). In both, the two land in a similar range, so your building decides the price more than the label. These are national figures, not OneRoof prices. We quote every roof after we see it.
Heat and California’s cool roof rules
California’s 2025 Energy Code has cool roof rules for nonresidential reroofs. They apply when more than 50% of the roof, or more than 2,000 sq ft, whichever is less, is replaced, recovered or recoated (California Energy Commission, 2025 Nonresidential Cool Roofs).
For low-slope roofs, the product must have a 3-year aged solar reflectance of at least 0.63 and a thermal emittance of at least 0.75, or a Solar Reflectance Index (SRI) of at least 75, with some listed exceptions. Products must be rated by the Cool Roof Rating Council.
- White TPO often meets this. Check the exact product in the CRRC Rated Products Directory.
- Modified bitumen with a standard dark granule surface does not. You would need a white reflective cap sheet or a coating that is CRRC rated and meets the aged values. Ask the bidder to name the exact cap sheet, then look it up.
On a hot Central Valley roof, this often tips the choice toward white TPO.
Foot traffic, equipment and punctures
Mod bit has two or more layers, so if a dropped tool cuts the cap sheet, there is still a sheet below. That suits roofs packed with equipment or walked by service crews every week.
TPO can handle traffic too, with the right build:
- Walkway pads along the paths service crews use. GAF notes that its warranties do not cover traffic damage except where GAF walkways are installed (GAF EverGuard fleece-back data sheet), so pads protect the warranty as well as the roof.
- A thicker sheet. Commercial Roof Guide says 80 mil TPO resists punctures better than 60 mil (Commercial Roof Guide, 2026).
- Fleece-back TPO over a cover board. Carlisle says its 115 mil FleeceBACK TPO has 33% greater puncture resistance than 60 mil TPO (Carlisle FleeceBACK TPO data sheet), and GAF calls its 100, 115 and 135 mil fleece-back membranes especially suitable for high-traffic roofs (GAF).
Our recommendation. For a roof crowded with equipment or walked every week, we recommend 115 or 135 mil fleece-back TPO adhered over a cover board, with walkway pads on every service path. That is the build we used at a Richmond industrial facility, where we installed 115 mil FleeceBACK TPO over a fully adhered DensDeck Prime cover board, and at a Los Altos office, where we used 135 mil fleece-back TPO. For a big, simple warehouse with light traffic, 60 mil white TPO is a sound standard, with 80 mil worth pricing for extra toughness. If you prefer a multi-ply roof, mod bit with a CRRC-rated white cap sheet is also a strong choice.
Torch-applied roofing on an occupied California building
Torch-applied mod bit is a proven system, and our crews install it. Because it uses an open flame, it has to be done with care. The 2025 California Fire Code, Section 3305.10, says roofing work that uses heat-producing systems or other ignition sources must follow the code’s hot work chapter, and at least one multipurpose fire extinguisher must be kept on the roof being worked on (2025 California Fire Code, Section 3305, GoCodeBook).
On every heat job, we follow safe, permitted hot work practices: trained crews, any permits the local fire authority requires, fire extinguishers on the roof, a fire watch, and a careful check of the work area before we leave. We plan the work around your building and talk it through with you, and with your insurer if they ask.
Some buildings are better suited to a flame-free system, such as food plants, cold storage buildings with foam insulation, and buildings with combustible decks or details. Flame-free options include:
- heat-welded TPO or PVC (hot air, no open flame), and
- cold-applied or self-adhered modified bitumen.
Replacing an old mod bit or built-up roof
You may not need to tear off the old roof. The 2025 California Building Code, Section 1512.3, allows a new roof over an existing modified bitumen or built-up roof in many cases. A recover is not allowed if:
- the existing roof is water-soaked, or too worn out to be a good base, or
- the roof already has two or more layers.
(2025 California Building Code, Section 1512.3, UpCodes)
The new membrane maker must also approve the recover, often with a cover board or separator sheet, and a recover that crosses the Title 24 trigger must meet the cool roof rules above.
What a switch looks like. At the American Inc. office and shop in Visalia, we tore off an old gravel-surfaced built-up roof and installed a new single-ply roof and acrylic coating system across 100,000 sq ft. The old roof was past its service life and its problems went beyond what patching could fix, so a full tear-off was the responsible choice. It gave the owner a dry, sound base and a new roof built to last.
Tear-off changes the price a lot. See commercial roof replacement cost per square foot for how.
Seams, leaks and future repairs
TPO seams are welded with hot air into one piece. Mod bit laps are joined by torch, hot asphalt, cold adhesive or a self-sealing strip. Both can be repaired with matching materials. Whether a future leak is easy to trace also depends on the deck, so see our guide to commercial roof leak detection.
Lifespan and warranty: what you can count on
Blog lifespans are rarely sourced. A manufacturer’s written warranty is a better planning number. Terms depend on the maker, system, thickness and, for mod bit, the number of plies, so get the exact term in writing.
We are certified or authorized applicators for Carlisle, GAF, Duro-Last, Versico, Henry, CertainTeed and American Standard Coatings, so manufacturer system warranties are available on qualifying roofs. Ask us about warranty options for your building.
Warranties depend on regular care. Carlisle’s Golden Seal warranty, for example, can be voided by unapproved repairs or rooftop additions, or if the owner does not take reasonable care of the roof (Carlisle warranty PDF). Our Rainshield Roof Care Program helps you keep your warranty valid with scheduled inspections.
Quick picker: which roof for which building
- Big, simple warehouse roof in Central Valley sun, light foot traffic: usually 60 mil white TPO.
- Roof packed with equipment and weekly service traffic: 115 or 135 mil fleece-back TPO over a cover board with walkway pads, or mod bit with a CRRC-rated cool cap sheet.
- Existing mod bit in fair shape, one layer, dry: a recover may be allowed. Check Building Code Section 1512.3 and the Title 24 trigger.
- Wet roof, or two or more layers already: tear-off.
- Food plant, kitchen exhaust or oils on the roof: compare PVC too. See TPO vs PVC vs EPDM.
- Foam insulation, combustible deck or no open flame allowed: choose a flame-free system.
FAQ
Is TPO better than modified bitumen?
For most California warehouses and offices, white TPO is the simpler fit. It is one welded, reflective sheet that often meets Title 24 cool roof rules. Modified bitumen is a strong choice for roofs with heavy foot traffic and lots of equipment, as long as it has a CRRC-rated cool surface.
What is the difference between SBS and APP modified bitumen?
SBS is rubber-like and can be installed several ways: hot asphalt, cold adhesive, torch or self-adhered, depending on the product. APP is plastic-like and is typically torch applied. They follow different ASTM standards, so compare products with the same ASTM type and grade.
Is torch down roofing good for a commercial building?
Yes, when it is installed by a trained crew following safe hot work practices. California Fire Code Section 3305.10 requires heat-based roofing to follow the hot work rules, with a fire extinguisher on the roof. On food plants, cold storage with foam insulation or combustible decks, a flame-free system is often the better fit.
Can you put TPO over modified bitumen?
Often, yes, if the old roof is dry, sound and only one layer, and the TPO maker approves it, usually with a cover board. California Building Code Section 1512.3 does not allow a recover over a water-soaked roof or a roof that already has two or more layers.
Does modified bitumen meet California cool roof requirements?
Only with a cool surface. A low-slope reroof needs an aged solar reflectance of 0.63 and emittance of 0.75, or an SRI of 75, with some exceptions. Standard dark granules do not meet this. Look up the exact white cap sheet or coating in the CRRC directory.
Which is better for a flat roof with a lot of HVAC equipment?
Both can work. Mod bit’s multi-ply build handles punctures well. Fleece-back TPO (115 or 135 mil) over a cover board, with walkway pads at every service path, is also a solid choice and is easier to make cool roof compliant. Have your roofer walk the roof and see where crews actually step.
Weighing mod bit against TPO?
Book a roof assessment. We will check your roof’s layers, moisture and traffic, and tell you plainly whether to repair, recover or replace, and which system fits.
Have bids naming different systems? Send them to us and we will point out what is missing.
Call (855) 762-7663, or (707) 440-2351 for our Napa office, or email sales@1roofsolution.com. For a roof emergency, call our 24/7 line at (559) 697-6252.