TPO, Torch-Down or Modified Bitumen: Which Flat Roof Should You Choose?
Three names, two systems: torch-down is one way of installing modified bitumen. Here is how they compare with TPO on a Valley flat roof.
For a small flat section over a garage or addition, two-ply torch-down modified bitumen is the proven, economical choice. For larger roofs and commercial buildings, heat-welded white TPO wins. Planning figures for 2026: torch-down $4.50–$8 per sq ft and TPO $5–$9 per sq ft installed. TPO's white surface meets the low-slope cool-roof numbers without a coating; a torch-down roof needs a reflective cap sheet or coating to do the same.
Modified bitumen is the material; torch-down is the most common way it is installed in the Valley, with the sheets heat-fused in place. Self-adhered modified bitumen avoids the open flame and is used where a torch is not safe.
Flat roof systems at a glance
| TPO single-ply | Torch-down modified bitumen | Self-adhered modified bitumen | |
|---|---|---|---|
| Planning cost (2026, installed) | $5–$9 per sq ft | $4.50–$8 per sq ft | Quoted per roof |
| Seams | Heat-welded | Torch-fused laps | Pressure-sealed laps |
| Reflectance | White, meets low-slope cool-roof numbers | Needs a reflective cap sheet or coating | Needs a reflective cap sheet or coating |
| Typical life in the Valley | 20–30 years | 15–25 years | Similar to torch-down |
| Best use | Larger roofs, commercial, whole low-slope homes | Garage conversions, additions, small sections | Where an open flame is not safe |
Is torch-down the same as modified bitumen?
Torch-down is modified bitumen installed with a torch. Modified bitumen is asphalt modified with rubber or plastic polymers, made into rolls with a reinforcing mat; the roofer heats the back of each roll and rolls it onto a base sheet so the layers fuse. A two-ply system, a base sheet plus a granulated or reflective cap sheet, is the standard on Valley garage conversions and additions. Self-adhered sheets do the same job without a flame.
Why do larger roofs use TPO?
TPO is a single-ply thermoplastic membrane in wide rolls, so a large roof has far fewer seams, and each seam is hot-air welded into one continuous sheet that is stronger than the field. Its white surface reflects most of the sun, which matters on a commercial roof with rooftop equipment and on a mid-century house whose whole roof is low-slope.
Do flat roofs have to be cool roofs?
When more than half of a home's low-slope roof is replaced, recovered or re-coated, the 2025 Energy Code sets 0.63 aged solar reflectance, 0.75 thermal emittance or SRI 75 in Climate Zone 9. Nonresidential roofs meet the same numbers when more than 50% of the roof or 2,000 sq ft, whichever is less, is altered. White TPO meets them; a torch-down roof does it with a rated reflective cap sheet or coating.
When is a coating better than either?
When the existing membrane is dry and still bonded to the deck. A silicone coating over a sound roof plans at $2–$4 per sq ft, a fraction of a replacement, after the seams, drains and flashing are repaired. Over a wet or blistered roof it only seals the problem in. See roof coating.
When does torch-down win?
- A small flat section over a garage conversion, patio enclosure or addition.
- A roof with many penetrations and transitions to a pitched roof, where crews are used to detailing it.
- A tight budget on a residential section.
When does TPO win?
- Larger residential flats and commercial roofs, where fewer seams matter.
- Any roof where the cool-roof requirement applies and you want to meet it without a coating.
- Roofs with rooftop HVAC, where a reflective surface lowers heat at the equipment.
What we recommend
Fix the drainage first on any flat roof, because ponding shortens every membrane. Then choose by size: torch-down for the small residential section, TPO for the large roof or the commercial building, and a coating only when a moisture check shows the existing roof is sound.
Where does this come up in the Valley?
The typical roofing jobs in the neighborhoods where this choice comes up most:
- Sherman Oaks: Shingle tear-off and re-roof on the 1950s ranches, flat-section leak repairs where a low-slope addition meets the main roof, and tile underlayment replacement on the south-of-Ventura homes.
- Studio City: Re-roofs on the Colfax Meadows ranches, canyon-house leak repairs at skylights and dormers, and Class A replacements in Fryman and Laurel Canyon.
- Van Nuys: Two-layer tear-offs on the 1950s tracts, flat-roof repairs over converted garages, and full shingle replacements before a sale.
- Encino: Tile underlayment replacement on the 1980s–90s tile roofs, large shingle re-roofs on the estate lots, and hillside repairs where tile meets a flat section.
- Valley Village: Bungalow re-roofs with new plywood decking, flashing repairs at older chimneys, and flat-section repairs where additions tie into the main roof.
- Valley Glen: Multi-layer tear-offs on the 1940s–50s ranches, torch-down repairs over converted garages, and full re-roofs timed before the winter rains.
Related pages
- Flat roof repair and replacement
- Flat roof repair in Sherman Oaks
- Roof coating
- Commercial roofing
- Roofing in Reseda
- Roofing FAQ: materials
Sources
Questions We
Hear About This
In Valley conditions TPO typically runs 20 to 30 years and torch-down 15 to 25. Installation quality, drainage and maintenance matter more than the label on the roll.
Planning figures for 2026: TPO $5–$9 per sq ft and torch-down $4.50–$8 per sq ft installed. On small residential sections the totals are close; on large roofs TPO's fewer seams and built-in reflectance often make it the better value.
Yes, with a reflective cap sheet or a rated coating. A dark granulated cap generally does not reach the low-slope reflectance numbers on its own.
Torch-down is installed with an open flame, so crews keep fire extinguishers on the roof and use self-adhered sheets near wood edges and other spots where a torch is not safe.
Water that stands. Ponding at a clogged scupper or a low spot works into seams and edges, so drainage is fixed before or during any flat-roof repair or replacement.
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