What is a modified bitumen roof?
Modified bitumen sheets are asphalt blended with polymers, either SBS (rubber-like) or APP (plastic-like), over a reinforcing mat. Crews install two or more plies: a base sheet plus a granulated or coated cap sheet. Unlike single-ply roofs, the multiple layers mean one cut or puncture rarely becomes a leak right away.
A modified bitumen roof is an assembly. From the deck up it is usually: roof deck, insulation (tapered where water needs to drain), cover board, base ply, then cap sheet, with flashings at walls, curbs, pipes and drains, and metal at the roof edge.
Where it doesn’t fit, see when modified bitumen is the wrong choice below.
SBS vs APP: which modified bitumen fits?
SBS stays flexible across temperature swings and is installed with hot asphalt, cold adhesive, self-adhered sheets or a torch. APP is stiffer, resists UV well and is usually torch-applied. For occupied DFW buildings, many owners prefer cold-applied or self-adhered SBS to avoid open flame. The manufacturer’s system specification decides the method.
| SBS | APP | |
|---|---|---|
| Polymer | Rubber-like | Plastic-like |
| Flexibility | Stays flexible across temperature swings | Stiffer |
| Usual application | Hot asphalt, cold adhesive, self-adhered or torch | Usually torch-applied |
| Flame on site | Avoidable (cold-applied or self-adhered) | Usually needed |
Torch-down, cold-applied or self-adhered?
Torch application fuses the sheets with an open flame. It’s fast but requires trained crews and a fire watch. Cold-applied systems use adhesive, with no flame and some odor. Self-adhered sheets peel and stick, which suits occupied or flame-sensitive buildings. Each has trade-offs in speed, odor and weather limits, so the written scope should state the method.
| Method | How it works | Trade-offs |
|---|---|---|
| Torch-applied | Open flame melts the back of the sheet to fuse it | Fast; needs trained crews and a fire watch |
| Cold-applied | Sheets set in adhesive | No flame; some odor; cure time |
| Self-adhered | Peel-and-stick sheets | No flame or adhesive odor; weather limits at install |
We install modified bitumen by all three methods and pick the one that suits the building, the manufacturer’s system and what’s next to the roof. Roof Experts, LLC is Elevate (Holcim) and GenFlex certified.
What should a modified bitumen roof scope include?
A complete scope lists tear-off (including old gravel or built-up layers), deck repairs, insulation tapered to drains, cover board, the base and cap plies (SBS or APP) and the application method. It also covers flashing at walls and curbs, edge metal, drains and walkway areas. Use it to compare bids layer for layer.
| Scope item | What it means |
|---|---|
| Tear-off | Remove existing layers, including old gravel or built-up (BUR) layers; decided by core samples |
| Deck repairs | Replace or reinforce damaged deck areas where found |
| Insulation and taper | Type, thickness and taper plan to the drains |
| Cover board | Board under the plies that protects the insulation |
| Base and cap plies | Number of plies, SBS or APP, cap surface (granulated, coated or reflective) |
| Application method | Torch, cold-applied or self-adhered |
| Flashings | Walls, curbs, pipes, drains and scuppers |
| Edge metal, drains and walkway areas | Perimeter metal, drain rings, protected service paths |
| Closeout | Photos of the finished roof and your written workmanship warranty |
Ply count, cap sheet, insulation and cover board follow building code and the manufacturer’s specification for the system, and your written scope lists them.
Send us the address, and we’ll inspect the roof and give you a written scope. Get a commercial roof assessment or call (817) 754-9484.
Can an old built-up or tar-and-gravel roof be restored?
Sometimes. If the insulation is dry and the plies are sound, removing loose gravel and applying a compatible coating or a new cap sheet can extend service life. If moisture is widespread, or the roof has failed at many seams and flashings, replacement is the honest answer. Core samples decide whether restoring or replacing makes sense.
| Restore may work when… | Replace when… |
|---|---|
| Core samples show dry insulation | Moisture is widespread |
| Plies are sound and bonded | The roof has failed at many seams and flashings |
| Loose gravel can be removed cleanly | The deck is damaged or corroded |
| A compatible coating or cap sheet is approved for the surface | Drainage must be rebuilt with new taper |
Coating options for a sound roof are silicone roof coatings, or acrylic roof coatings where the roof drains well.
We use an infrared moisture scan to map wet insulation before recommending repair, recover or replacement.
Modified bitumen pros and trade-offs vs single-ply
Strengths: multi-ply redundancy, puncture and foot-traffic resistance, and familiarity to repair crews. Trade-offs: more weight and labor than single-ply, a dark or granulated surface unless you choose a reflective cap sheet or coating, and seams that rely on proper heat or adhesive bonding. It’s often the right fit for roofs with heavy rooftop equipment traffic.
| Modified bitumen | Single-ply (TPO, PVC, EPDM) | |
|---|---|---|
| Layers | Two or more plies | One membrane |
| Punctures and foot traffic | Strong | Depends on thickness and cover board |
| Weight and labor | More | Less |
| Surface | Dark or granulated unless a reflective cap sheet or coating is chosen | TPO and PVC white; EPDM usually black |
Where we’d recommend something else: TPO roofing when a white, reflective roof is the goal, EPDM roofing where the building already has rubber, or a coating for a sound older roof. To weigh the single-ply options against each other, compare TPO vs PVC vs EPDM side by side.
How long does a modified bitumen roof last, and what warranty comes with it?
Modified bitumen life depends on the number of plies, the cap sheet, drainage and maintenance, so we use the manufacturer’s literature for any year figures. Roof Experts, LLC gives a 2-year workmanship warranty on modified bitumen roofs, covering our labor. Manufacturer NDL warranties available. Your written scope says which options apply.
Most modified bitumen leaks start at laps, flashings, penetrations and edges. Repairs mean cleaning the area and bonding new plies or flashing with the same method as the roof. Inspections twice a year and after major hail or wind, with drains kept clear, catch those problems early. Our post on why commercial roof maintenance matters covers what a visit should include.
Our Commercial Roof Care Plan puts the roof on a schedule: inspections every spring and fall (quarterly visits on the top plan), drains and scuppers cleared, small repairs made on the spot, and a photo report with a Roof Condition Index score after every visit.
What does a modified bitumen project look like?
A modified bitumen project runs in five stages: we inspect the roof and take cores, give you a written scope with the SBS or APP system and application method, plan fire safety and odor control where needed, install ply by ply with daily dry-in, and close out with photos and warranty paperwork for your building’s records.
- Inspect. We walk the roof, take photos and core samples.
- Scope in writing. You get a written scope with the SBS or APP system, the application method and any options.
- Plan safety. A fire watch for any torch work, odor control for cold-applied work, and protected entrances.
- Install. Ply by ply, with the roof dried in at the end of each day.
- Close out. Photos of the finished roof, your written workmanship warranty and maintenance notes.
At closeout you get our workmanship warranty certificate, the manufacturer warranty certificate where a manufacturer warranty applies to your system, and lien waivers.
What affects the cost of a modified bitumen roof?
Each roof is priced after measurement and inspection, because cost depends on roof size, tear-off depth (including old gravel or built-up layers), deck repairs, insulation and taper, cover board, the number of plies and cap sheet, the application method, flashings and edge metal, access and fire-safety needs. We don’t publish prices.
- Roof area and shape (penetrations, curbs, parapets)
- Tear-off depth: old gravel, built-up layers, wet insulation found in cores
- Deck repairs
- Insulation, taper and cover board
- Number of plies, SBS or APP, and cap surface (granulated, coated or reflective)
- Application method (torch, cold-applied or self-adhered) and fire-watch needs
- Flashings, edge metal, drains and walkway areas
- Access, equipment and tenant scheduling
When is modified bitumen the wrong choice?
Modified bitumen is a poor fit where torch-down work is unsafe because of combustible materials near the roof, where the structure can’t carry added weight, or where wet insulation is already present. Cold-applied or self-adhered versions, a single-ply membrane or a coating may fit better. We say so in the written scope before you sign.
| Situation | Why modified bitumen is a poor fit | What to look at instead |
|---|---|---|
| Combustible materials near the roof | Torch work is unsafe | Cold-applied or self-adhered modified bitumen |
| Structure can’t carry added weight | Multi-ply roofs weigh more than single-ply | TPO roofing or another single-ply membrane |
| Wet insulation across large areas | New plies over trapped moisture fail early | Tear-off of the wet areas first, whichever system follows |
| Sound, mostly dry roof that is simply aging | Replacement may not be needed yet | Silicone roof coatings |
Roof Experts, LLC installs TPO, PVC, EPDM and modified bitumen roofs and applies silicone and acrylic coatings, so the system in your written scope is the one that fits the roof.
Why choose Roof Experts, LLC for modified bitumen roofing?
Roof Experts, LLC is an Arlington roofer serving Dallas–Fort Worth since 2017. We’re Elevate (Holcim) and GenFlex certified, insured and registered with the City of Arlington. We’re rated 4.9 on Google. Every proposal is written and itemized, and we take core samples before we recommend anything.
- Core samples before we recommend restoring or replacing.
- An itemized written scope you can compare layer for layer.
- Every application method, so the method fits your building rather than our crew’s habits. See all of our commercial roofing services.
Our office is at 4275 Little Rd #202, Arlington, TX 76016. To get started, get a commercial roof assessment or call (817) 754-9484.