Roof Repair
Leak diagnostics and repairs on occupied flat roofs — traced to the detail that failed, scoped in writing.
Learn moreCommercial Roofing
Where single-ply is one sheet doing all the work, a modified bitumen roof is built from layers: a base sheet fastened or adhered to the substrate, one or more interply sheets, and a cap sheet on top, each of them asphalt reinforced with a polyester or fiberglass mat and modified with a polymer to stay flexible. Redundancy is the point. A puncture in the cap sheet has more material under it before water reaches the insulation, and the thick, granulated surface stands up to technicians walking to rooftop units in a way a thin thermoplastic sheet does not.
That toughness is why we see modified bitumen on hotel roofs, hospitals, schools and any building whose mechanical systems get serviced constantly. It is also the system most likely to have been repaired badly, because anyone with a bucket of mastic can smear a patch on it. Those patches hold for a season, then the asphalt under them keeps weathering. Done properly, a mod-bit repair is a welded or adhered cap-sheet patch, and a well-built mod-bit roof is one of the most repairable systems there is.
SBS or APP, and how it goes down
- SBS (styrene-butadiene-styrene)Rubber-modified; flexible and elastic, handles movement well; cold-applied, self-adhered or torched
- APP (atactic polypropylene)Plastic-modified; stiffer, more UV-tolerant surface; torch-applied
- Torch-appliedFast, strong bond; open flame means a fire watch and no torching near combustible details
- Cold-appliedAdhesive-bonded; no flame, slower cure, good for occupied buildings and sensitive sites
- Self-adheredPeel-and-stick; no flame or fumes; substrate prep and temperature matter
- Granulated cap sheetMineral surface protects the asphalt from UV; white granules add reflectivity
On an occupied building in Orlando we lean toward cold-applied or self-adhered SBS, both because it removes open flame from a roof full of HVAC intakes and because SBS handles the daily heat cycling here better than a stiffer sheet does.
Where modified bitumen fails in Central Florida
Sun is the enemy. Once the granules wear off the cap sheet, the asphalt beneath is exposed to UV and begins to dry out, checker and crack in a pattern that looks like alligator hide. That surface then holds water in the cracks, which accelerates it. Blisters form where moisture or air trapped between plies expands in the afternoon heat, and once a blister breaks open the roof is taking on water. Laps that were not fully bonded creep open with thermal movement; on a torch job they are often the places the roofer was rushing near a detail. Flashings at parapets and curbs fail when the base flashing was not run high enough or the metal counterflashing was skipped, and ponding water finds all of these faster than a roof that drains.
Each of those is visible to someone walking the roof, which is why an annual look catches most of them while they are still small patches.
Repairs, and why the material matters
The right patch for a mod-bit roof is a compatible cap sheet, torched or adhered over a primed, cleaned area with the granules embedded back in at the edge, so it becomes part of the membrane. The wrong patch is a trowel of roof cement over a wet surface, which is what most of the failed repairs we find turn out to be. Blisters are cut open, dried, and re-laid with new plies. Open laps are re-bonded and reinforced. Alligatoring across a whole roof is not a repair; it is a surface that has run out of protection, which leads to the next question.
If water is coming in right now, the emergency leak page covers the dry-in; for a roof that has leaked on and off, the commercial repair page explains the diagnostic.
When a coating over mod-bit makes sense
A modified bitumen roof that is dry underneath, with plies still bonded and only the cap-sheet surface weathered, is a strong candidate for a fluid-applied coating. The granulated surface takes an acrylic or silicone system well after cleaning and priming, seams and flashings are reinforced with fabric first, and the result is a reflective surface that puts the UV protection back over asphalt that still has life in it. That is a fraction of the disruption of a tear-off and can often be funded from an operating budget rather than a capital one.
It is the wrong choice when a moisture survey finds wet insulation, when the plies have delaminated, or when the deck below has started to fail. Sealing a wet roof in makes the eventual replacement worse. Our roof coatings page goes through how the eligibility decision gets made.
Foot-traffic roofs and rooftop equipment
Modified bitumen earns its place on roofs that get walked: hotels with cooling towers and exhaust, medical buildings with technicians on the roof weekly, schools with rooftop units above every wing. We still add walk pads along the service routes, because even a granulated cap sheet wears where boots go the same way every day, and we flash equipment curbs with a two-piece base and counterflashing so a unit can be serviced without disturbing the roof. Where a building is fully occupied and flame is not acceptable, cold-applied SBS is the answer, and we schedule the fume-heavy phases outside occupied hours where the site allows it. Call (407) 871-6159 if you have a mod-bit roof anywhere from Altamonte Springs to Kissimmee that has been patched more than once and you want a straight read on it.
More commercial roofing services
TPO Roofing
Heat-welded, reflective single-ply for low-slope roofs — and a straight answer on when TPO is the wrong pick.
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Roof Replacement
The whole decision, laid out: when a flat roof is done, tear-off vs re-cover, phasing, staging, permits, close-out.
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Metal Roofing
Standing seam and panel systems for churches, schools and commercial buildings — retrofit or new, engineered for wind.
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Roof Coatings
Fluid-applied silicone or acrylic over a sound membrane — a restoration, not a replacement, and only when the survey says so.
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PVC Roofing
Welded single-ply that shrugs off grease and chemicals — the right call for kitchens and processing roofs.
Learn moreCommon questions
Related, not the same. A built-up roof is layers of felt mopped in hot asphalt and topped with gravel, the tar-and-gravel roof on older Orlando buildings. Modified bitumen uses factory-made sheets with the asphalt already applied and polymer-modified for flexibility, so the plies are consistent and the installation is cleaner. Many mod-bit roofs are installed over an old built-up roof as a re-cover.
For an occupied building with rooftop air intakes, cold-applied or self-adhered SBS removes the open flame and the fire watch, and the bond is fully adequate. Torch-applied APP is fast and strong and suits an unoccupied building or new construction where the details allow it. The substrate, the weather window and what is on the roof decide; we spell out which and why in the scope.
Moisture or air got trapped between plies, or between the base sheet and the substrate, and it expands every afternoon in the sun. Sometimes the plies were laid over a damp surface; sometimes a small leak wet the insulation from below. Small closed blisters can be monitored. Blisters that have opened, or that sit in a walkway, get cut out and re-plied before they become leaks.
It depends how far it has gone. Surface cracking with the plies still bonded and dry insulation underneath is the classic case for cleaning, priming and a reflective coating that restores the UV protection. Cracking that has gone through the cap sheet, with wet insulation under it, is beyond coating and becomes a section replacement or a re-cover. A moisture survey is how we tell the two apart.
Yes. Cap sheets are available with white or light-colored granules, and some carry a factory-applied reflective surface, which gives a mod-bit roof a reflectivity close to a white single-ply. On an Orlando building with conditioned space under the roof that reduces cooling load and keeps the asphalt cooler, which slows its aging. We specify a reflective cap sheet unless there is a reason not to.
Long enough to be worth maintaining well, and materially longer when it is. The variables are UV exposure of the cap sheet, drainage, how much traffic it takes and whether small failures were repaired properly. A roof kept clear at the drains, coated when the granules wear, and repaired with the right material outlasts an identical roof that was patched with mastic and left to pond. We will not quote a number of years without seeing it.