TPO Roofing

Both are asphalt reinforced with polymer and a fiberglass or polyester mat. The polymer is the difference.

• SBS (styrene-butadiene-styrene) — rubberized modified bitumen. Flexible and elastic, it handles building movement and deep-cold thermal cycling well, which is why it is the more common specification across Missouri, Kansas, Illinois and Indiana. Installed with hot asphalt, cold adhesive or as a self-adhered peel-and-stick sheet.
• APP (atactic polypropylene) — plasticized modified bitumen, more rigid and more heat tolerant, and generally torch-applied. Strong UV performance; less elastic in extreme cold.

Four application methods: torch-applied (flame-melted to bond, fast and durable, and requires a disciplined crew and fire watch), hot asphalt mopped (traditional, effective, and odorous), cold adhesive (no open flame, good near occupied buildings), and self-adhered (peel-and-stick, the safest option on schools, hospitals and occupied sensitive buildings).

Assembly: deck, insulation (usually polyiso, tapered where slope needs correcting), base sheet, one or more interply sheets, then a granulated or smooth cap sheet. Cap sheets come granulated for UV protection and walkability, or smooth for coating.

• Roofs with heavy foot traffic — restaurants, hospitals, schools, buildings whose equipment gets serviced weekly. A granulated cap sheet takes boots better than any single-ply membrane.
• Roofs with many penetrations and complex details — pipes, curbs, drains, parapets, odd geometry. Flashing details in modified bitumen are robust and time-tested.
• Buildings where redundancy matters — two or three plies mean one puncture is not one leak. On a building with inventory, records or sensitive equipment underneath, that is real risk reduction.
• Small, cut-up roofs where single-ply seam runs would be awkward.
• Roofs that will be coated later — a smooth cap sheet takes a reflective coating well, giving a long two-stage life.

Where it is not the answer: very large open roofs where a single-ply system is faster and cheaper per square (see TPO), buildings where reflectivity is a priority without a coating, and heavy grease exposure, where PVC belongs.

A properly built two- or three-ply modified bitumen roof generally delivers 20 to 30 years, and a well-maintained system that gets coated at the right moment can run longer. Ply count matters: three plies outlive two, and the difference shows up in year eighteen, not year three.

The Midwest failure driver is thermal cycling plus UV. Granules protect the asphalt from ultraviolet light, and as granules are lost — scoured by hail, ground off by foot traffic, washed into drains — the asphalt below oxidizes, hardens and eventually cracks. That is why granule loss in a gutter or at a downspout outlet is a real diagnostic, not a cosmetic one, and why a reflective coating applied before cracking begins is one of the highest-return maintenance decisions available on this system.

Modified bitumen shows hail more honestly than single-ply does, which helps a claim: impact produces visible bruising, granule displacement and, at the extreme, fractures through the cap sheet. A test square documents density per 100 square feet in a way an adjuster can follow, and corroborating damage to soft metals, vents and equipment strengthens the file.

Wind failures concentrate at perimeters and corners, as on every low-slope roof: lifted cap sheet at the edge, failed termination bars, displaced coping and edge metal. On torch and hot-applied systems, blisters and voids from moisture trapped at install become uplift weak points years later.

Commercial policies often carry percentage or per-building deductibles and sometimes cosmetic exclusions — read yours before a storm. We photograph, document and meet your adjuster at the building. See storm damage and roof insurance claims.

• Blisters — voids between plies from trapped moisture or poor bonding at install. Not every blister needs cutting; one that has broken open does.
• Granule loss exposing asphalt to UV, the precursor to cracking.
• Alligatoring and cracking on oxidized older surfaces.
• Open laps and seams, often where a torch ran too fast or an adhesive was applied cold.
• Failed pipe boots, pitch pockets and curb flashings.
• Splits at deck movement lines and over insulation joints.
• Ridging and buckling telegraphing the insulation joints below.
• Ponding and clogged drains, which accelerate everything above.

Repairs are made with compatible torch, cold-adhesive or self-adhered patch plies, built in layers the way the roof was built. Mod bit repairs, done right, are among the most durable in commercial roofing.

Repair when the assembly is dry and problems are isolated — blisters, laps, flashings, splits.

Coat when the surface is weathered and losing granules but not yet cracked through, and the insulation is dry. A reflective coating over a sound mod bit roof buys years, cuts surface temperature and often lands as a maintenance expense. Timing is everything: coat before cracking, not after.

Replace when moisture scanning or core cuts show wet insulation across a meaningful area, when the surface is broadly alligatored and brittle, when splits recur along the same movement lines, or when the deck is deteriorating. Note the layer limit: most jurisdictions allow two roofs on a building, and many older mod bit roofs are already the second layer over a built-up system — which forces a tear-off.

Two real objections come up on mod bit work, and both have answers.

Odor. Hot asphalt smells, and on a school, medical building or restaurant that is a genuine problem. Cold-adhesive and self-adhered systems eliminate most of it, and scheduling around occupancy handles the rest.

Open flame. Torch application is fast and produces an excellent bond, and it demands a crew that follows fire-watch protocol, keeps extinguishers staged, stops torching well before the end of the shift and walks the roof afterward. On buildings where flame is unacceptable — some schools, hospitals, historic structures, buildings with combustible decks or insurers who prohibit it — we specify self-adhered or cold-applied instead. That is a specification decision made before the crew arrives, not a field improvisation.

Restaurants and food service, schools and universities, hospitals and medical office buildings, churches, apartment and condominium properties, municipal buildings, retail, light industrial, and older low-slope buildings across this region that have carried asphalt systems for decades.

Institutional and school work leads mod bit volume around St. Louis, Columbia and Jefferson City and Indianapolis; hail claims drive much of it in Springfield, Kansas City and across Metro East and Southern Illinois; and restaurant, hotel and condominium roofs lead at the Lake of the Ozarks.

We install and service modified bitumen roofs from seven local offices covering 143 cities in Missouri, Kansas, Illinois and Indiana. Each market runs its own crews and its own number — call the office nearest the building.

• St. Louis — (314) 429-6000
• Kansas City — (816) 872-9500
• Indianapolis — (317) 726-6000
• Springfield — (417) 429-1927
• Columbia / Jefferson City — (573) 343-8993
• Lake of the Ozarks — (573) 343-8993
• Metro East & Southern Illinois — (618) 549-0800