A Tough Roof for Working Buildings
Modified bitumen, or "mod bit," is an asphalt roof reinforced with polyester or fiberglass and modified with rubber or plastic polymers so it stays flexible. It's typically installed in two or more layers, which gives it a thickness single-ply roofs don't have. That's why it's common on buildings with a lot going on up top: HVAC units, exhaust fans, satellite equipment, and techs walking to all of it.
In St. Charles County, you'll find it on older office parks, schools, retail buildings, and churches, often installed in the 1990s and 2000s. Many of those roofs are now at the age where they need real attention.
Modified Bitumen Services
Repairs
We repair blisters, split laps, cracked flashing, worn areas around equipment, and damage from hail or dropped tools. Repairs are made with compatible modified bitumen materials so they bond to the existing roof instead of sitting on top of it.
Restoration coatings
A mod bit roof that's lost its granules and started to crack but is still dry underneath is often a strong candidate for a coating. It seals the surface, reflects heat, and can add years for much less than replacement.
Replacement
When a modified bitumen roof is wet throughout or at the end of its life, we'll give you options: a new mod bit system, or a switch to TPO or another membrane if that suits the building better. We'll explain the tradeoffs either way.
Warning Signs on a Mod Bit Roof
- Bare spots where granules have washed away, especially near downspouts and scuppers
- Blisters or bubbles in the surface
- Cracks or "alligatoring" across the top layer
- Laps or seams that have opened at the edges
- Flashing pulling away from parapet walls and curbs
Granules in the gutters? A heavy buildup of granules in gutters or around drains means the top surface is wearing out and the asphalt underneath is exposed to the sun. That's the right time to look at repair or a coating, before leaks start.
Getting Started
We'll inspect the roof for free, check for moisture under the surface, and send you photos and written options. If a repair or coating will do the job, we'll tell you. If replacement is the better value, we'll show you why.
Modified Bitumen Questions
What is a modified bitumen roof?
It's an asphalt-based roof made of reinforced sheets, usually installed in two or more layers. The top layer often has granules, similar to shingles, that protect it from the sun. It's common on older office, retail and school buildings.
How long does modified bitumen last?
Modified bitumen roofs commonly last 15 to 25 years. Multi-ply systems, good drainage and regular maintenance push them toward the longer end.
Can a modified bitumen roof be repaired?
Yes. Blisters, split seams, worn granules and flashing failures are usually repairable with compatible materials. If the roof is aging overall but dry underneath, a coating can extend its life.
Is modified bitumen good for roofs with a lot of foot traffic?
It's one of the better choices. The multiple layers make it more puncture resistant than single-ply membranes, so it holds up well on roofs where HVAC technicians and other trades walk often.