What these systems are
Built-up roofing (BUR) is the original flat roof: alternating layers of asphalt and reinforcing felt, usually topped with gravel. Modified bitumen is its modern descendant — factory-made sheets of asphalt modified with rubber or plastic for flexibility, torched, mopped or self-adhered in two or three plies. Both give you multiple layers of protection, which is why they tolerate foot traffic and abuse better than single-ply.
| Modified bitumen | Built-up (BUR) | |
|---|---|---|
| Installed cost / sq ft | See costs | See costs |
| Service life | 20 – 25 yrs | 20 – 30 yrs |
| Layers | 2 – 3 plies | 3 – 5 plies |
| Strength | Flexible, good impact resistance | Very durable, heavy |
| Best for | Roofs with foot traffic, smaller low-slope roofs | Large roofs where redundancy matters |
Common problems we fix
- Blisters and splits where moisture was trapped between plies
- Alligatoring — cracked, dried-out surfacing from UV exposure
- Surfacing loss exposing the asphalt below
- Failed flashing at parapets and curbs
- Hail fractures in the gravel or granule surface
Most of these are repairable. When they are widespread, a restoration coating over a dry, sound roof is often the next step before replacement.
Replacing an old BUR or mod-bit roof
Many owners replace a worn built-up roof with TPO or EPDM for lower cost and weight, and some replace like-for-like for durability. Older built-up roofs may contain asbestos in the felts or mastics, so we test before tear-off where the building age calls for it.
Frequently asked questions
Is modified bitumen better than TPO?
It is tougher under foot traffic and more forgiving of installation. TPO is lighter, cheaper on large roofs and reflective. For a roof that sees regular service traffic, mod-bit earns its place.
Can you repair a built-up roof?
Yes. Blisters, splits and flashing failures are cut out and rebuilt in layers. If insulation below is wet, that comes out first.
Why does my gravel roof leak at the edges?
Gravel stop and parapet flashings are the usual failure points on built-up roofs. They are repairable without touching the rest of the roof.
Modified bitumen & built-up roofing in: Kansas City · Topeka & NE Kansas · Metro Atlanta
