Hot Mop Roofing in
Watsonville, CA.

Hot mop roofing — also called built-up roofing, or BUR — is constructed on site rather than arriving as a pre-manufactured sheet. A roofer applies alternating layers of hot, melted asphalt and reinforcing felt or fiberglass ply directly to the roof deck, building up two, three or four plies into a single continuous membrane. A final layer of gravel, mineral cap sheet, or reflective coating typically finishes the surface.

It's one of the oldest continuously used flat-roofing methods, and it's become less common as single-ply membrane systems (like TPO and PVC) have taken over a lot of the market — those install faster and don't require handling hot asphalt on site. That's part of why fewer roofing companies still offer it. The tradeoff is that a properly built hot mop roof creates a thick, redundant, puncture-resistant membrane that some property owners specifically want for that reason.

A localized blister, a small crack, or a single worn patch can usually be cut out and rebuilt in place without touching the rest of the roof. Widespread alligatoring across the whole surface, ponding damage that's spread to multiple areas, or a roof that's simply reached the end of its expected service life are the situations where a full tear-off and rebuild — or a switch to a different flat-roof system — makes more sense. We inspect before recommending either direction, and we won't tell you hot mop is automatically the better choice over modern single-ply systems; it depends on your roof, your budget and what you're trying to get out of it.