What this covers
Modified bitumen is asphalt roofing reinforced with polymers and sold in rolls, installed as a base sheet plus a granulated cap sheet, sometimes with a mid ply. The roofer fastens or adheres the base sheet, then lays the cap in overlapping courses, bonding it with cold adhesive or self-adhering strips, or by torch on buildings where that method is appropriate and permitted. Seams are sealed and granules embedded at the laps, and the roof is flashed at parapets, curbs and drains with the same material and metal. It is thick, walkable and tolerant of foot traffic around rooftop equipment. Careful work shows in uniform laps, fully bonded seams and flashing turned up and terminated above the water line.
When to call
- A flat roof with rooftop equipment that gets regular foot traffic.
- An existing rolled or built-up roof with alligatored or bare patches.
- Open laps, blisters or exposed base sheet on a modified bitumen roof.
- A duplex or small building roof due for replacement.
What to expect
- InspectThe roofer checks the deck, insulation and drainage and selects the application method.
- PrepareOld roofing is removed, the deck repaired, and insulation and base sheet installed.
- CapThe cap sheet is laid in courses, seams bonded and granules embedded at the laps.
- FlashParapets, curbs, drains and edges are flashed and finished with metal.
Get a certified company
Look up a certified company by ZIP code. Every company's license, insurance and trades are verified before it is listed, and placement is never paid.
Questions people ask
Is torch-down safe?
It requires trained crews, fire watch and a building suited to open flame. Many companies now use cold adhesive or self-adhering sheets, which avoid flame entirely.
How does it compare with single-ply membranes?
Modified bitumen is thicker and takes foot traffic well; single-ply sheets are lighter and faster to install. Both work when installed and flashed correctly.
Can a worn cap sheet be coated?
A sound roof with surface wear can take a reflective coating to extend its life. A roof with open laps or wet insulation needs repair or replacement first.
Related: Flat roofing · EPDM rubber roofing · Roof replacement · All roofing and gutters
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