What modified bitumen means
Modified bitumen is a low slope roofing sheet made of asphalt blended with rubber or plastic modifiers. It is torched, mopped, cold glued or self adhered in layers.
Also called mod bit, torch down.
Where it matters on a roofing job
Torch applied mod bit needs fire watch and insurance that covers open flame work, so check your policy before you bid it. Many residential flat roofs over porches and additions are mod bit.
What the model code says
- Modified bitumen roofing needs a design slope of at least one-fourth unit in 12 for drainage. (IRC 2021, Chapter 9)
Check which code edition your building department enforces for modified bitumen before you quote.
What it costs
For modified bitumen, the closest koira.ai price is the flat roof replacement cost guide, near $9,800 for a typical job and $6,800 to $21,000 for most. The guide shows its sources and what moves the price.
Work it out
- Cost guide: Flat roof replacement cost
- Licensing: Roofing license rules by state
- Tools, templates and guides: Free roofing resources
Sources: 2021 International Residential Code, Chapter 9, Roof Assemblies (ICC). Checked October 9, 2026.