Modified Bitumen (“Mod Bit”) evolved from asphalt roofing. It consists of asphalt reinforced with fiberglass or polyester, supplied in rolls. It is applied in layers (base sheet + cap sheet).
- The Pros: It is thick and tough, resisting foot traffic better than single-ply membranes. It matches the aesthetic of shingle roofs better than white plastic sheets.
- The Cons: It relies on lap-seams which can be a weak point. Installation often involves open-flame torches (fire risk).
Mod Bit is common for residential flat sections (like porches or garage transitions) in Texas. It creates a robust multi-layer system that handles the occasional branch impact well. SBS (rubber-modified) blends are preferred here over APP (plastic-modified) because they handle the thermal expansion/contraction cycles of Texas weather better.