Start with seams, drainage and details.
Low-slope roofing uses assemblies designed for a different water-shedding environment than steep-slope shingles. Compare the membrane, attachment, insulation and drainage arrangement together. The product name alone does not describe the complete roof or resolve existing drainage and moisture concerns.
TPO in plain language
Thermoplastic polyolefin, or TPO, is a single-ply membrane with heat-welded seams. A proposal should identify the membrane specification, attachment method and details around rooftop equipment. Ask how the complete assembly fits the existing deck and roof conditions.
Modified bitumen in plain language
Modified-bitumen systems use asphalt-based membranes modified with polymers. Assemblies and application methods vary, including self-adhered products. Ask for the actual system and layers specified for your building, rather than comparing only the visible cap sheet.
Water needs a route off the roof
Discuss where water collects, how outlets are maintained and whether the proposal changes drainage. Identify which items are being repaired and which existing conditions remain. Include service paths for equipment so future visits do not become an afterthought.
