What Is Modified Bitumen Roofing?
Modified bitumen is asphalt reinforced with polymers — SBS rubber for elasticity or APP plastic for UV and heat tolerance — factory-built into thick rolls on polyester or fiberglass reinforcement, usually surfaced with granules. Crews install it in overlapping courses over a base sheet, bonding the laps by torch flame, hot asphalt, or peel-and-stick adhesive; the melted or adhered lap becomes the waterproof joint. Its virtue on low-slope porches, additions, and transitions is toughness: it tolerates foot traffic and hail far better than thin single-ply membranes, and it flexes with building movement where unmodified asphalt would crack. It fails at laps that were under-heated or contaminated, at blisters where moisture was trapped beneath, and by alligatoring as decades of UV dry the surface. Homeowners spot open lap edges, bubbles, or granule-bare patches. Repairs patch well — the material welds to itself — while torch application carries real fire risk and belongs only with insured, trained crews.
Important Distinction
Note: Modified bitumen is a heavy engineered membrane system, not the thin bargain 'roll roofing' sold for sheds — the two look similar from a distance and get conflated in quotes and DIY advice.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Modified Bitumen Roofing Relates to Other Topics
Modified bitumen is asphalt-based and applied in torched or self-adhered rolls; TPO is a single-ply plastic sheet with welded seams - they fail differently, and repair materials for one do not bond to the other, so misidentifying the membrane wastes the patch.
Asphalt-based membranes age fastest under standing water: on granule-surfaced modified bitumen, ponds strip the surfacing first, so a bald patch in a low spot is the pond announcing itself even when dry.
Related To Modified Bitumen Roofing
Modified bitumen is the built-up roof's successor: BUR's alternating plies of felt and hot asphalt, factory-laminated into a roll - so an old gravel-topped BUR is usually replaced with mod-bit or single-ply, not rebuilt in kind.
Questions about Modified Bitumen Roofing?
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