What is modified bitumen roofing?
Modified bitumen is asphalt mixed with rubber or plastic polymers and laid in overlapping rolls, creating a flexible, durable roofing membrane for low-slope commercial and residential buildings.
Modified bitumen roofing consists of asphalt reinforced with elastomeric or plastomeric polymers (typically SBS or APP), delivered in roll form and heat-welded or adhesive-bonded to the roof substrate. The polymer modification makes the material more flexible and resistant to cracking than conventional bitumen, especially in Ontario's temperature swings between winter freeze and summer heat.
This system sits between built-up tar and gravel roofing (which uses multiple layers of tar and aggregate) and synthetic membranes like PVC or TPO. Unlike tar and gravel, modified bitumen requires fewer plies to achieve comparable durability and produces less waste during installation. The rolls are typically 3 to 4 feet wide and torch-applied or cold-adhesive-applied to create a waterproof seal.
Modified bitumen works well on low-slope or flat roofs common in commercial buildings, warehouses, and multi-unit residential properties across Ontario. The material performs best when installed by trained applicators who ensure proper overlap and heat bonding to avoid leaks and premature deterioration. Maintenance involves periodic inspections for punctures, seams, and flashing condition.
When shopping for flat roofing contractors, asking whether they offer modified bitumen installation helps narrow choices to applicators with the right equipment and experience for this specific membrane type.