Roofing systems · SBS
Modified Bitumen Roofing Ottawa
SBS modified bitumen is a multi-ply asphalt-based roofing system. It's tough, familiar and redundant — and it comes with specific installation and safety considerations.
The short answer
Modified bitumen roofing uses asphalt modified with SBS (styrene-butadiene-styrene) rubber, reinforced and installed in layers — typically a base sheet and a granule-surfaced cap sheet. The two plies give redundancy and a durable surface for foot traffic. Sheets can be torch-applied, self-adhered, hot-mopped or set in cold adhesive. We repair SBS roofs and include it among the options for replacements after an assessment.
SBS in Ottawa's freeze-thaw climate
SBS rubber gives the asphalt flexibility, which helps it cope with cold-weather movement. The multi-ply build-up means a defect in one ply doesn't automatically mean a leak. Freeze-thaw cycles still work on laps, flashings and any blistering, so detailing and drainage remain essential.
Installation methods and safety
Torch-applied SBS is common but involves open flame and real fire risk; it's specialized work that must be avoided near combustible materials and is often replaced by self-adhered or cold-adhesive methods at sensitive details, on wood-frame additions or where fire risk is unacceptable. The method should be chosen for the building, not by habit.
Seams, flashing, drainage and insulation
Laps
Side and end laps are bonded by heat, adhesive or self-adhesion. Laps should be offset between plies so seams don't line up.
Flashing
Two-ply SBS flashings run up walls and parapets and are typically protected by metal counter-flashing. Cracked or loose flashings are a common leak source on older roofs.
Drainage
Granule loss and blistering are accelerated by ponding. Correct slope to drains is as important as the membrane.
Insulation
SBS is often installed over protection board on rigid insulation. Replacements are a chance to add insulation and taper.
Repairing SBS: what's compatible
SBS is repaired with compatible modified bitumen membrane and mastics. It's not compatible with single-ply materials like TPO or EPDM without specific transition details. Blisters, split laps and cracked flashings can usually be repaired; widespread granule loss, cracking across the field or saturated insulation suggest the roof is near the end of its life.
Pros and cons
- Pro: two plies provide redundancy
- Pro: tough, granule-surfaced cap stands up to foot traffic
- Pro: familiar to many trades and widely repairable
- Con: heavier than single-ply systems
- Con: torch application carries fire risk
- Con: more labour-intensive to install
Quote cost factors
Size and shape of the roof; whether existing roofing must be removed; the condition of the deck; insulation type and thickness; the number of drains, penetrations and curbs; parapet and wall flashing height; access and hoisting; and the season. We don't publish flat prices because these vary widely from roof to roof.
Maintenance
Keep drains clear, watch for blisters and granule loss, and have flashings and counter-flashings checked after winter. Avoid improvised patches with incompatible products, which make later repairs harder.
References: City of Ottawa — Do I need a building permit? · NRC Energy RCI
Frequently asked questions
Is modified bitumen the same as a tar-and-gravel roof?
No. Built-up tar-and-gravel roofs use multiple layers of felt and hot asphalt with a gravel surface. Modified bitumen uses factory-made rubberized sheets, usually two plies.
Does SBS always need a torch?
No. Self-adhered and cold-adhesive SBS products are available and often preferred where fire risk is a concern.
Can you add a single-ply patch to an SBS roof?
Not directly. SBS should be repaired with compatible modified bitumen materials, or with a properly designed transition.
Next step
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