Modified Bitumen Roofing
Modified Bitumen is an asphalt-based roofing membrane enhanced with polymer modifiers to improve performance characteristics. Bridging traditional built-up roofing with single-ply technology, modified bitumen combines the proven reliability of multi-ply systems with modern manufacturing and installation techniques, offering excellent durability, flexibility, and tensile strength for commercial and low-slope applications.
Composition
Specialized material designed for weather protection and durability on building roofs
Properties
Thickness
120-180 mil (0.120"-0.180")
Total system thickness typically ranges from 120-180 mil depending on the number of plies and specific products used. Individual sheets range from 3-5 mm (120-200 mil) in thickness.
Weight
1.0-3.0 lbs/ft²
System weight varies significantly based on the number of plies, surfacing, and specific products. A typical two-ply system weighs approximately 1.5-2.0 lbs/ft², while systems with multiple plies and heavy granular surfacing can approach 3.0 lbs/ft².
Tensile Strength
50-130 lbf/in
Varies by product and reinforcement type. Polyester-reinforced membranes typically offer higher tensile strength (80-130 lbf/in) than fiberglass-reinforced products (50-90 lbf/in).
Low Temperature Flexibility
SBS: -25°F to -40°F, APP: 0°F to -10°F
SBS-modified membranes maintain flexibility at much lower temperatures than APP-modified products, making them more suitable for cold climate installations and areas with extreme temperature fluctuations.
Fire Rating
Class A, B, or C (ASTM E108)
Rating depends on the complete roof assembly including deck, insulation, and surfacing. Systems with mineral granule or fire-resistant surfacing typically achieve Class A ratings.
Solar Reflectance Index (SRI)
Dark: 5-25, White/Reflective: 50-85
Traditional mineral-surfaced modified bitumen has relatively low solar reflectance. However, products with white granules, reflective coatings, or foil facings can achieve much higher SRI values, meeting cool roof requirements.
Applications
Commercial Buildings
Widely used on office buildings, retail centers, warehouses, and other commercial structures with low-slope or flat roofs, particularly where proven performance and redundancy are priorities.
Institutional Facilities
Common on schools, universities, hospitals, and government buildings where long-term performance, reliability, and ease of maintenance are critical considerations.
Multi-Family Residential
Applied to apartment buildings, condominiums, and other multi-family structures with flat or low-slope roof areas, providing a durable solution with good puncture resistance for roofs with moderate traffic.
Reroofing and Recover Applications
Frequently used for recovering existing built-up roofing (BUR) or modified bitumen systems, avoiding costly tear-off and disposal while upgrading performance.
Hybrid Roofing Systems
Often combined with other roofing technologies such as fluid-applied membranes or single-ply systems in hybrid applications that leverage the strengths of each material for specific roof areas or conditions.
Cold Climate Applications
SBS-modified systems are particularly well-suited to regions with extreme cold temperatures and significant thermal cycling due to their exceptional flexibility and elongation at low temperatures.
Advantages
- Multi-ply redundancy reducing the risk of leaks from single-point damage
- Excellent tensile strength and tear resistance, particularly with polyester reinforcement
- High puncture resistance compared to many single-ply systems
- SBS types offer exceptional flexibility in cold temperatures
- Proven track record with performance history exceeding 40 years
- Multiple installation methods providing application flexibility
- Self-healing properties for minor cuts and abrasions (particularly SBS types)
- Compatible with many existing roof systems for recover applications
- Granule-surfaced options provide excellent foot traffic resistance
Limitations
- Traditional application methods (hot asphalt, torch) involve fumes, odors, and fire risks
- Higher labor intensity than single-ply installation
- Performance varies significantly based on installation quality
- Dark surfaces absorb heat, potentially increasing cooling loads
- Seams rely on proper adhesion rather than molecular bonding
- APP types can become brittle in very cold conditions
- Higher weight than single-ply systems
- Petroleum-based product with associated environmental considerations
- Limited recyclability at end of service life
Sustainability Profile
Sustainable roofing options include recycled materials, cool roofs that reduce energy consumption, and living roofs that provide insulation and manage stormwater. Durability is a key factor in sustainability assessment.