Modified Bitumen Roofing

Modified bitumen has been protecting flat roofs since the 1960s. This multi-layer asphalt system combines the proven performance of built-up roofing with modern polymer technology.

What Is Modified Bitumen?

Modified bitumen is asphalt reinforced with polymer modifiers (typically APP or SBS) that improve flexibility, durability, and temperature performance. It's applied in sheets rather than the liquid application of traditional built-up roofing.

Types of Modified Bitumen

APP (Atactic Polypropylene)

APP-modified bitumen is torch-applied:

• Excellent UV resistance
• Handles high temperatures well
• Smooth surface finish
• Requires skilled torch application

SBS (Styrene-Butadiene-Styrene)

SBS-modified bitumen offers flexibility:

• Better flexibility in temperature swings
• Multiple application methods available
• Superior elongation properties
• Self-healing in warm weather

Application Methods

Modified bitumen can be installed several ways:

• Torch-applied – Traditional method, requires experienced crew
• Cold-applied adhesive – No open flame, safer for occupied buildings
• Self-adhered – Peel-and-stick, fastest installation
• Mopped in hot asphalt – Like traditional BUR

Advantages of Modified Bitumen

Why choose mod-bit for your flat roof?

• Multi-layer protection – Redundancy if one layer is damaged
• Excellent puncture resistance – Handles foot traffic well
• Proven track record – 50+ years of field performance
• Self-healing – Minor damage seals in Florida heat
• Economical – Lower cost than single-ply membranes

Disadvantages

Modified bitumen has limitations:

• Dark surface absorbs heat – Can increase cooling costs
• Shorter lifespan than single-ply – 15-20 years typical
• Torch application fire risk – Requires careful installation
• Seams are weak points – Not as strong as heat-welded TPO/PVC

Modified Bitumen vs. Single-Ply

How does mod-bit compare to TPO or EPDM?

• Cost: Mod-bit is typically cheaper upfront
• Lifespan: Single-ply usually lasts longer
• Energy efficiency: White single-ply membranes win
• Puncture resistance: Mod-bit is superior
• Repair ease: Mod-bit is easier to patch

Cost Expectations

Modified bitumen roofing typically costs $4-$8 per square foot installed, making it one of the more economical flat roof options.

Extending Mod-Bit Lifespan

A reflective roof coating can extend modified bitumen life by 10-15 years while reducing cooling costs. This is often more cost-effective than full replacement.

Best Applications

Modified bitumen works well for:

• Budget-conscious commercial projects
• Roofs with heavy foot traffic
• Buildings needing superior puncture resistance
• Repair/restoration of existing BUR systems

Contact us to discuss whether modified bitumen is right for your project.