Flat or low-slope roof projects come with plenty of decisions, and choosing the right material is one of the big ones.
Modified bitumen and roll roofing both show up as options, but they serve very different needs.
Whether you’re looking for long-term durability or something quick and cost-effective, we’ll break down what each option brings to the table so you can make the right call for your roof.
Quick Overview: Modified Bitumen vs Roll Roofing
| Feature | Modified Bitumen | Roll Roofing |
|---|---|---|
| Lifespan | 15–30 years | 5–15 years |
| Installation | Professional, multi-layer | DIY-friendly, single-layer |
| Materials | Polymer-modified asphalt | Asphalt felt or fiberglass |
| Weather Resistance | Excellent | Basic |
| Cost | Higher upfront | Lower upfront |
| Best For | Long-term protection | Temporary/small structures |
What is Modified Bitumen Roofing?
Modified bitumen is a type of asphalt roofing that’s been, well, modified – by adding rubber or plastic polymers to improve its strength, flexibility, and weather resistance.
It’s usually installed in two or three layers using heat (torch-down), cold adhesives, or self-adhesive membranes. Those layers make it incredibly resilient, and with proper installation, it can last 20+ years.
Best for:
Commercial buildings, flat-roofed homes, garages, and any structure where durability and waterproofing matter.
What is Roll Roofing?
Roll roofing (or rolled roofing) is a more basic asphalt-based product that comes in large rolls. It’s often made of asphalt-saturated felt or fiberglass with a top layer of mineral granules for UV protection.
It’s usually applied in a single layer and either nailed, glued, or self-adhered. It’s easy to install – especially for small or temporary structures – but it just doesn’t hold up as well long-term.
Best for:
Sheds, garages, low-cost or temporary buildings, and quick patch jobs.
Materials & Construction Differences
Modified Bitumen Materials:
- Polymer-modified asphalt (SBS or APP)
- Reinforcement layers like polyester or fiberglass
- Multi-ply systems (2- or 3-layer)
Roll Roofing Materials:
- Asphalt-saturated organic felt or fiberglass
- Coated with asphalt and topped with mineral granules
- Single-layer application
The added polymers in modified bitumen (such as SBS for flexibility or APP for UV resistance) give it a serious edge in tough climates. Roll roofing, however, is more brittle, more prone to cracking, and less protective—especially over time.
Installation Process: Time, Tools & Skill Required
Modified Bitumen Installation:
- Labor-intensive and best left to pros
- Requires special equipment: torches, rollers, safety gear
- Methods: torch-down (open flame), cold adhesive, or self-adhesive sheets
- Seams are sealed with heat or adhesives for waterproofing
- Takes longer but creates a tough, layered barrier
Roll Roofing Installation:
- DIY-friendly and quick
- Rolled out in strips and fastened with nails or adhesives
- Seams sealed with roofing cement
- Requires basic tools: hammer, utility knife, cement
- Less time, less hassle – but lower durability
Cost Comparison
| Roofing Type | Installed Cost (per sq ft) | Labor | Materials |
|---|---|---|---|
| Modified Bitumen | $4.00–$7.50 | $2.30–$4.00 | $0.70–$2.20 |
| Roll Roofing | $2.00–$5.50 | $1.50–$4.00 | $0.50–$1.50 |
Modified bitumen has a higher upfront price tag, but that comes with significantly longer lifespan and better performance. Roll roofing is more affordable to install, especially if you’re doing it yourself, but the total cost over time often adds up.
Don’t forget hidden costs: Roof deck prep, tear-off, flashing, permits, and potential safety measures (especially with torch-down) can add to the final number.
Durability, Lifespan & Maintenance
Modified Bitumen:
- Lifespan: 15 to 30 years
- Resistant to cracking, impact, UV damage
- Easy to maintain and patch professionally
- Requires occasional inspection and sealing
Roll Roofing:
- Lifespan: 5 to 15 years
- More prone to granule loss, cracking, and leaks
- Requires frequent patching, especially in bad weather
- Shorter service life means more frequent replacement
Weather & Climate Performance
Extreme Temperatures:
- Modified bitumen (especially SBS) stays flexible in freezing temps and resists cracking.
- Roll roofing tends to become brittle in cold weather and can crack under thermal expansion.
Waterproofing:
- Modified bitumen excels with welded seams and multi-layer waterproofing.
- Roll roofing provides basic protection but is more vulnerable to leaks.
UV Protection:
- Modified bitumen with APP polymers and reflective coatings handles sun exposure well.
- Roll roofing degrades faster in direct sunlight.
If you live somewhere hot, cold, wet, or windy (so, almost everywhere), modified bitumen is going to give you more peace of mind.
Roof Slope, Structure Size & Compatibility
Roof Slope:
- Modified bitumen works great for low-slope and even some steep-slope roofs.
- Roll roofing should only be used on very low slopes – ideally under 3:12.
Building Size:
- Modified bitumen is suited for large or small buildings and can cover wide flat roofs efficiently.
- Roll roofing is better for small surfaces – like garden sheds, carports, or lean-tos.
Trying to use roll roofing on a large home or commercial roof is like putting bicycle tires on a pickup truck. It might hold up briefly, but it’s not built for it.
Energy Efficiency & Environmental Considerations
Modified Bitumen:
- Reflective granules and coatings can lower cooling costs
- Less frequent replacement means less landfill waste
- APP-modified systems often qualify for cool roof ratings
Roll Roofing:
- Limited energy efficiency
- Shorter lifespan leads to more frequent disposal
- Not typically rated for reflectivity or cool roof benefits
When to Choose Which Roofing Type
Go with Modified Bitumen if you:
- Need long-term weather protection
- Own a commercial building or flat-roofed home
- Want better energy efficiency and fewer repairs
- Live in an area with harsh climate conditions
Go with Roll Roofing if you:
- Are roofing a small structure (shed, garage, workshop)
- Need a fast, affordable patch or temporary roof
- Have a very tight budget
- Are comfortable with DIY installation
Common Mistakes to Avoid
- Choosing roll roofing for a primary home or commercial building
- Skipping roof deck prep and flashing
- Using the wrong roofing type for your slope or climate
- Underestimating labor or tool needs for modified bitumen
- Focusing only on upfront cost without thinking about lifecycle value
Frequently Asked Questions
Can modified bitumen or roll roofing be installed over an existing roof?
Modified bitumen can sometimes be installed over one existing layer if the surface is sound and local codes allow it. Roll roofing is generally used for new or temporary roofs – overlaying it isn’t recommended due to seam and adhesion issues.
Are there different colors or finishes available for either roofing type?
Modified bitumen comes in a range of surface finishes, including reflective coatings and mineral granules in different colors. Roll roofing also comes in limited colors, but most are standard grey or black with fewer aesthetic options.
Does either roofing type qualify for tax credits or energy rebates?
Some APP-modified bitumen systems with cool roof ratings may qualify for local energy efficiency rebates. Roll roofing usually doesn’t qualify due to lower reflectivity and shorter lifespan.
How noisy are these roofs during rain or hail?
Both roofing types are quieter than metal roofing, but modified bitumen tends to dampen sound better thanks to its layered construction. Roll roofing has less insulation value and may transfer more noise into the structure.
Conclusion
When it comes to modified bitumen vs roll roofing, the biggest difference comes down to durability, longevity, and what kind of structure you’re dealing with.
Modified bitumen is built to last – layered, reinforced, and tough enough for commercial buildings and flat-roofed homes alike. Roll roofing? It’s quicker, cheaper, and fine for sheds, garages, or short-term fixes, but you’ll likely be replacing it sooner than you’d like.
The upfront savings often catch up to you in repairs and wear. Not sure which way to go? Book a free appointment with us! We’ll take a look at your roof, consider your slope, climate, and budget, and give you clear recommendations – no pressure, just honest advice that fits your goals.