If you’ve got a flat or low-slope roof and you’re weighing up your options, you’ve probably come across Built-Up Roofing (BUR) and Modified Bitumen (Mod Bit). But what exactly sets them apart? And which one is right for your building?
In this guide, we’ll walk you through the 8 differences between Built-Up Roof vs Modified Bitumen—so you can make a smart, confident choice for your next roofing project.
What Are Built-Up Roof and Modified Bitumen Roofs?
Before we dive into the differences, let’s get clear on what each roofing system actually is.
Built-Up Roof (BUR): The Classic Option
BUR has been around for over a century. It’s a reliable, tried-and-tested system made up of alternating layers of bitumen (a sticky, tar-like substance) and reinforcing fabrics, like felt. These layers are built up—hence the name—and topped with gravel or a reflective coating.
Modified Bitumen (Mod Bit): The Modern Take
Modified Bitumen is a newer approach that improves on the BUR concept. It uses factory-made rolls of modified asphalt (think of it like supercharged bitumen) that are installed in overlapping sheets. Installation is faster and can be done with heat or even peel-and-stick methods.
What are the Differences Between Built-Up Roof vs Modified Bitumen?
Let’s break it down and compare these two systems side by side.
1. Construction and Materials
- BUR: Built layer by layer using alternating bitumen and reinforcement sheets, topped with gravel or a reflective finish.
- Mod Bit: Pre-made sheets of modified asphalt rolled out in one or two layers, secured with heat, adhesive, or self-adhesive backing.
2. Durability and Lifespan
- BUR: Exceptionally durable and capable of lasting 20–30 years or more with proper installation.
- Mod Bit: Strong but may wear faster, typically lasting 15–25 years depending on weather and maintenance.
3. Flexibility and Movement Tolerance
- BUR: Not very flexible once installed—can crack in environments with large temperature fluctuations.
- Mod Bit: Offers better elasticity and movement, making it ideal for regions with freeze-thaw cycles or frequent expansion and contraction.
4. Weight Load
- BUR: Heavy due to multiple thick layers and gravel. Not ideal for buildings with structural weight concerns.
- Mod Bit: Lightweight and much easier on the building’s structure, making it suitable for a wider range of properties.
5. Installation Speed and Labour Requirements
- BUR: Time-consuming and labour-intensive. Requires skilled workers and more site preparation.
- Mod Bit: Quicker to install thanks to its factory-made sheets. Can often be installed with a smaller team and less specialised labour.
6. Maintenance and Repairs
- BUR: Once installed properly, it needs little maintenance. Repairs can be more involved due to the layered structure.
- Mod Bit: Requires more routine maintenance and checks, particularly for UV protection and seam integrity, but repairs are often simpler.
7. Waterproofing Performance
- BUR: Excellent at resisting leaks because of its multi-layer system and heavy-duty surface materials.
- Mod Bit: Very good waterproofing as well, with an edge in resisting punctures—especially useful in high foot-traffic areas or if rooftop equipment is present.
8. UV and Heat Resistance
- BUR: Gravel or a reflective top layer acts as natural sun protection.
- Mod Bit: May need an additional UV-protective coating depending on the climate and exposure level.
What Are the Pros and Cons of Built-Up Roof vs Modified Bitumen?
Built-Up Roof (BUR)
Pros:
- Extremely durable and reliable
- Excellent at waterproofing
- Low maintenance once installed
Cons:
- Heavier structure
- Slower installation process
- Higher upfront labour costs
Modified Bitumen (Mod Bit)
Pros:
- Lightweight and flexible
- Faster and more affordable to install
- Great for puncture-prone roofs
Cons:
- Shorter average lifespan
- Needs regular inspections and possible re-coating
- Some methods require heat or special tools
How Are They Installed?
BUR Installation Steps:
- Inspect the roof deck
- Install insulation and vapour barrier (if required)
- Apply base sheet, then alternate bitumen and felt layers
- Finish with gravel or protective coating
Mod Bit Installation Steps:
- Inspect roof deck (less worry about load-bearing)
- Add insulation as needed
- Roll out Mod Bit sheets, secure with chosen method (torch, adhesive, or peel-and-stick)
- Add a cap sheet, often with embedded granules for UV resistance
How Do You Maintain These Roofing Systems?
Whichever system you choose, regular maintenance is key to extending its lifespan:
- Schedule inspections twice a year and after major storms
- Clear debris from the roof surface and drainage points
- Watch out for standing water or blistering
- Seal cracks and reapply coatings as needed
Even a small issue, like a loose seam, can turn into a big problem if left unchecked—so staying on top of it pays off.
Still Not Sure Which Roof is Right?
Choosing between BUR and Mod Bit really depends on your building’s needs. If you value longevity and don’t mind the longer installation time, BUR might be ideal. On the other hand, if speed, flexibility, and lower weight are priorities, Mod Bit is worth serious consideration.
At HP Roofing, we’ve helped countless property owners navigate the roofing process—from selecting the right material to expert installation and maintenance. No matter which system you choose, we’ll ensure it’s done right the first time.
Get in touch with our team today for expert advice and a no-obligation quote.
Conclusion:
To wrap it all up, the difference between Built-Up Roof vs Modified Bitumen comes down to structure, flexibility, installation time, and longevity. BUR gives you a tough, layered defence that’s stood the test of time. Mod Bit, on the other hand, offers modern flexibility, quicker installation, and a lighter touch on your building.
By understanding the 8 differences between Built-Up Roof vs Modified Bitumen, you’re now better equipped to choose a roofing solution that fits your building, budget, and long-term needs.
Still have questions? Contact HP Roofing today and let’s discuss the best option for your roof.
