Built‑Up Roofing (BUR) vs Modified Bitumen: What's the Difference?
When choosing a roofing system for a commercial building, two popular options often come up: Built‑Up Roofing (BUR) and Modified Bitumen. While both are designed for flat or low-slope roofs, they differ in materials, installation methods, durability, and long-term value.
At Allied Roofing, we've worked with both systems extensively and understand the strengths and limitations of each. Let's break down the key differences to help building owners, property managers, and contractors make the best choice based on performance, budget, and building needs.
1. What Are BUR and Modified Bitumen?
Built-Up Roofing (BUR)
BUR has been used for over a century and is often referred to as "tar and gravel" roofing. It consists of alternating layers of bitumen (asphalt or coal tar) and reinforcing fabrics like fiberglass or felt. These layers are built up directly on the roof deck to form a multi-ply membrane. The system is then finished with a gravel or reflective cap layer for UV and weather protection.
Modified Bitumen
Modified Bitumen is a more modern alternative to BUR that combines asphalt with polymer modifiers for added flexibility and durability. These polymers—APP (atactic polypropylene) or SBS (styrene-butadiene-styrene)—enhance commercial roofing performance depending on the desired qualities (heat resistance vs. flexibility). The material is manufactured in rolls and expertly applied in one or more plies, using torch application, cold adhesives, or self-adhered membranes.
2. BUR vs. Modified Bitumen: A Detailed Comparison
While both systems are designed to protect commercial buildings from the elements, they differ in several key areas:
Installation Method
BUR systems require hot-applied asphalt, layered by hand with reinforcement felts. This process is labor-intensive, often messy, and demands highly experienced installers (like those at Allied Roofing). The result, however, is a thick, redundant barrier that excels at waterproofing.
Modified Bitumen systems are quicker and cleaner to install. While they still require professional installation, they come in pre-manufactured rolls and can be applied using several methods—torch-down heat, cold adhesive, or peel-and-stick application. This makes them ideal for buildings where minimizing business disruption is critical.
Commercial Roofing Lifespan and Durability
BUR roofs are known for longevity and strength. A properly installed and maintained BUR commercial roofing system can last 30 years or more. Its multiple layers provide excellent protection against water intrusion, UV rays, and mechanical damage.
Modified Bitumen also offers solid performance, but it typically has a lifespan of 15 to 25 years. SBS-modified versions are especially valued for their ability to expand and contract in response to temperature swings, which helps prevent cracking and premature aging.
Weight and Structural Load
BUR systems are significantly heavier than Modified Bitumen due to their multi-layer composition and gravel topping. Some buildings may require structural evaluation or reinforcement before installing a BUR roof.
Modified Bitumen is lightweight by comparison, making it suitable for a broader range of buildings—especially older structures or those with weight restrictions.
Weather and Climate Performance
BUR performs extremely well in hot climates and under prolonged sun exposure, particularly with a gravel or reflective surface. Its heavy mass and thickness help resist UV degradation and heat-related damage.
Modified Bitumen, particularly SBS-modified products, is ideal for regions with frequent temperature fluctuations or freeze-thaw cycles. Its flexibility helps it resist cracking and splitting under thermal stress.
Maintenance and Inspection
BUR roofs typically require less frequent inspection once installed, though spotting problems beneath gravel can be more challenging. Repairs can be more involved due to the built-up nature of the system.
Modified Bitumen roofs require more routine inspection, especially at seams and flashing points. However, their surface makes it easier to identify damage or wear, and patching is relatively straightforward.
Fire Resistance
Both systems offer good fire resistance when properly installed. BUR systems, especially those finished with gravel, have excellent fire ratings. Modified Bitumen roofs can also achieve high fire performance ratings with the right cap sheets and installation methods, though caution is needed with torch-applied applications.
Commercial Roofing Cost: BUR vs. Modified Bitumen
BUR roofs tend to have higher upfront costs due to labor, materials, and time required for installation. However, their long lifespan may justify the investment over time.
Modified Bitumen systems generally offer lower initial costs and faster installation, making them attractive for budget-conscious projects or where building downtime must be minimized.
3. Pros and Cons Overview
Built-Up Roofing (BUR)
Pros:
- - Long lifespan (up to 30–40 years with maintenance)
- - Exceptional waterproofing from multiple layers
- - High resistance to UV rays and foot traffic
- - Excellent fire protection, especially with a gravel surface
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Cons:
- - The extra weight may require structural upgrades
- - Time-consuming and labor-intensive installation
- - Higher upfront cost
- - Difficult to locate issues under the gravel surface
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Modified Bitumen
Pros:
- - Flexible in varying temperatures (especially SBS-modified)
- - Faster, cleaner installation with multiple application options
- - Lightweight, reducing structural strain
- - Easier to repair and inspect
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Cons:
- - Slightly shorter lifespan compared to BUR
- - Vulnerable at seams and flashing points if not properly sealed
- - May require more frequent maintenance
- - Torch-down methods can present a fire risk if not professionally handled, making it more essential to find a commercial roofing specialist you can trust
4. Which System Is Right for Your Building?
The ideal roofing system depends on your specific building needs, location, and budget:
- - Choose BUR if your building can handle the weight, you're located in a hot climate, and you want maximum durability and longevity.
- - Choose Modified Bitumen if you need a faster, more flexible, and cost-effective solution, particularly in areas with significant temperature variation or on buildings where weight is a concern.
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If you're still unsure which is right for your property, a professional inspection and consultation can help determine the best system based on your roof's size, slope, exposure, and structural capacity.
Why Choose Allied Roofing for Your Flat Roofing Needs?
At Allied Roofing, we've installed, maintained, and repaired thousands of commercial roofing systems throughout North Carolina. Our team has decades of experience working with both BUR and Modified Bitumen, and we take pride in delivering long-lasting, high-performance solutions tailored to your building.
From detailed inspections and recommendations to expert installation and maintenance, Allied Roofing partners with you every step of the way—protecting your investment and your peace of mind. We proudly serve businesses in Kernersville, Winston-Salem, and beyond. You can explore our work or contact our roofing experts to get started today!
Allied Roofing: Commercial Roofing Services in Kernersville, NC
When you need commercial roofing solutions you can trust, turn to Allied Roofing. Our local Kernersville experts collaborate with you, assessing your budget, needs, and priorities to help you find the best commercial roofing solutions for you. Once we tailor our solutions to your needs, we work to get lasting jobs done. You can explore our work or contact our professionals to get started today.
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