Built-Up Roofing (BUR) for Commercial Buildings

What Is Built-Up Roofing?

Built-up roofing, often referred to as BUR or tar and gravel roofing, is one of the oldest and most proven commercial roofing systems in use today. BUR systems have been protecting commercial and industrial buildings for well over a century, and they remain a top choice for building owners who value reliability and redundant waterproofing protection. The system earns its name from its method of construction: multiple layers of roofing materials are literally built up on the roof deck to create a thick, durable, monolithic waterproofing membrane.

A built-up roof consists of alternating layers of bitumen, which serves as the waterproofing agent, and reinforcing fabrics known as ply sheets or felts. These layers are stacked and bonded together to form a continuous membrane that is highly resistant to water penetration, foot traffic, and mechanical damage. The number of plies in a BUR system typically ranges from three to five, with more plies providing greater durability and longer service life.

Multi-Layer Construction: How BUR Works

The strength of built-up roofing lies in its layered construction methodology. Each component in the system serves a specific function, and together they create a roofing assembly with built-in redundancy that few other systems can match.

Base Sheet

The foundation of a BUR system is the base sheet, which is either mechanically fastened or adhered to the roof deck or insulation substrate. The base sheet provides a stable foundation for the subsequent ply layers and helps distribute stress evenly across the membrane assembly. In modern BUR installations, fiberglass-reinforced base sheets have largely replaced the organic felt products used in older systems, providing improved dimensional stability and fire resistance.

Ply Sheets and Bitumen Layers

Above the base sheet, alternating layers of hot bitumen and reinforcing ply sheets are applied in succession. The bitumen, typically hot-mopped asphalt, serves as both the adhesive that bonds the layers together and the primary waterproofing component. Each ply sheet adds structural reinforcement and additional waterproofing capability. A standard three-ply BUR system provides excellent protection for most commercial applications, while four-ply and five-ply systems are specified for buildings that demand maximum durability and the longest possible service life.

Surface Protection

The top layer of a BUR system provides protection against UV radiation, weather exposure, and physical damage. Several surface options are available depending on the building's requirements. Aggregate surfacing, consisting of smooth river gravel or slag embedded in a flood coat of bitumen, is the traditional choice and provides excellent UV protection, fire resistance, and resistance to foot traffic. Mineral-surfaced cap sheets offer a lighter-weight alternative with similar protective properties. Reflective aluminum or elastomeric coatings can be applied over BUR systems to improve energy performance by reflecting solar radiation.

Benefits of Built-Up Roofing

Redundant Waterproofing

The multi-layer construction of BUR provides an inherent advantage that single-ply membrane systems cannot replicate. With three to five waterproofing layers working together, a BUR system offers built-in redundancy. Even if one layer is damaged by foot traffic, mechanical equipment, or weather events, the remaining layers continue to provide waterproof protection. This redundancy is one of the primary reasons that building owners and facility managers continue to specify BUR for critical applications where leak prevention is paramount.

Proven Track Record

No other commercial roofing system can match the historical track record of built-up roofing. BUR has been used on commercial buildings since the mid-1800s, and the fundamental principles of its construction have remained consistent because they work. Decades of real-world performance data provide building owners with confidence that a properly installed BUR system will deliver reliable protection for the long term.

Excellent Foot Traffic Resistance

Built-up roofs, particularly those with gravel surfacing, provide superior resistance to foot traffic and mechanical damage. This makes BUR an excellent choice for buildings with rooftop HVAC equipment, satellite dishes, or other installations that require regular maintenance access. The thick, reinforced membrane assembly absorbs impact and resists punctures far better than many single-ply membrane systems.

Fire Resistance

Aggregate-surfaced BUR systems achieve the highest fire ratings available for commercial roofing. The gravel surface is completely non-combustible and provides an effective barrier against external fire exposure. This superior fire resistance makes BUR a preferred choice for industrial facilities, warehouses, and other buildings where fire protection is a critical concern.

BUR Maintenance and Inspection

Regular maintenance is essential to maximizing the service life of a built-up roofing system. Windward Roofing provides comprehensive maintenance programs that include semi-annual inspections, documentation of roof conditions, and prompt attention to any issues identified during inspections. Our maintenance services for BUR systems include clearing debris from the roof surface and drainage components, inspecting and resealing flashings and termination points, checking for blisters, ridges, or splits in the membrane, evaluating aggregate coverage and redistributing gravel as needed, and documenting roof conditions for asset management and budgeting purposes.

Proactive maintenance catches minor issues before they develop into major problems. A small blister addressed during a routine inspection costs a fraction of what a full-scale repair would require if the blister were allowed to grow and eventually rupture. Our maintenance programs are designed to protect your investment and extend the operational life of your BUR system.

BUR Tear-Off and Replacement

When a built-up roof reaches the end of its service life or has sustained damage beyond the point of cost-effective repair, Windward Roofing provides complete tear-off and replacement services. Our experienced crews safely remove existing BUR materials, including multiple layers of felt, bitumen, and aggregate, down to the structural deck. All materials are disposed of in compliance with local regulations and environmental standards.

Following tear-off, we inspect the roof deck for damage and make any necessary repairs before installing the new roofing system. Building owners replacing a BUR system can choose to install a new BUR assembly or transition to a different roofing technology such as TPO, EPDM, or modified bitumen depending on their performance requirements and budget. Our team provides expert guidance on the best replacement option for each building's unique circumstances.

Why Choose Windward Roofing for BUR?

Windward Roofing and Construction has been installing, maintaining, and replacing built-up roofing systems since 1984. Our crews have decades of hands-on experience with BUR construction techniques and understand the critical details that determine the long-term performance of these systems. We work with premium materials from manufacturers including Johns Manville, Tremco, and GAF, and we follow industry best practices established by the National Roofing Contractors Association.

Our project portfolio spans hundreds of BUR installations and replacements across Illinois, Wisconsin, Michigan, Indiana, and Florida. Whether you need a new BUR installation, expert maintenance for an existing system, or a complete tear-off and replacement, Windward Roofing delivers the quality craftsmanship and professional service your building deserves. Contact us today to schedule a roof inspection and receive a detailed estimate for your BUR roofing project.

Frequently Asked Questions About Built-Up Roofing