Built Up Roof Material: A Comprehensive Guide to BUR Roofing

Built up roof material, commonly referred to as BUR, combines multiple layers of asphalt or coal tar with reinforcing fabrics to create a durable, weatherproof roofing system. This article explores BUR components, varieties of cap sheets, installation considerations, performance in different climates, maintenance, and how to choose the right BUR system for a project. By understanding the strengths and tradeoffs of built up roofs, property owners and builders can optimize longevity, energy efficiency, and cost-effectiveness.

What Is Built Up Roof Material

Built up roof material is a multilayer roofing system designed to provide waterproof protection for flat and low-slope roofs. It typically comprises alternating plies of reinforcing fabrics and bitumen, topped by a protective cap sheet. The result is a seamless, durable surface that resists UV exposure, foot traffic, and weathering. BUR systems are valued for their long track record in commercial and industrial buildings and their ability to be customized for various climates and budgets.

Key Components Of BUR Roofing

Plies And Reinforcement

BUR systems use multiple plies, usually made from fiberglass or organic felts, embedded in hot asphalt or coal tar pitch. The number of plies varies by specification and intended performance, typically ranging from three to five or more. The reinforcing fabric adds strength and tear resistance while distributing loads across the roof surface.

Bitumen Layer

The bitumen acts as the adhesive binder between plies. It may be hot-applied asphalt, coal tar, or a self-adhering membrane in modern configurations. Bitumen provides waterproofing and resilience to temperature changes when properly installed.

Cap Sheet

The top layer, or cap sheet, protects the BUR from UV exposure and physical damage. Cap sheets can be smooth or granule-surfaced and may include reflective or mineral-reinforced options for enhanced durability and energy performance.

Protective Surfacing

Granular surfacing, mineral granules, or reflective coatings reduce UV degradation and improve long-term performance. The protective layer also contributes to skid resistance and weathering resistance at the roof edge and parapets.

Types Of BUR Cap Sheets

Cap sheets vary based on material composition and performance attributes. Common options include:

• Granulated Cap Sheets: Mineral granules protect the surface and provide durability.
• Smooth Cap Sheets: A sleek surface that can be coated or painted for reflective properties.
• Reflective Cap Sheets: Light-colored granules or coatings designed to reduce heat absorption and improve energy efficiency.
• Self-Adhering Cap Sheets: Peel-and-stick options simplify installation and reduce hot asphalt handling.

Advantages And Disadvantages

Understanding the tradeoffs helps determine suitability for a project. Advantages include proven waterproofing performance, good life expectancy with proper maintenance, and flexibility in repair and retrofit options. Disadvantages involve longer installation times, heavier roof loads, and the need for skilled workmanship to ensure even compaction and heat application during installation. In regions with extreme heat, care must be taken to manage asphalt temperatures to avoid accelerated aging.

Applications And Climate Considerations

BUR systems are well-suited for commercial flat roofs, warehouses, and institutional buildings. In hot, sunny climates, reflective cap sheets and proper insulation reduce cooling loads. In cold climates, BUR performs well against freeze-thaw cycles when installed with appropriate vapour barriers and insulation. For roof decks with limited slope, BUR’s layered construction provides robust waterproofing and redundancy against leaks.

Installation Essentials

Proper BUR installation hinges on surface preparation, heat application, and ventilation. Key steps include:

• Inspecting and repairing the substrate to ensure a clean, dry base.
• Applying a suitable vapour barrier and insulation as required by local codes.
• Sequentially laying plies with consistent heating and adhesion to prevent air pockets.
• Installing the final cap sheet with appropriate detailing around penetrations, edges, and terminations.
• Providing edge protection and parapet detailing to prevent wind uplift and wind-driven moisture.

Maintenance And Lifespan

Routine maintenance extends BUR life. Regular inspections identify lifted edges, wrinkles, or worn cap sheets. Addressing blisters, cracks, or membrane damage promptly reduces the risk of leaks. Cleaning debris, inspecting flashings, and resealing edges help preserve waterproofing. Typical BUR systems offer 20 to 40 years of service, depending on materials, climate, and maintenance intensity. A professional roof assessment every 3 to 5 years is advisable for aging systems.

Cost Considerations

Cost drivers include the number of plies, surface cap sheet type, insulation needs, and local labor rates. While BUR can have higher initial costs than some single-ply membranes, its durability and repairability often yield favorable long-term value. Regional material availability and the complexity of penetrations influence price. Energy performance upgrades, such as reflective or cooling coatings, can reduce operating costs over time.

Environmental And Sustainability Aspects

BUR systems can contribute to building efficiency through reflective roofs and proper insulation. Some manufacturers offer asphalt with recycled content, and VOC emissions are a consideration during installation. Proper waste management and encapsulation of asphalt during application support environmental goals. Selecting a BUR system with recyclable cap sheets and long service life aligns with sustainable construction practices.

Choosing A Contractor And Best Practices

Expert installation is critical for BUR performance. When selecting a contractor, consider:

• Experience with BUR systems and local climate conditions.
• References and documented projects similar in scope.
• Detailed written specifications, warranty terms, and post-installation support.
• Safety programs and adherence to building codes and fire regulations.

Frequently Asked Questions

Q: How does BUR compare to single-ply membranes? A: BUR offers redundancy and durability with multiple plies, but single-ply membranes can install faster and may require less weight. Choice depends on climate, budget, and maintenance plans.

Q: Is BUR fire-rated? A: BUR can be fire-rated when properly designed and installed, with appropriate cap sheets and substrates meeting code requirements.

Q: Can BUR be retrofitted on existing roofs? A: Yes, BUR can be installed over existing roofs when the structure supports the added weight and proper substrate preparation is performed.

Infographic And Quick Reference

Visuals can illustrate BUR layers, typical ply counts, and maintenance timelines. A compact table below summarizes common BUR configurations:

Built up roof material remains a robust choice for flat or low-slope roofs in the United States. By selecting appropriate plies, cap sheets, and protective surfacing, along with professional installation and routine maintenance, BUR systems can deliver dependable waterproofing, structural compatibility, and long-term value for diverse building types.