Built Up Roof (BUR) systems are a long-standing choice for commercial and industrial buildings in the United States. They combine multiple plies of reinforcing fabric and bitumen to deliver durable waterproofing, storm resistance, and seasonal performance. This guide examines the main BUR materials, their advantages, installation considerations, and how to choose the right combination for a given building and climate.
Overview Of Built Up Roof Systems
BUR roofing is a multi-layer membrane that creates a durable waterproof barrier. Traditional BUR uses alternating layers of bitumen and reinforcing felts, topped with a protective finish such as gravel or a reflective coating. Over time, newer variants like modified bitumen offer improved performance in a single-ply or semi-ballasted format. Understanding the material family helps building owners compare cost, durability, and maintenance needs.
Core Components And Materials
Key elements in BUR systems include the reinforcing plies, the bitumen, the weathering surface, and the ballast or membrane finish. The reinforcing plies are typically fiberglass or organic felts. Bitumen can be asphalt or coal tar pitch, with asphalt favored for modern applications due to lower odor and easier handling. The finish protects the membrane from UV exposure and weathering, while ballast such as gravel or a reflective coating provides weight, security, and solar reflectivity.
Common Materials Used In BUR Roofing
Reinforcing Plies: Fiberglass or organic felts provide tensile strength. Fiberglass is more resistant to shrinkage and offers consistent performance in modern BUR installations.
Bitumen: Traditional asphalt is widely used in new BUR installations for its workability and cost. Coal tar pitch, though less common today, remains in older systems and can offer excellent waterproofing but requires odor mitigation and careful handling.
Surface Finish: Gravel ballast is the classic option, protecting the membrane from UV damage and adding weight to resist wind uplift. Modern BUR systems may use reflective cap sheets or mineral granules to reduce heat absorption and improve energy efficiency.
Modified Bitumen Variants In The BUR Family
Modified bitumen (MB) membranes blend asphalt with polymers to enhance performance. APP (Atactic Polypropylene) and SBS (Styrene-Butadiene-Styrene) are common modifiers. These products can be surfaced with mineral granules or asphaltic coatings and installed using heat-wusion, self-adhesive, or cold-applied methods. MB systems often provide fewer plies than traditional BUR but deliver improved flexibility, wind uplift resistance, and ease of installation.
Installation Methods And Best Practices
BUR installation combines heat application, cold-applied methods, and mechanical fastening depending on the system. Key steps include surface preparation, primer application, layering of plies with asphalt or coal tar pitch, and final surface finishing. Proper tackiness, seam integrity, and curing time are essential for long-term waterproofing. When gravel ballasting is used, weight distribution and ballast depth must meet manufacturer and local code requirements to prevent wind uplift and drainage issues.
Durability, Longevity, And Maintenance
BUR roofs typically offer 20 to 40 years of service, depending on climate, workmanship, and maintenance. They perform well in heavy rainfall and snow zones when properly installed. Regular maintenance includes inspecting for blisters, ridges, or exposed plies, repairing damaged ballast, and ensuring proper drainage to prevent ponding. In regions with extreme heat, reflective coatings can extend life and reduce cooling loads. Periodic resealing and re-sealing of seams help maintain waterproof integrity.
Environmental And Energy Considerations
BUR systems can be engineered to improve energy efficiency with reflective or green coatings, reducing heat transfer into the building. Recycled-content felts and properly managed coal tar components can impact environmental profiles. In new constructions or major retrofits, selecting low-odor asphalt or MB variants can improve worker safety and indoor air quality during installation. Proper maintenance minimizes emissions associated with leaks or structural failures.
Cost Considerations And Lifecycle Economics
Initial costs for BUR roofing include materials, labor, and ballast. Traditional asphalt-based BUR tends to have favorable upfront pricing, while MB systems may have higher material costs but offer quicker installation and better long-term performance. Lifecycle costs should account for expected maintenance, energy savings from reflective surfaces, and the potential need for periodic gravel replacement or overlay. A professional assessment helps align a BUR choice with budget and expected building performance.
Choosing The Right BUR Materials For A Building
- Climate Assessment: Consider thermal load, wind exposure, and precipitation when selecting bitumen and surface finish.
- Building Use: Heavier ballast or reflective finishes may be preferred for roof accessibility and energy performance.
- Maintenance Capability: Regular inspection capabilities influence whether a traditional BUR or MB system is best.
- Environmental Goals: Opt for low-odor materials and reflective coatings to improve sustainability.
- Local Codes And Warranties: Ensure compatibility with code requirements and manufacturer warranties for your region.
Maintenance Tips To Extend BUR Performance
- Schedule periodic inspections after severe weather to detect blisters, cracks, or exposed plies.
- Check ballast stability and prevent soil or debris accumulation that can cause drainage issues.
- Monitor roof edges and penetrations for wear; reseal joints and flashing as needed.
- Maintain proper roof drainage to avoid standing water and accelerated wear.
Common Pitfalls And How To Avoid Them
- Underestimating roof slope and drainage can lead to ponding; ensure design accounts for water flow.
- Inadequate ballast or improper ballast placement can lead to wind uplift and failure.
- Incompatible materials or improper adhesion reduces waterproofing; follow manufacturer guidelines strictly.
- Poor ventilation during installation can cause odors or curing issues; ensure site meets safety standards.