Built Up Felt Roofing: A Comprehensive Guide to Durability and Performance

Built up felt roofing, also known as BUR, is a long-standing option for flat and low-slope roofs. This guide explains what BUR is, how it’s constructed, the benefits and potential drawbacks, installation considerations, maintenance, and common issues. It highlights practical insights for homeowners, contractors, and facility managers seeking reliable roofing that balances cost, longevity, and performance in diverse American climates.

What Is Built Up Felt Roofing

Built up felt roofing is a multilayer system engineered to create a durable, weatherproof surface. It typically combines alternating layers of reinforcing felts (felt sheets) and bitumen binders (asphalt or coal tar pitch) with a final protective surface layer. The resulting membrane offers robust waterproofing, enhanced fire resistance, and the ability to shed standing water on flat or low-slope roofs. In modern applications, gravel surfacing or reflective coating may be applied to the top layer to extend life and improve energy efficiency.

Layers And Materials

Traditional BUR assemblies follow a layered approach that progressively builds waterproofing and protection. A typical configuration includes:

• Insulation or substrate: Plywood, gypsum, or rigid foam boards provide a stable base.
• Primer: A bonding layer that improves adhesion between substrates and felts.
• Bitumen adhesive: Hot or cold application to bind the felt layers.
• Reinforcing felts: Layers of asphalt-impregnated felt or fiberglass/asphalt felt that add strength and tear resistance.
• Additional bitumen coats: Each felt layer is sealed with a coating to create a seamless interface.
• Surface reinforcement: Either mineral granules, gravel, or a reflective cap sheet to protect the top surface from UV exposure and weathering.

Common materials include:

• Asphalt BUR: The traditional option using asphalt-saturated felts.
• Coal tar BUR: Historically used for aggressive chemical environments; less common today due to odor and health concerns.
• Fiberglass or organic felts: Modern reinforcement options that improve tear resistance.

Benefits Of Built Up Felt Roofing

BUR offers several advantages that make it a preferred choice for many flat roofs in the United States. Key benefits include:

• Durable waterproofing: Multiple layers create a redundant barrier against leaks.
• Versatility: Performs well on low-slope surfaces and can accommodate various substrate types.
• Fire resistance: When properly installed, BUR provides enhanced fire protection, especially with mineral surface coverings.
• Repairability: Localized repairs can extend the system’s life without complete replacement.
• Proven performance: A long track record in commercial and institutional buildings across diverse climates.

Installation Considerations

Proper installation is critical for BUR performance and longevity. Important considerations include:

• Surface preparation: The substrate must be clean, dry, and structurally sound to ensure adhesion and prevent moisture entrapment.
• Ventilation and drainage: Adequate roof slope and drainage reduce ponding, which can accelerate wear.
• Hot asphalt handling: Safety measures are essential during the application, including temperature controls and proper equipment.
• Layer sequencing: Correct order of felts and coatings prevents delamination and ensures watertightness.
• Top surface choice: Gravel, mineral granules, or reflective coatings influence UV protection, foot traffic, and energy performance.

Maintenance And Lifespan

The lifespan of built up felt roofing varies by climate, workmanship, and maintenance. In general, BUR roofs can last 15 to 30 years with proper care. Maintenance practices include:

• Periodic inspections: Check for cracks, blisters, ponding, and surface damage after extreme weather.
• Clean drainage paths: Remove debris from gutters and scuppers to prevent water buildup.
• Prompt repairs: Address exposed or damaged areas early to prevent leaks from propagating.
• UV protection: Ensure the top surface remains protected by gravel or reflective coating to minimize aging.

Common Issues And Repairs

BUR systems, while robust, can encounter specific problems over time. Typical issues include:

• Blisters or air pockets: Occur when moisture is trapped or heat causes expansion; usually repairable by removing affected sections and resealing.
• Cracking or splitting: Result of temperature fluctuations or membrane aging; localized patching or panel replacement may be needed.
• Delamination: Layers separate due to poor adhesion or substrate movement; requires professional re-bonding or re-lamination.
• Foot traffic wear: High-traffic areas can wear down top layers; protective surfacing helps mitigate.

Environmental And Energy Considerations

Environmental factors influence BUR performance and operating costs. Key considerations include:

• UV exposure: The top surface must be protected to prevent rapid aging; gravel or reflective coatings reduce heat absorption.
• Thermal performance: BUR can contribute to roof heat gain or loss, depending on surface finish; reflective caps improve energy efficiency in hot climates.
• recycled materials: Some modern BUR systems incorporate recycled asphalt or fibers, contributing to sustainability goals.
• VOC emissions: Bituminous materials may release volatile organic compounds during installation; proper ventilation and curing are important.

Comparisons With Alternatives

When selecting a roofing system for flat or low-slope structures, ongoing considerations include cost, durability, and maintenance. Built up felt roofing compares with several alternatives:

• EPDM: A single-ply membrane known for ease of installation and flexibility; generally lower maintenance but may require more frequent seam care.
• TPO and PVC: Reflective single-ply options with strong energy efficiency and heat resistance; often more expensive upfront but lower long-term maintenance in some climates.
• Modified bitumen: A modern evolution of BUR, combining polymer-modified bitumen with reinforcement for improved performance and easier installation.
• Metal roofing: Durable and long-lasting with low maintenance; can be more costly and specific to building design.

Selecting A Contractor And Ensuring Quality

Choosing a qualified contractor is essential for BUR performance. Consider these steps:

• References and credentials: Check experience with BUR systems and verify licenses and insurance.
• Detailed written proposal: Require a full scope, materials list, warranty terms, and maintenance plan.
• Warranty coverage: Understand asphalt, felt, and top-surface warranties, and what triggers coverage.
• Quality installation practices: Look for proper substrate prep, heat management for asphalt, and appropriate top-surface protection.

Top Practical Takeaways

Built up felt roofing remains a resilient option for low-slope roofs in the United States. Its layered design provides robust waterproofing, fire resistance, and repairability. Proper preparation, correct layering, and timely maintenance are critical to maximizing lifespan and performance. For facilities seeking a durable, proven system with a long track record, BUR offers a compelling blend of protection, adaptability, and cost-effectiveness when installed by skilled professionals.