Built up felt roofing, often referred to as BUR, combines multiple layers of asphalt-saturated felt with a protective surface, delivering a strong, weather-resistant roof. This method has a long track record in the United States, particularly for flat and low-slope roofs. Understanding its composition, installation, benefits, and maintenance can help homeowners evaluate whether BUR fits their building needs and budget.
What Is Built Up Felt Roofing
Built up felt roofing is a traditional roofing system that creates a layered assembly to resist water intrusion. A typical BUR assembly includes alternating plies of reinforcing felt and bitumen, topped with a protective surface such as gravel, mineral granules, or a reflective coating. The number of plies can vary, commonly ranging from three to five, depending on climate and roof design. The outer cap sheet provides UV protection and weather resistance, while the inner plies offer strength and flexibility.
In the United States, BUR is favored for its proven performance on commercial flat roofs and some residential low-slope configurations. Modern compositions use modified bitumen or asphalt blends to improve elasticity in cold weather while maintaining long-term waterproofing. The result is a dense, durable roof that can resist wind uplift, temperature fluctuations, and minor structural movement.
How It Is Installed
Installation begins with a clean, dry substrate and proper insulation. An asphalt or coal tar pitch is heated and spread as an adhesive or a self-adhesive membrane is laid down. Felt plies are then embedded into the hot or cold adhesive, or adhered with bitumen, with each ply carefully rolled and sealed to prevent air pockets. The process continues layer by layer until the desired number of plies is achieved. The final surface treatment—gravel ballast, mineral granules, or a reflective coating—protects against UV exposure and weathering.
Key factors that influence performance include substrate preparation, proper ply alignment, and thorough sealing at joints, penetrations, and drains. Skilled installation is essential to prevent leaks and to ensure long-term durability. In some markets, torch-down or cold-applied methods are used for additional adherence, though these require specific safety protocols and handling procedures.
Advantages Of Built Up Felt Roofing
- Proven Waterproofing: The layered construction creates multiple barriers against water ingress, increasing resilience to ponding water on low-slope surfaces.
- Durability In Cold Climates: BUR systems tolerate temperature cycling and have a long service life when properly installed.
- Flexibility And Impact Resistance: The plies absorb minor structural movement and resist hail impacts when properly designed.
- Cost-Effectiveness Over Time: Initial costs are moderate, and a long service life can reduce replacement frequency.
- Repairability: Damaged plies can sometimes be repaired or spot-repaired without full membrane removal.
Disadvantages And Considerations
- Weight And Structural Load: BUR systems are heavier than single-ply membranes, which may require structural assessment.
- Labor Intensity: Installation is labor-intensive, making workmanship a critical factor in performance.
- Aesthetics: The traditional BUR appearance may not suit all architectural styles; gravel caps can also trap debris.
- Maintenance Needs: Regular inspections are essential to detect seam aging, flashing weaknesses, and surface wear.
Maintenance And Longevity
Maintenance for built up felt roofing focuses on periodic inspections, cleaning, and prompt repair of any leaks or blisters. Regularly check for cracks in the cap sheet, compromised granules, lifted seams, and clogged drains. Gravel ballast should be cleared from gutters and downspouts to prevent ponding and accelerated wear. In regions with strong UV exposure or frequent hail, surface coatings may require refreshment or re-ballasting over time.
Indicative lifespans for BUR systems vary with climate, maintenance, and installation quality, but many installations endure 20 to 40 years. Recoating or reballasting at mid-life can extend service life. Timely repairs after windstorms or hail can prevent more expensive structural damage later.
Costs And Budgeting
Cost factors include roof size, the number of plies, substrate condition, insulation needs, and labor rates. In the United States, BUR installation typically ranges from $5 to $11 per square foot, depending on local market conditions and the complexity of detailing. Gravel ballast adds some weight and cost, while lift equipment and safety measures contribute to total expenses. Long-term budgeting should consider maintenance, potential re-coating, and the expected lifespan of the system.
When evaluating bids, homeowners should ask for: a detailed scope of work, the number of plies, surface finish, warranty terms (materials and workmanship), and the contractor’s experience with BUR installations on residential or low-slope roofs.
Environmental Considerations
BUR systems involve asphalt-based materials, which can raise concerns about environmental impact. Recycled asphalt and energy-efficient surface finishes are increasingly used to reduce heat absorption and heat island effects. A reflective or granule surface can improve roof reflectivity, helping lower cooling loads in hot climates. Proper disposal and recycling of old roofing materials at end of life are important components of responsible project planning.
Choosing A Contractor
Selecting a qualified contractor is crucial for BUR success. Look for licensed professionals with documented experience on similar roof types and proven safety records. Request references, inspect completed projects, and verify insurance coverage. Ensure the bid includes: substrate preparation details, ply count, surface finish, warranty coverage, and a clear schedule. A site visit to assess current roof conditions helps tailor the plan and prevent expensive surprises during installation.
BUR Versus Alternatives
Compared to single-ply membranes (EPDM, TPO) and metal roofs, BUR offers robust waterproofing and durable performance on low-slope surfaces but may incur higher labor costs and heavier loads. For coastal or storm-prone regions, BUR’s multi-layer design provides a reliable barrier against wind-driven rain, while modern modified bitumen options offer enhanced elasticity. Homeowners should weigh installation complexity, maintenance needs, and local climate when choosing between BUR and alternatives.
Maintenance Schedule And Quick Checks
- Biannual inspections, especially after severe weather
- Check for blisters, cracks, or visible wear in the cap sheet
- Inspect flashing around penetrations, skylights, and vents
- Ensure gutters and drains are clear to prevent standing water
- Document issues with photos and address quickly with a contractor
Built up felt roofing remains a durable, time-tested option for flat and low-slope roofs in the United States. With proper installation, routine maintenance, and thoughtful material choices, BUR can deliver long-term waterproofing, weather resilience, and value for homeowners seeking a reliable roofing solution.