Built Up Roofing Definition and Essentials
Built up roofing (BUR) is a traditional, durable roofing system used on many commercial and industrial buildings in the United States. This article explains the definition, construction, advantages, limitations, and best practices for installation, maintenance, and longevity. It also compares BUR to other common roofing types to help property owners and managers make informed decisions.
Definition And Core Concept
Built up roofing is a multilayer system composed of alternating layers of bitumen and reinforcing sheets, topped with a protective surface layer. The typical assembly includes a vapor barrier, reinforcing sheets such as felts or fiberglass, hot asphalt or coal tar pitch as the bitumen, and a final top coat that can be gravel, gravel and membrane, or a reflective coating. The name “built up” reflects the accumulation of multiple plies to create a weatherproof barrier with robust waterproofing capabilities.
How It’s Constructed
A BUR installation starts with a roof deck and a continuous vapor barrier to control moisture. Next, alternating plies of roofing felt or reinforced sheets are embedded in hot asphalt, coal tar, or an elastomeric adhesive. Each ply adds strength and waterproofing, and a final protective layer—such as mineral granules, ballast, or a reflective cap sheet—shields the system from UV exposure and environmental wear. The exact number of plies varies by climate, roof slope, and building code requirements, typically ranging from three to five plies for most commercial applications.
Key Benefits
- Durability: BUR is renowned for long service life under harsh weather conditions, including wind, hail, and temperature fluctuations.
- Waterproof Integrity: Multiple plies create a resilient barrier against leaks and bulk water intrusion.
- Thermal Performance: When paired with reflective surfaces or insulation, BUR can contribute to energy efficiency.
- Cost-Effectiveness Over Time: Though installation costs can be higher upfront, long-term maintenance and durability can reduce life-cycle costs.
- Versatility: Suitable for flat or low-slope roofs commonly found on commercial buildings.
Potential Drawbacks
- Installation Temperature Sensitivity: Hot application requires temperate conditions; extreme heat or cold can affect workmanship.
- Weight: The ballast and multiple plies add weight, which may impact structural considerations on older buildings.
- Maintenance Needs: Regular inspection of seams, penetrations, and ballast is essential to prevent leaks.
- Environmental Concerns: Some asphalt-based components involve materials with environmental considerations, though modern BUR products are designed with safer formulations.
Common Materials Used
- Bitumen: Hot asphalt or coal tar pitch served as the adhesive and waterproofing medium.
- Reinforcing Sheets: Mineral-felt felts or fiberglass felts provide strength and puncture resistance.
- Top Surface: Gravel ballast, mineral-surfaced cap sheets, or reflective coatings protect the system from UV and weathering.
- Adhesives: Some modern BUR installations use cold-applied or self-adhering asphaltic membranes for ease of application.
Applications And Suitability
BUR is widely used on commercial flat or low-slope roofs, including office buildings, schools, warehouses, and retail complexes. It performs well in urban environments with freeze-thaw cycles and is compatible with various insulation schemes. Its resilience makes it a preferred choice where long service life and proven waterproofing are priorities. For reroofing projects, BUR can be installed over existing decks when the underlying structure is sound and compatible with ballast and top coatings.
Maintenance And Inspection
Regular inspections—at least twice yearly and after major weather events—are essential. Look for signs of:
- Blisters, splits, or punctures in the roofing felt
- Loose or displaced ballast or cap sheets
- Standing water indicating drainage issues
- Leaks around penetrations such as vents, skylights, or HVAC curbs
Maintenance actions may include resealing seams, replacing damaged plies, reballasting, or applying a fresh top coat. Proper drainage, air leakage control, and timely repairs extend BUR life and prevent costly water damage.
Installation Considerations And Best Practices
- Climate And Temperature: Choose construction and bitumen type appropriate for local climate and seasonal temperature ranges.
- Deck Condition: Ensure the substrate is clean, dry, and structurally sound before application.
- Ventilation And Vapor Control: Adequate vapor barriers help prevent condensation-related issues in insulation layers.
- Professional Installation: BUR requires skilled labor for proper heating, ply alignment, and compaction of ballast.
- Safety: Follow OSHA guidelines for heating operations, hot asphalt handling, and fall protection during installation.
Comparisons With Other Roofing Systems
Compared to single-ply membranes like TPO or EPDM, BUR offers superior durability and a time-tested waterproof history, especially under heavy weather exposure. In energy performance, reflective BUR or granule surfaces can help reduce cooling loads, while modern single-ply systems may offer lighter weight and faster installation. For heritage or long-term reliability, BUR remains a robust option, though newer materials continue to evolve in performance and environmental impact.
Common Misconceptions
- BUR Is Always Heavy: Weight varies with the number of plies and ballast; engineered designs manage load.
- BUR Cannot Be Repaired: Localized repairs to plies and seams are common and cost-effective when addressed promptly.
- All BUR Systems Require Gravel: Modern systems can use alternative top surfaces, including reflective or membrane caps, depending on project goals.
Safety, Codes, And Environmental Considerations
Building codes govern BUR installation standards, fire ratings, and wind uplift requirements. Environmental considerations include proper handling of asphalt and tar products and responsible disposal of removed materials. Contractors should follow industry guidelines and manufacturer instructions to ensure safety, code compliance, and optimal system performance.
Frequently Asked Questions
- What does BUR stand for? Built Up Roofing, a multilayer bitumen-based roofing system.
- How many plies are typical in BUR? Most installations use three to five plies, depending on climate and performance requirements.
- Is BUR suitable for flat roofs? Yes, BUR is specifically designed for flat or low-slope roofs.
- Can BUR be repaired? Yes, localized repairs to plies and seams are common and extend roof life.