Built Up Roofing Definition for Flat Roofs and Commercial Buildings

Built up roofing, often abbreviated as BUR, is a traditional roofing system that combines multiple layers of aggregate, asphalt, and reinforcing fabrics to create a durable, weatherproof membrane. This method has been used for decades on flat and low-slope roofs in commercial, industrial, and some residential settings. The system relies on the cumulative strength of several plies and a protective top layer to resist water intrusion, UV exposure, and temperature fluctuations. Understanding BUR helps property owners weigh durability, maintenance needs, and long-term costs.

What Is Built Up Roofing (BUR) Exactly

Built up roofing is a multi-ply membrane constructed by alternately layering bitumen and reinforcing felts, capped with a protective surface. The typical arrangement may include 3 to 5 plies of reinforcing felt, each coated with hot or cold asphalt, followed by a gravel or granulated cap sheet. The asphalt provides waterproofing, while the reinforcement adds tensile strength. The final layer shields the roof from weather and provides a reflectivity or texture depending on the surface chosen.

How Built Up Roofing Works

BUR forms a weatherproof barrier through its layered construction. The bitumen layers seal gaps and resist water infiltration, while multiple plies distribute structural loads and thermal stress. The top surface, either gravel, mineral granules, or reflective cap sheets, protects the membrane from UV degradation and mechanical damage. In hot climates, reflective cap sheets can improve energy efficiency by reducing heat absorption. When installed correctly, BUR can offer decades of service with periodic maintenance.

Key Materials Used In BUR Systems

The core components are: reinforcing felts (asphalt-impregnated fiberglass or organic felts), asphalt or coal tar pitch (as the waterproofing binder), and a top cap sheet (gravel, aggregate, or mineral granules). The combination yields a resilient, watertight membrane. Some modern BUR systems use polyester or fiberglass mats for higher tear resistance. Roof decks commonly require proper drainage, deck preparation, and edge detailing to ensure long-term performance.

Advantages Of Built Up Roofing

Durability and puncture resistance come from multiple plies and a robust cap sheet. Waterproofing is enhanced by the layered design, reducing punctures from foot traffic or equipment. BUR performs well under temperature variations and is relatively resistant to wind uplift when properly installed. The gravel or granule surface provides additional protection against UV rays and physical damage, extending the roof’s life.

Limitations And Considerations

BUR can be heavier than newer roofing systems, requiring structural assessment to avoid overload. Installation requires skilled labor and precise hot-mop techniques, which can affect upfront costs. Maintenance involves inspecting edges, flashings, and penetrations for leaks, as well as periodic surface cleaning. In some climates, the gravel surface may shed over time, necessitating resurfacing or cap sheet replacement. Environmental concerns may arise from asphalt emissions during installation, so contractors may implement ventilation and control measures.

Applications And Suitability

Commercial buildings with flat or low-slope roofs are ideal BUR candidates due to its long track record and proven waterproofing. Industrial facilities, institutions, and high-traffic roofs benefit from BUR’s durability. While less common than single-ply membranes on new construction, BUR remains prevalent in retrofit projects where a proven, repairable system is valued. The choice often depends on climate, expected roof life, maintenance access, and local code requirements.

Maintenance, Lifespan, And Repairs

Typical BUR lifespans range from 15 to 30 years, depending on traffic, climate, and maintenance. Regular inspections should target edge details, penetrations, and gravel cap integrity. Patching can address localized breaches, but extensive failures may require re-roofing or complete BUR removal. Preventive measures include cleaning debris, evaluating drainage, and ensuring proper ventilation. When leaks appear, timely diagnosis avoids extensive interior damage and reduces repair costs.

Choosing The Right Contractor

Selecting a qualified contractor is critical for BUR success. Look for proven BUR experience, proper licensing, and current insurance. Ask for project references and a detailed work plan covering surface preparation, plies, asphalt type, cap sheet selection, drainage considerations, and warranty terms. Ensure the crew uses appropriate safety practices and adheres to local building codes and fire regulations. A clear written agreement helps manage expectations and minimizes disputes.

Cost Considerations And Value

Initial BUR installation costs reflect material quality, ply count, and surface finish. While BUR can have higher upfront costs than some modern membranes, its long service life and repairability can yield favorable total cost of ownership. Energy efficiency options, such as reflective cap sheets, may reduce cooling costs. Owners should weigh up-front expenses against expected lifespan, maintenance needs, and the potential for extended warranties.

Frequently Asked Questions

• Is BUR waterproof? Yes, BUR is designed to be waterproof through its multi-ply construction and asphalt sealants, though proper installation is essential.
• What maintenance does BUR require? Regular inspections of edges, flashings, penetrations, and cap sheet integrity, plus debris removal and drainage checks.
• How long does BUR last? Typical lifespans range 15–30 years with proper care and climate-appropriate design.
• How does BUR compare to single-pply membranes? BUR offers superior durability and puncture resistance in many cases, but may require more maintenance and heavier installation than modern single-ply systems.