Built up roofing, commonly known as BUR, is a traditional multi-layer roofing system designed for durability and weather resistance. It combines asphalt, coal tar, or other felts with reinforcing fabrics to create a sealed, waterproof surface. BUR is widely used on flat or low-slope roofs in the United States due to its proven track record, long service life, and ability to withstand extreme temperature variations. Understanding its definition, components, and installation methods helps building owners evaluate whether BUR fits their needs and climate.
What Is Built Up Roofing
Built up roofing is a composite system assembled from multiple plies, or layers, of roofing felt and waterproofing asphalt or coal tar. The layers are sealed with asphalt or bitumen and finished with a protective cap sheet, ballast, or granules. The design creates a durable, weather-resistant surface that can handle ponding water on flat roofs. BUR systems are known for redundancy: if one ply is damaged, other plies continue to provide waterproofing, reducing the risk of leaks over time.
How Built Up Roofing Works
The core principle of BUR is layering. Each ply adds strength and impermeability, while the waterproofing agents fill microcracks to prevent water intrusion. A typical BUR assembly includes a substrate, multiple plies of felts bonded with hot or cold adhesive, a waterproofing layer, and a surface finish such as gravel, cap sheet, or reflective coating. The final surface protects the underlying membrane from UV radiation, physical damage, and weathering, extending roof life considerably.
Common Materials In BUR Systems
Key components include roofing felts (cotton, fiberglass, or organic), hot asphalt or coal tar, a base sheet, and a cap sheet. Some systems use self-adhering sheets or cold-adhesion methods. Surface finishes vary by climate and aesthetic goals; common options are gravel ballast, polymer-modified bitumen sheets, or reflective coatings. The choice of materials affects durability, ease of maintenance, and energy efficiency, with reflective surfaces improving curb appeal and reducing cooling costs.
Types Of Built Up Roofing Systems
BUR systems come in several configurations. A conventional BUR uses hot-applied asphalt to bond plies, followed by a cap sheet and ballast. A modified BUR integrates flexible asphalt modifiers to improve elasticity and crack resistance. Self-adhesion BUR uses pre-primed felts bonded with pressure-sensitive adhesives, reducing fire risk during installation. Each type offers trade-offs in installation speed, odor, VOC emissions, and long-term performance, so selection depends on project conditions and local codes.
Benefits And Drawbacks
Benefits include excellent waterproofing, proven longevity, and good resistance to hail and wind uplift when properly installed. BUR can accommodate building movement, and ballast protects the roof surface from UV damage. It also provides a strong, low-slope solution compatible with existing substrates. Drawbacks involve heavier weight, higher installation costs, and potential odor during hot asphalt application. Regular maintenance is required to prevent seam degradation and ballast displacement.
Installation Overview And Best Practices
Professional BUR installation begins with substrate preparation: cleaning, leveling, and ensuring proper deck drainage. Plies are installed with hot or cold adhesives, or self-adhering methods, followed by a cap sheet. In colder climates, hot asphalt may require ventilation and safety measures due to fumes. Best practices emphasize fire safety, accurate ply sequencing, and proper ballast placement. Seams and penetrations must be carefully sealed, and insulation should be compatible with the BUR system to maintain thermal performance.
Maintenance And Repairs
Maintenance focuses on inspecting for blisters, lifted edges, and membrane cracks. Patches or ply repairs should follow manufacturer guidelines to restore waterproofing. Periodic cleaning of ballast and debris prevents drainage obstructions. After severe storms, a professional inspection can identify hidden damage under ballast. Concrete or metal roof decks should be checked for corrosion or delamination. Timely repairs extend system life and prevent costly full-replacement scenarios.
Environmental Considerations
BUR can contribute to energy efficiency when paired with reflective cap sheets or cool-roof coatings, reducing heat absorption in hot climates. Some manufacturers offer recycled content felts and reduced-emission bitumen options. Proper disposal of old BUR materials aligns with local regulations, and many projects can pursue LEED or green building credits by selecting sustainable components and reflective surfaces.
Choosing A Roofing Contractor
Selecting a qualified contractor is essential for BUR performance. Look for licensure, insurance, and relevant experience on flat or low-slope roofs. Request references and check the contractor’s adherence to local building codes and safety standards. Ask about project warranties, inspection schedules, and the availability of manufacturer-approved materials. A detailed written plan should outline substrate preparation, ply sequence, adhesive type, ballast specification, and finish details.
Frequently Asked Questions
What is the difference between BUR and modified bitumen? BUR uses multiple plies of felt with asphalt, while modified bitumen adds polymer modifiers for enhanced elasticity. Is BUR suitable for sloped roofs? BUR is designed for flat or low-slope roofs and may not perform well on steep pitches without specialized detailing. How long does BUR typically last? Depending on climate and maintenance, BUR can last 20 to 40 years or longer with proper care.