Built Up Roof (BUR) systems have long been a trusted choice for commercial and industrial roofing due to their durability and proven performance. These multi-layered roofing systems provide excellent protection against harsh weather and UV exposure while offering reliable waterproofing. This article explores the construction, materials, benefits, installation processes, and maintenance of built up roof systems to provide a thorough understanding suitable for building owners, contractors, and roofing professionals.
| Aspect | Details |
|---|---|
| Construction | Multiple layers of bitumen and reinforcing fabrics |
| Materials | Asphalt or coal tar pitch, fiberglass or felt felts |
| Benefits | Highly durable, waterproof, UV resistant, fire resistant |
| Common Uses | Commercial, industrial rooftops, flat or low-slope structures |
| Maintenance | Regular inspection, repairing blisters/cracks, cleaning surface |
What Is a Built Up Roof System?
A Built Up Roof (BUR) system is a traditional flat or low-slope roofing method characterized by multiple layers of waterproofing materials. Originating in the early 1900s, BUR remains popular due to its strong waterproofing capabilities. The system is composed of alternating layers of bitumen—which may be asphalt or coal tar pitch—and reinforcing fabrics, usually fiberglass or organic felts. These layers are laminated together to form a thick, dense roofing membrane.
Often called a “tar and gravel roof” because of the typical aggregate surface, a BUR’s components create a multi-ply barrier that effectively protects roofing substrates from thermal cycling, water intrusion, and mechanical damage.
Materials Used in Built Up Roof Systems
Understanding the materials is key to appreciating the BUR’s durability. The core components include:
- Bitumen: Acts as the waterproofing agent. Two main types are used – asphalt and coal tar pitch. Asphalt provides flexibility and adheres well to substrates. Coal tar pitch is highly resistant to chemical degradation and has excellent waterproofing qualities.
- Felts or Reinforcing Fabrics: Made from fiberglass or organic fibers, these materials reinforce the bitumen layers, adding tensile strength and reducing the risk of cracking or tearing under stress.
- Surfacing Materials: To protect the constructed roof membrane, surfacing is applied. This can be gravel, mineral granules, or reflective coatings such as aluminum. The surfacing safeguards the bitumen from UV rays and mechanical damage.
Design and Construction of Built Up Roofs
The construction sequence of a BUR system typically involves:
- Deck Preparation: The substrate (usually concrete, plywood, or metal) must be clean, dry, and structurally sound.
- Base Sheet Installation: A base sheet is mechanically fastened or adhered to the deck surface to provide a stable foundation.
- Layering Felts and Bitumen: Several plies of felt saturated with hot bitumen are alternated and layered. The typical BUR has between three to five plies.
- Surfacing Application: The final layer is covered with aggregate like gravel or reflective coatings to protect the membrane.
Heat application is critical during installation to ensure proper adhesion and waterproofing, typically by hot asphalt or asbestos-free coal tar pitch.
Advantages of Built Up Roofing Systems
BUR systems offer multiple benefits, making them a preferred roofing solution for commercial buildings:
- Exceptional Waterproofing: The multiple bitumen and fabric layers create a redundant, waterproof barrier against leaks.
- Durability: BUR roofs last 20 to 30 years or more, with superior resistance to weather, foot traffic, and mechanical stress.
- Thermal Protection: The thick membrane also provides good insulation, reducing building energy costs.
- Fire Resistance: Coal tar-based BUR systems have strong fire resistance, which is critical in industrial settings.
- Low Maintenance: Minimal upkeep is required when installed properly; regular inspections help prolong service life.
Common Applications of Built Up Roof Systems
BUR is especially suitable for:
- Commercial Buildings: Office buildings, retail complexes, and warehouses commonly use BUR for flat roofs.
- Industrial Facilities: Factories and manufacturing plants benefit from BUR’s fire resistance and durability.
- Schools and Hospitals: Facilities requiring reliable, long-lasting roofs to protect sensitive environments.
- Low-Slope Roofs: Ideal for any flat or low-slope surface where water drainage is slow, providing excellent waterproofing.
Installation Process and Best Practices
Optimal BUR installation requires skilled labor and attention to safety:
- Surface Preparation: The roof deck must be smooth, clean, and free from debris to ensure proper adhesion.
- Weather Conditions: Installation is best done in dry, warm conditions to ensure bitumen heats and adheres correctly.
- Multiple Layers: Plies should be evenly applied without wrinkles or folds to prevent weak points.
- Proper Surfacing: Adequately cover the membrane with gravel or reflective coating to shield from UV, weather, and fire hazards.
Routine safety measures must be followed given the use of hot bitumen and open flames during installation.
Maintenance and Repair Recommendations
Maintaining a BUR system is crucial for extending its lifespan and performance:
- Regular Inspections: Schedule bi-annual roof checks to identify blisters, cracks, or soft spots.
- Cleaning Debris: Remove leaves, gravel displacement, and dirt that can trap moisture and degrade the membrane.
- Prompt Repairs: Seal cracks or punctures quickly using compatible bitumen patches or roofing cement to prevent leaks.
- Restore Surfacing: Replace lost gravel or reapply reflective coatings to maintain UV and fire resistance.
Comparing Built Up Roof Systems with Other Roofing Types
| Feature | Built Up Roof (BUR) | Modified Bitumen | Single-Ply Membranes |
|---|---|---|---|
| Durability | High (20-30 years) | Moderate to High | Moderate (15-20 years) |
| Installation | Hot application, labor-intensive | Heat-welded or self-adhered | Mechanically fastened or adhered |
| Waterproofing | Multi-layer redundancy | Good waterproofing layer | Single membrane |
| Maintenance | Low with proper care | Moderate | Requires regular inspection |
| Cost | Moderate to High upfront | Moderate | Lower upfront cost |
The choice of roofing system depends on budget, building design, and maintenance preferences.
Environmental Considerations of Built Up Roof Systems
Modern BUR systems are increasingly designed to be environmentally friendly:
- Recycled Materials: Some felts and gravel surfacing use recycled content, reducing landfill waste.
- Energy Efficiency: Reflective coatings reduce heat absorption, lowering cooling costs and reducing urban heat island effect.
- Longevity: Long service life reduces material consumption over time compared to short-lived roofing.
New innovations also include cold-applied bitumen alternatives which limit harmful fumes during installation.