What Is a Built-Up Composition Roof (BUR)?
Built-Up Composition Roofs (BUR) are one of the oldest and most reliable flat roofing systems in the United States. Known for their durability and waterproof qualities, BUR systems consist of multiple layers of materials that form a solid, protective barrier on low-slope roofs. These roofs are commonly found on commercial buildings, warehouses, and some residential structures, offering long-lasting performance against weather and wear.
To grasp the core components and benefits of BUR roofs, the following table summarizes their key elements:
| Component | Description |
|---|---|
| Base Layers | Multiple plies of asphalt-saturated felt or fiberglass mats |
| Asphalt or Bitumen | Hot or cold applied asphalt sheets layered between plies for waterproofing |
| Surfacing | Gravel, mineral granules, or reflective coatings added on top for UV protection |
| Installation Method | Layering (built-up) system with hot tar, cold adhesive, or asphalt layers |
| Roof Slope Compatibility | Best suited for flat or low-slope applications (typically less than 3:12 pitch) |
Core Components and Materials of Built-Up Composition Roofs
The BUR system is essentially a layering technique that provides robust protection by combining multiple plies of roofing felt with asphalt or bitumen. These layers create redundancy, improving waterproofing and puncture resistance.
Roofing Felts or Felt Ply
Roofing felts are made from natural or fiberglass mats saturated with asphalt. The felts provide the structural base that asphalt is bonded to, ensuring mechanical strength.
Asphalt or Bitumen Layers
Typically applied hot, these layers act as adhesive and waterproofing agents. They are instrumental in sealing the layers together and protecting the building interior from water infiltration.
Surfacing Material
The top layer commonly consists of crushed stone (aggregate), smooth mineral granules, or reflective coatings. The aggregates protect the asphalt from UV radiation and mechanical damage, extending the roofing lifespan.
Installation Process of Built-Up Composition Roofs
The installation of BUR roofing is a meticulous process. It involves:
- Preparation: Cleaning and smoothing the roof deck surface for optimal adhesion.
- Applying Base Layers: Sequentially laying down felt plies impregnated with hot asphalt or cold adhesive.
- Building up Layers: Repeated layering of asphalt and felt creates the “built-up” system, typically with three to four plies.
- Adding Surfacing: Final aggregate or coating applied while the last bitumen layer is still warm to ensure a strong bond.
This method results in a thick, sealed membrane that provides excellent waterproofing and durability on flat roofs.
Advantages of Built-Up Composition Roofs
BUR roofs offer several benefits that make them an attractive choice for commercial and industrial roofing projects.
- Durability: The multiple layers provide resistance to wear, punctures, and weather damage.
- Waterproofing Efficiency: Hot asphalt layers form a continuous barrier against water intrusion.
- Fire Resistance: Asphalt is naturally fire retardant, enhancing building safety.
- Cost-Effectiveness: Though materials and installation can be labor-intensive, BUR roofs have a long service life reducing maintenance costs.
- Low Maintenance: With proper installation, BUR roofs require minimal upkeep.
- Thermal Performance: The thick layers can offer insulation benefits, stabilizing indoor temperatures.
Common Applications and Ideal Uses
Built-Up Composition Roofs are best suited for buildings with low to no slope roofs, such as:
- Commercial office buildings and retail centers
- Industrial warehouses and manufacturing plants
- Educational institutions and hospitals
- Some residential apartment buildings with flat roof designs
They excel in urban and industrial environments where durability and water resistance are high priorities under constant exposure to weather elements.
Maintenance and Longevity of BUR Roofs
When properly installed and maintained, BUR roofs can last from 20 to 30 years or longer. Routine maintenance includes:
- Regular inspections for cracks, blisters, or splits
- Cleaning debris and ensuring adequate drainage
- Repairing damaged gravel or mineral surfacing to prevent UV cracking
- Sealing any punctures or seam failures promptly
Preventative care significantly extends the roof’s service life and avoids costly repairs.
Potential Drawbacks and Considerations
Despite its advantages, BUR roofing has some limitations:
- Installation Complexity: Requires skilled labor and safety precautions due to hot asphalt use.
- Weight: BUR roofs are heavy, necessitating a structurally sound deck.
- Limited Slope Use: Not suitable for steeply pitched roofs.
- Initial Cost: High upfront material and labor expenses compared to some membrane roofing options.
- Environmental Concerns: Hot asphalt and gravel layers are less sustainable than newer roofing technologies.
BUR Roof Vs. Other Flat Roofing Systems
| Feature | Built-Up Roof (BUR) | Modified Bitumen | Single-Ply Membrane |
|---|---|---|---|
| Layers | Multiple (>3) layers of felt and bitumen | 2-3 layers with modifiers for flexibility | Single synthetic sheet (EPDM, TPO, PVC) |
| Durability | High | Moderate to High | Moderate |
| Installation | Hot asphalt, labor-intensive | Torch-applied or cold adhesive | Mechanically fastened or adhered |
| Maintenance | Low if maintained well | Moderate | Low to Moderate |
| Lifespan | 20-30 years | 15-20 years | 10-20 years |
| Cost | Moderate to High | Moderate | Low to Moderate |
Environmental and Energy Considerations for BUR Roofing
With rising focus on sustainability, BUR roofing systems can be modified with reflective coatings to reduce energy consumption by lowering roof surface temperatures. However, the materials traditionally used—such as asphalt and aggregate—have environmental footprints. Modern adaptations include:
- Using recycled asphalt or felt materials
- Installing reflective or “cool roof” coatings
- Incorporating insulation layers underneath BUR to enhance energy efficiency
These improvements help align BUR roofs with green building standards and reduce operational costs.