Built Up Hot Mopped Roof

What Is a Built-Up Hot Mopped Roof?

A Built-Up Hot Mopped Roof (BUR) is a traditional roofing system commonly used on flat or low-slope roofs. It consists of multiple layers of roofing felt or fabric alternated with hot-applied bitumen, creating a durable, waterproof membrane. This method has been widely adopted in commercial and industrial buildings due to its long-lasting protection against weather elements and fire resistance.

Materials Used in a Built-Up Hot Mopped Roof System

The primary materials involved in constructing a BUR roof include:

• Roofing Felt or Fabric: Usually fiberglass or organic felt that provides the structure for the roof membrane.
• Bitumen (Asphalt or Coal Tar): Hot-applied adhesive substance that bonds each layer to form a waterproof barrier.
• Surfacing Materials: Gravel, mineral granules, or reflective coatings protect the bitumen from UV degradation and mechanical damage.

The number of plies (layers) typically ranges from three to five, balanced between adequate waterproofing and flexibility.

Installation Process of a Hot Mopped Built-Up Roof

The BUR installation involves a sequential layering technique that ensures seamless waterproofing through hot bitumen application.

1. Preparation: The roof deck is inspected and cleaned to ensure a proper bonding surface.
2. Primer Application: Sometimes a base primer is applied to enhance adhesion.
3. First Layer of Bitumen: Hot asphalt or coal tar is mopped directly onto the deck.
4. Embedding Felt: The first layer of roofing felt is pressed into the hot bitumen.
5. Subsequent Layers: Steps 3 and 4 are repeated 2-4 times depending on design requirements.
6. Surfacing: The final bitumen layer is topped with gravel or mineral granules to protect from UV rays and mechanical wear.

Proper temperature control during the hot mopping process is essential to achieve a uniform and durable membrane without damage to the materials.

Benefits of a Built-Up Hot Mopped Roof

Durability and Longevity: BUR systems can last 15 to 30 years with proper maintenance, providing excellent protection against extreme weather.

Waterproofing and Seamless Coverage: The hot mopping process creates a continuous, watertight membrane that minimizes leaks common in other roofing types.

Fire Resistance: With the coal tar bitumen option, BUR provides enhanced resistance to fire compared to many other roofing membranes.

Energy Efficiency: Reflective surfacing options such as mineral granules can improve energy efficiency by reducing heat absorption and cooling costs.

Cost-Effectiveness: Initial installation costs are moderate, with low long-term repair costs due to the system’s robustness.

Common Applications of Built-Up Hot Mopped Roofs

BUR roofing is especially favored in sectors requiring reliable flat or low-slope roofing solutions:

• Commercial Buildings: Warehouses, retail stores, and office buildings often use BUR to ensure long-term waterproofing.
• Industrial Facilities: Manufacturing plants prefer BUR for its resistance to chemicals and physical damage.
• Multi-family Residential: Apartment buildings with flat roof designs utilize BUR systems for ease of maintenance and durability.

Its adaptability also allows for use in many climates, from humid coastal areas to dry, hot regions.

Maintenance and Inspection of Built-Up Hot Mopped Roofs

Regular maintenance extends a BUR roof’s lifespan. Key maintenance tips include:

• Periodic Inspections: At least twice a year and after severe weather events to detect cracks, ponding water, or loose gravel.
• Cleaning Debris: Remove leaves, dirt, and debris to avoid blocked drainage and accelerated wear.
• Addressing Repairs Promptly: Small cracks or blisters should be repaired immediately to prevent moisture infiltration.
• Gravel Replenishment: When necessary, add ballast gravel or protective coatings to enhance UV resistance.

Scheduled professional assessments ensure timely detection of potential problems before costly damage occurs.

Comparing Built-Up Hot Mopped Roofs to Other Roofing Systems

Choosing the best roofing system depends on factors such as building type, budget, climate, and maintenance capacity.

Environmental Impact and Sustainability

BUR roofing has environmental considerations due to the use of petroleum-based bitumen. However, many manufacturers now offer recycled and low-VOC bitumen products to reduce emissions during installation.

Additionally, BUR roofs with reflective surfaces contribute to reducing urban heat island effects by reflecting sunlight and lowering roof surface temperatures.

Recycling old BUR membrane materials is more challenging than some modern single-ply systems, but advances in roofing technology are addressing sustainability concerns.

Cost Factors Influencing Built-Up Hot Mopped Roof Installation

Several elements impact the overall cost of installing a BUR system, including:

• Roof Size and Complexity: Larger and irregularly shaped roofs require more materials and labor.
• Material Quality: The choice between asphalt and coal tar, number of plies, and surfacing type affect pricing.
• Labor Costs: Skilled roofing contractors are needed due to the specialized hot mopping process.
• Existing Roof Condition: Tear-off or preparation of underlying materials can add to expenses.

Despite relatively moderate upfront costs, BUR roofs deliver long-term value through durability and low maintenance.

Safety Considerations During Installation

The hot mopping process involves heating bitumen to high temperatures, which poses hazards:

• Burn Risks: Contact with hot bitumen can cause severe burns, so workers require protective gear and training.
• Fumes: Bitumen vapors may be harmful; adequate ventilation and respiratory protection are essential.
• Fire Hazards: Bitumen is flammable; strict fire safety protocols must be followed on job sites.

Employing certified and experienced roofing professionals ensures a safer installation with compliance to OSHA regulations.