What is a Built-Up Roof in Construction in Canada?

In the realm of roofing systems, the built-up roof (BUR) holds a prominent place, especially in commercial and industrial construction. The durability, cost-effectiveness, and time-tested performance of BUR systems make them a popular choice for a wide range of building types across Canada. Whether you are a contractor, architect, or building owner, understanding the nuances of a built-up roofing system is crucial for making informed decisions on your roofing project.

What is a Built-Up Roof (BUR)?

A built-up roof (BUR) is a type of flat roofing system constructed by layering multiple materials to create a durable, water-resistant surface. The BUR system is composed of multiple layers of bitumen (typically asphalt or coal tar) and reinforcing materials such as roofing felt or fiberglass matting. This layered structure creates a highly robust roofing system known for its waterproofing, longevity, and resilience under harsh weather conditions.

The process of creating a BUR is referred to as “built-up” because it involves constructing the roof incrementally in layers, with each layer adding additional protection and strength. While BUR roofs have been around for decades, their ability to withstand the extreme weather conditions in Canada, including heavy snow, ice, and strong winds, makes them a highly reliable option for commercial buildings.

Components of a Built-Up Roof (BUR)

A typical BUR system is made up of several key components that work together to provide a long-lasting and effective roofing solution. These components include:

1. Base Sheet

The base sheet is the first layer of the BUR system. It is typically made of a fiberglass mat or organic felt material, providing the foundational surface upon which subsequent layers are built. The base sheet is usually mechanically fastened or adhered to the roof deck and serves as the foundation for the rest of the roofing system.

2. Reinforcing Fabric or Felt Layers

The second component of a BUR system is the reinforcing fabric or roofing felt. This layer is typically composed of materials like asphalt-saturated felt or fiberglass that provide additional structural strength and reinforcement to the roofing system. The fabric or felt is embedded in hot bitumen or cold adhesive, helping to bond the layers together.

Multiple layers of reinforcing felt may be added, depending on the desired thickness and strength of the roof. These layers increase the roof’s resistance to water infiltration, physical damage, and UV degradation.

3. Bitumen Layers (Asphalt or Coal Tar)

Bitumen is the adhesive that holds the layers of the BUR together and provides waterproofing. The most common types of bitumen used in BUR systems are asphalt and coal tar. Asphalt is the most widely used material, while coal tar is preferred in areas where chemical resistance is important, such as in industrial environments.

Asphalt or coal tar is applied in hot liquid form, which is then spread across the felt or reinforcing fabric to create a strong bond. This bitumen layer plays a critical role in sealing the roof, preventing water infiltration, and enhancing the overall waterproofing of the system.

4. Cap Sheet or Gravel Layer

The cap sheet is the top layer of a built-up roof system, designed to provide additional protection and durability. This layer is typically made of modified bitumen (MB) or smooth-surfaced material such as asphalt. In some cases, a gravel ballast may be used instead of a cap sheet. The gravel serves as an additional protective layer and helps shield the roof from ultraviolet (UV) rays, physical damage, and debris.

The cap sheet or gravel ballast also acts as a barrier to the elements, protecting the underlying layers from weather-related wear and tear. The inclusion of a gravel layer is common in Canada, where heavy snow and ice can put additional stress on roofing systems.

Advantages of Built-Up Roofing (BUR) in Canada

The built-up roof system offers a variety of advantages that make it a top choice for commercial and industrial roofing in Canada. These benefits include:

1. Durability and Longevity

A well-constructed BUR system is known for its exceptional durability, often lasting 20-30 years or longer when maintained properly. The multiple layers of bitumen, felt, and reinforcing fabric create a robust and long-lasting roofing system that can withstand harsh weather conditions, including freezing temperatures, heavy snow, and strong winds that are common in many parts of Canada.

2. Excellent Waterproofing

One of the primary reasons that BUR roofs are highly regarded is their superior waterproofing capabilities. The multiple layers of bitumen and felt create a continuous barrier that prevents water infiltration. The use of bituminous materials ensures that the roof remains impervious to water, reducing the risk of leaks, mold, and water damage to the building’s interior.

3. Energy Efficiency

Another significant advantage of BUR roofs is their ability to contribute to energy efficiency. The layered construction of the system provides thermal resistance, which helps to keep the building cool during the summer and warm in the winter. This can result in lower heating and cooling costs over the life of the building. Additionally, the top layer of the BUR system can be modified to reflect sunlight, further improving the roof’s energy efficiency.

4. Fire Resistance

BUR systems are highly resistant to fire due to the non-combustible properties of the asphalt and coal tar materials. This feature makes BUR an excellent choice for buildings that require additional fire protection, such as commercial and industrial properties.

5. Low Maintenance

Once a BUR roof is installed, it generally requires minimal maintenance. Periodic inspections and routine cleaning are typically sufficient to maintain the roof’s performance. When compared to other roofing systems, BUR roofs are known for their low-maintenance nature, making them a cost-effective option in the long term.

Disadvantages of Built-Up Roofing (BUR)

While the built-up roof offers numerous benefits, it also comes with a few drawbacks to consider:

1. Heavy Weight

One of the main disadvantages of a BUR roof is its weight. The multiple layers of materials, including bitumen, felt, and gravel, can make the roof system quite heavy. As a result, additional structural support may be required, especially for older buildings or those with a weaker foundation. This can increase the cost of installation and the complexity of the roofing project.

2. Installation Complexity

The process of installing a BUR system is more labor-intensive than some other roofing systems, requiring skilled labor and specialized equipment. The hot application of bitumen can also pose safety hazards if not properly managed. While BUR roofs are long-lasting and durable, their installation requires significant expertise to ensure that the layers are properly adhered, and the roofing system is correctly aligned.

3. Potential for Odor and Fumes

The application of hot bitumen during the installation process can release unpleasant odors and fumes, which may be problematic in some environments. Proper ventilation and safety precautions must be followed during installation to minimize any risks associated with the use of hot materials.

Conclusion

A built-up roof (BUR) system is a reliable, durable, and cost-effective solution for commercial and industrial roofing in Canada. With its ability to withstand extreme weather conditions, superior waterproofing, fire resistance, and energy efficiency, BUR remains a highly regarded roofing choice for various types of buildings. While there are certain considerations regarding the weight and complexity of installation, the long-term benefits of a BUR system far outweigh these challenges.

To ensure a successful installation, it is crucial to work with experienced roofing contractors who are knowledgeable about BUR systems and Canadian construction standards. By understanding the components, benefits, and potential drawbacks of BUR roofing, property owners can make well-informed decisions that will protect their building for years to come.

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