What is a Built-up Roof?
Built-up roofing—commonly referred to as BUR—has been a reliable solution for low-slope commercial roofs for more than a century. This time-tested system is composed of alternating layers of bitumen (asphalt) and reinforcing felts made from fiberglass or polyester. The assembly is then topped with a protective surface layer, which may include gravel, stone, mineral granules, or a smooth, reflective coating, depending on the building’s needs and environmental conditions.
The multi-ply construction of a BUR system offers exceptional durability and long-term performance. Its layered design provides built-in redundancy, enhancing resistance to water intrusion and strengthening the overall integrity of the roof—making it especially well-suited for demanding commercial environments.
Why Choose BUR Roofing?
While roofing technologies have advanced over the years, the built-up roof (BUR) remains a trusted choice among architects, contractors, and facility managers. Its long-standing reputation for reliability across diverse climates and demanding conditions is a testament to its proven performance. For commercial buildings that require durable, cost-effective protection against the elements, BUR remains a practical solution that has truly stood the test of time.
As one of the most widely used commercial roofing systems, BUR offers a host of benefits that make it a top contender for low-slope applications:
- Durable: The multi-layer construction enhances resistance to wear and tear, making BUR ideal for high-traffic rooftops and harsh environments.
- Long-Lasting: With proper installation and maintenance, a BUR roof can last 20 years or more.
- Low Maintenance: Once installed, BUR systems require minimal upkeep, reducing long-term operational costs.
- Moisture Resistant: The redundant layering creates a watertight seal, offering excellent protection against leaks.
- Fire and Weather Resistant: BUR systems perform well in a variety of weather conditions and can be formulated to provide fire resistance for added safety.
Whether you're looking to repair, restore, or replace a commercial roof, BUR systems offer a time-tested solution that balances performance, longevity, and value.
Components of a Built-Up Roof
A BUR system is composed of several key components:
- Base Sheets: These are the initial layers applied directly to the roof deck. They provide a foundation for the subsequent layers. The base sheet is crucial as it acts as a primary barrier against moisture, ensuring that the structural deck remains dry and free from water damage.
- Interply Sheets: These are reinforcing fabrics, often made of fiberglass or organic materials, laid between layers of bitumen to add strength and stability. The interply sheets are strategically placed to distribute weight evenly and prevent the bitumen from cracking under stress.
- Bitumen: This is the adhesive material used to bond the layers together. It can be applied hot or cold, depending on the specific system being used. Bitumen serves as the core waterproofing agent in a BUR system, creating a seamless barrier that repels water infiltration.
- Surfacing: The top layer is usually composed of gravel or a reflective coating. This provides UV protection and enhances the roof's durability. The surfacing not only protects the underlying materials from weathering but also contributes to energy efficiency by reflecting solar radiation.
How Is a Built-Up Roof Installed?
Installing a built-up roofing (BUR) system is a multi-step process that requires precision, expertise, and careful execution to ensure a durable, weather-resistant finish. Each phase of installation plays a vital role in the overall performance of the roof. When done correctly, a BUR system offers superior protection and minimizes the risk of leaks, structural damage, or premature failure.
Preparation
The first step in the installation process is thorough preparation of the roof deck. This involves cleaning the surface of all debris, dust, and contaminants, as well as conducting a detailed inspection to identify any existing damage or weaknesses. It’s critical that the deck is structurally sound and capable of supporting the additional weight of the built-up layers. Any necessary repairs should be completed prior to installation to avoid issues down the line. A clean, solid foundation ensures proper adhesion and long-term integrity of the roofing system.
Layering Process
- Base Layer: The first step is to apply the base sheet directly to the roof deck. This layer acts as a barrier against moisture. It is essential that the base layer is installed smoothly and without wrinkles to ensure a proper seal.
- Bitumen Application: Once the base sheet is in place, a layer of bitumen is applied to form the foundation of the waterproofing system. This can be accomplished using hot-mopped asphalt, cold-applied adhesives, or modified bitumen, depending on the project's specifications and environmental conditions. The chosen application method plays a critical role in ensuring proper adhesion, performance, and longevity of the roofing system.
- Reinforcing Fabric: A layer of reinforcing fabric is embedded into the bitumen. This process is repeated multiple times to build up the necessary number of layers. Each layer must be carefully aligned and bonded to avoid any weak points in the system.
- Surfacing: Finally, a top layer of gravel or a protective coating is applied. This protects the underlying layers and adds weight to help hold the roofing system in place. The surfacing layer also enhances the aesthetic appeal of the roof, providing a finished look.
Considerations for Built-Up Roofs
While built-up roofs offer numerous benefits, there are also some considerations to keep in mind. Being aware of these factors ensures that building owners and contractors can make fully informed decisions. Addressing these considerations upfront can help mitigate potential challenges during and after installation.
Weight
Built-up roofing systems are relatively heavy compared to other commercial roofing options, due to their multi-layered construction. Before installation, it’s essential to verify that the building’s structure can safely support the added load. Consulting with a structural engineer can help determine whether reinforcements or modifications are needed.
The additional weight of a BUR system can influence the building’s overall structural dynamics, making it a key factor to address during the planning phase. Proper load assessment not only ensures safety but also helps prevent long-term structural issues and supports the roof’s performance over time.
Installation Time
Installing a built-up roof can be a time-intensive process, especially on large commercial buildings. Each layer must be methodically applied and properly set before the next is added, which naturally extends the overall timeline. As a result, careful planning and coordination are essential—particularly for projects with tight construction schedules.
However, this deliberate approach is critical to ensuring the roof’s durability and long-term performance. While the installation may take longer than some single-ply systems, the added time is an investment in a proven, resilient roofing solution.
Odor and Fumes
The use of hot bitumen can produce strong odors and fumes during installation, which may be a concern for some building occupants. Adequate ventilation and safety precautions should be taken to minimize exposure. Contractors should communicate with building occupants about the installation process to manage expectations.
While modern techniques and materials have reduced the impact of odors and fumes, it remains a consideration for indoor air quality during installation. Understanding these factors can help in planning for temporary accommodations or adjustments during the installation phase.
Get Us On Your Roof Today
National Roofing Partners brings decades of experience and nationwide coverage to every BUR project. Contact us to learn more about how built-up roofing can protect your facility for the long haul.