Gravel Built-Up Roof on an Industrial Roof Surface

A built-up roof (BUR), also known as a tar and gravel roof, is a type of roofing system that has been used for many decades, primarily in commercial and industrial buildings. A BUR roof is a multi-layered roofing system designed to provide durability, waterproofing, and insulation.

The construction of a built-up roof involves applying multiple layers of roofing felts or mats. These felts are typically made of organic or fiberglass materials and are saturated with sticky, viscous petroleum-derived bitumen. The BUR roofing felts are alternated with hot-applied or cold bitumen layers, creating a cohesive and robust roofing membrane.

In addition to the bitumen and roofing felts, a built-up roof often includes a surfacing layer. Traditionally, this surfacing layer consists of gravel or crushed stone, which serves as a protective barrier and helps to reflect sunlight. The gravel or stone also provides additional weight and stability to the roof system. However, alternative surfacing options, such as reflective coatings or modified bitumen membranes, are also used to enhance energy efficiency and meet specific design requirements.

Types of Built-Up Roofs: Gravel BUR vs. Smooth BUR

  • Surface Appearance: The most apparent difference is the surface appearance. Gravel BUR has a layer of gravel on top, which provides a textured, rugged appearance. On the other hand, Smooth BUR has a sleek and even surface without gravel.
  • UV Protection: Gravel BUR offers better protection against sun ultraviolet (UV) radiation. The layer of gravel acts as a shield, reducing the direct exposure of the underlying roofing materials to UV rays. Smooth BUR, lacking the gravel layer, may require additional UV protection through coatings or reflective materials.
  • Cooling Efficiency: Gravel BUR tends to absorb and retain more heat due to the dark-colored gravel. This can increase the building's cooling load, especially in warmer climates. With its reflective surface options, Smooth BUR can help reflect sunlight and reduce heat absorption, enhancing cooling efficiency.
  • Maintenance: Gravel BUR may require more maintenance due to loose gravel. Periodic inspections ensure the gravel is evenly distributed, prevent ponding, and address potential gravel displacement or drainage issues. Smooth BUR generally requires less maintenance, although it may require regular inspections and occasional repairs.
  • Durability: Both gravel BUR and smooth BUR can offer durable roofing systems. The multiple layers of bitumen and reinforcing materials provide strength and resistance to weathering, foot traffic, and punctures. However, the presence of gravel in gravel BUR can add an extra layer of protection against physical damage.
  • Weight: Gravel BUR is heavier due to the added weight of the gravel layer. This increased weight may require additional structural considerations during installation or if the roof is being retrofitted. Smooth BUR, without the gravel layer, is relatively lighter.

Have a built-up roof in need of attention? Click here to find an American WeatherStar Approved Contractor near you.

Advantages of a Built-Up Roof

Durability

Built-up roofs are known for their exceptional durability. They are constructed with multiple layers of bitumen, typically asphalt, and reinforced with roofing felt or fiberglass layers. This layered approach creates a robust and resilient roofing system that can withstand the elements, including heavy rains, wind, and UV radiation. Built-up roofs have a long life expectancy, often lasting 20 to 30 years or more with proper maintenance.

Waterproofing

The multiple layers of bitumen and roofing felts in a built-up roof provide excellent waterproofing capabilities. The layers’ redundancy helps minimize the risk of leaks and ensures that water does not penetrate the roof’s surface making BUR roofs suitable for areas with high rainfall or where water ponding may occur.

Thermal Performance

The multiple layers in a built-up roof also contribute to its thermal performance. The layers of insulation, typically placed between the bitumen layers, provide thermal resistance, helping to regulate the building’s internal temperature and reduce energy consumption for heating and cooling, which can lead to energy savings and improved comfort for building occupants.

Fire Resistance

Built-up roofs are known for their fire-resistant properties. The bitumen and roofing layers create a barrier that helps prevent the spread of fire. This can be particularly advantageous in commercial and industrial settings where fire safety is a primary concern.

Click here to learn more about the 4 Commercial Roof Fire Ratings.

Easy Maintenance and Repair

Built-up roofs are relatively easy to maintain and repair. Regular maintenance, such as clearing debris and inspecting for damage, can help extend the roof’s lifespan and prevent minor issues from turning into significant problems. In the event of damage or leaks, repairs can be made by adding additional layers of bitumen and roofing felt, allowing for targeted and localized fixes.

Disadvantages of a Built-Up Roof

Weight

One of the significant disadvantages of a built-up roof is its weight. The multiple layers of bitumen and roofing felts, along with the gravel or stone ballast used to protect the roof, make it a heavy roofing system. This weight may require additional structural support to ensure the building can handle the load. Assessing the building’s structural capacity before installing a built-up roof is crucial.

Installation Complexity

The installation of BUR is more complex and time-consuming compared to some other roofing systems. It involves the careful application of multiple layers of bitumen and roofing felts, as well as the incorporation of insulation and the final protective layer of gravel or stones. This complexity requires skilled and experienced roofing contractors to ensure proper installation.

Potential for Leaks

Although built-up roofs are known for their waterproofing capabilities, there is still a potential for leaks, especially if the installation is not done correctly or the roof is not adequately maintained. Over time, the roofing can degrade, and the seams between the layers can become susceptible to water infiltration. Regular inspections and maintenance are essential to address any potential issues promptly.

Limited Design Flexibility

Built-up roofs are not known for their design flexibility. The traditional tar and gravel appearance may not suit the aesthetic preferences of some building owners or architects. However, alternatives such as reflective coatings or modified bitumen membranes can provide some design options while maintaining the benefits of a BUR roof.

Odor and Fumes

While installing a built-up roof, odors and fumes can be emitted from the hot bitumen and other materials used. This can concern buildings where occupants may be sensitive to smells or have respiratory issues. Adequate ventilation during installation is necessary to mitigate this concern.

Environmental Impact

The use of asphalt in built-up roofs raises environmental concerns due to its carbon footprint and non-renewable nature. Asphalt production requires significant energy consumption and contributes to greenhouse gas emissions. Additionally, the removal and disposal of built-up roofs at the end of their lifespan can pose challenges regarding waste management and recycling.

Built-Up Roofs: Frequently Asked Questions

A well-installed and well-maintained built-up roof can last anywhere from 20 to 30 years or even longer.

On average, the cost of a built-up roof installation can range from $3 to $7 per square foot. However, this is a rough estimate and the actual cost can fall outside this range.

As a general guideline, it is recommended to have a professional inspection of a built-up roof at least once a year. However, in some instances, more frequent inspections may be necessary, varying on several factors, including the age of the roof, local weather conditions, and any specific requirements or recommendations from the roofing manufacturer.

Click here to learn more.

Yes! Built-up roofs are perfect candidates for elastomeric coating systems. At the same time, a professional roofing contractor should evaluate factors such as the existing roof’s condition, the extent of damage, and compatibility with the coating system.

To learn more about the benefits of roof restoration, check out this post: Roof Restoration: The Comprehensive Guide

Conclusion

Overall, a built-up roof is a durable, time-tested roofing system that provides reliable waterproofing, insulation, and fire resistance. Its multi-layered construction and protective surfacing make it a popular choice for flat or low-sloped roofs in commercial and industrial settings.

When considering a built-up roof, it is essential to evaluate the specific needs of the building, structural considerations, budget constraints, and desired aesthetics. To learn more about the advantages and disadvantages of Built-Up Roofs, click here to speak with a customer service representative.