What Is Built-Up Roofing in Construction? A Comprehensive Guide

Built-up roofing (BUR) is a widely used roofing system in construction, particularly for commercial and industrial buildings. Known for its durability and versatility, BUR provides a long-lasting solution for flat or low-slope roofs. This system has been a staple in the roofing industry for decades due to its effectiveness in waterproofing, insulating, and protecting buildings from various environmental factors.

In this article, we will explore everything you need to know about built-up roofing in construction. We will cover its definition, components, installation process, benefits, and considerations for maintenance. This guide aims to provide a thorough understanding of BUR, helping you make informed decisions about its use in your construction projects.

What Is Built-Up Roofing (BUR)?

Built-up roofing, often referred to as tar and gravel roofing, is a type of roofing system made up of multiple layers of bitumen (usually asphalt or coal tar) and reinforcing materials such as fiberglass or felt. These layers are applied in a specific sequence to create a durable, weather-resistant barrier for a roof surface.

BUR systems are commonly used on flat or low-slope roofs due to their ability to provide excellent water resistance. The construction of BUR typically consists of a base sheet, several layers of felt, and bitumen. Once these layers are applied, a final layer of gravel or a reflective coating is added for additional protection and aesthetic appeal.

Components of Built-Up Roofing (BUR)

A standard built-up roofing system typically includes the following key components:

1. Base Sheet: The first layer of the BUR system, the base sheet, is typically made of asphalt-saturated felt or fiberglass. It provides the foundation for the subsequent layers and helps with the adhesion of the bitumen.
2. Reinforcing Layers: These layers consist of felt or fiberglass matting, which serves to reinforce the roofing system. Felt is made from asphalt-soaked fiberglass or organic material, while fiberglass mats provide additional strength and durability.
3. Bitumen: Bitumen is the sticky, waterproof substance used to bond the layers together. It is typically made of asphalt or coal tar and is applied in multiple layers between the reinforcing materials.
4. Top Layer: The top layer of BUR often consists of gravel, which acts as a protective barrier against UV rays, physical damage, and the elements. Alternatively, some systems may use reflective coatings to improve energy efficiency and protect against UV degradation.
5. Gravel or Aggregate: The final layer is usually a gravel ballast that helps hold the roofing materials in place. Gravel also adds weight to the roof, preventing wind uplift, and acts as a protection against ultraviolet (UV) radiation.

How Built-Up Roofing Is Installed

The installation of built-up roofing is a detailed and meticulous process. It requires skilled professionals to ensure proper layering, adhesion, and protection. Below is an overview of the typical installation process:

1. Preparation of Roof Surface: Before applying the built-up roofing system, the roof surface must be cleaned and prepared. This includes removing any debris, old roofing materials, and ensuring that the surface is smooth and dry.
2. Application of Base Sheet: The first step in the BUR installation is the application of the base sheet. The base sheet is unrolled across the roof and adhered to the substrate using hot asphalt or cold adhesive.
3. Layering of Felt and Bitumen: After the base sheet is secured, the process of layering begins. Felt is applied on top of the base sheet, and bitumen is used to bond the layers. This process is repeated, with each layer being applied and adhered to the previous one. The number of layers varies depending on the building’s needs, but most BUR systems consist of three to five layers.
4. Final Layer: The final layer is typically composed of gravel ballast or a reflective coating. The gravel is spread evenly across the surface of the roof, while a reflective coating may be applied in some cases to enhance energy efficiency and UV protection.
5. Inspection and Curing: After installation, the roof is inspected for any gaps or defects. The roofing system needs to cure properly, especially if bitumen was used, as it needs time to fully adhere and settle into the layers.

Advantages of Built-Up Roofing

Built-up roofing systems have several advantages, making them a popular choice for commercial and industrial applications. Below are some of the key benefits of choosing BUR:

1. Durability and Longevity

One of the primary benefits of built-up roofing is its durability. A well-installed BUR system can last between 20 to 30 years or more with proper maintenance. The multiple layers of bitumen and reinforcing materials provide excellent protection against physical damage, weather elements, and UV radiation. Furthermore, the gravel or reflective coating helps to minimize damage from environmental exposure.

2. Waterproofing Properties

BUR systems are known for their exceptional waterproofing properties. The multiple layers of bitumen form a strong, impermeable barrier that effectively prevents water from penetrating the roof. This makes built-up roofing ideal for flat roofs or low-slope roofs, which are prone to water pooling.

3. Energy Efficiency

A reflective coating or white gravel ballast can be applied to the top layer of a built-up roofing system to improve the energy efficiency of a building. These materials reflect solar radiation, reducing the heat absorbed by the roof and lowering the building’s cooling costs. In hot climates, this feature can significantly reduce energy consumption, making BUR an eco-friendly choice.

4. Fire Resistance

BUR systems are often considered fire-resistant, especially when made with asphalt-based materials. The multiple layers of bitumen provide a degree of fire resistance, and the gravel layer helps to protect the roofing materials from the effects of heat and flame. This makes BUR a suitable option for buildings in areas prone to wildfires or high heat.

5. Low Maintenance

Built-up roofing requires relatively low maintenance. The durability of the materials means that repairs and replacements are infrequent. However, regular inspections are recommended to ensure that the system remains in good condition, particularly to check for any damage to the gravel or reflective coating.

Considerations for Built-Up Roofing

While built-up roofing offers numerous advantages, it is important to consider certain factors before opting for this system:

1. Weight of the System

One of the main considerations with built-up roofing is the weight of the system. The layers of bitumen, felt, and gravel can make BUR a relatively heavy roofing option. This weight can place additional strain on the building’s structural components, so it’s essential to ensure that the building can support the weight of the system before installation.

2. Installation Time

The installation process for built-up roofing can take longer than other roofing systems due to the number of layers involved. Additionally, the use of hot asphalt requires careful handling and can take several days to complete, depending on the size of the roof.

3. Odor and Fumes

The use of hot asphalt in the installation process can produce strong odors and fumes, which may be unpleasant for occupants or workers. Proper ventilation and precautions are necessary during installation to minimize exposure to these fumes.

4. Higher Initial Cost

Although BUR is a long-lasting and durable roofing system, the initial cost can be higher than other roofing options. The materials, labor, and time required for installation can contribute to a higher upfront investment. However, the long-term durability and reduced maintenance costs can offset this initial expense.

Conclusion

In summary, built-up roofing is a proven, reliable roofing system that provides outstanding protection and durability, particularly for flat and low-slope roofs. With its multiple layers of bitumen, reinforcing felt, and gravel or reflective coatings, BUR offers superior waterproofing, energy efficiency, fire resistance, and long-lasting performance.

By understanding the components, installation process, advantages, and considerations of built-up roofing, construction professionals can make informed decisions about its suitability for their projects. BUR remains a popular choice for buildings where durability, energy efficiency, and protection from the elements are paramount.

For more information on built-up roofing systems and their application in construction, refer to the original article.