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What Is Built-Up Roofing?

August , 2023 | 6 min. read

By David Toth

worker standing on roof

In the realm of commercial roofing systems, where durability, weather resistance, and longevity are paramount, one solution has stood the test of time: Built-Up Roofing. Often recognized as the "tar and gravel" roofing method, BUR has been a reliable choice for decades, offering a tried-and-true approach to creating resilient, multi-layered roofing systems.

With its intricate layering of bitumen, reinforcing fabrics, and protective surfacing, BUR has carved a niche for itself in the roofing industry, particularly for commercial and industrial structures with flat or low-sloped roofs. Here at RoofCrafters, we’ve been installing built-up roofing systems for our friends with commercial properties for decades, and we’ve seen that just as with fashion and technology, roofing trends seem to come and go over the years; but not BUR.

This specific system is always in style and remains one of the most popular roofing choices on the market today. So, what makes it so special? Gee, I’m glad you asked! In just a few short moments, you’ll learn exactly what built-up roofing is, what it’s made of, its advantages, and the types of properties that BUR is best used on. So, without further ado, let’s jump right in!

What Is Built-Up Roofing?


built up

Built-Up Roofing (BUR), also known as "tar and gravel roofing," is a type of roofing system commonly used in commercial and industrial buildings. It's a traditional, durable method of creating a waterproof, watertight roof surface. BUR consists of multiple layers of bitumen (asphalt or coal tar) and reinforcing fabrics, typically fiberglass or organic materials like felt, that are alternately layered and then mopped or hot-applied with bitumen to create a strong, cohesive roofing membrane.

Here's a breakdown of the typical components in a Built-Up Roofing system:

Base Sheet: A base layer of asphalt-saturated felt or fiberglass mat is laid down as the initial layer. This provides a stable substrate for the rest of the roofing system.

Bitumen Layer: Hot bitumen (asphalt or coal tar) is applied over the base sheet, saturating it and forming a waterproofing layer.

Reinforcing Fabric: A layer of reinforcement, often fiberglass or organic felt, is placed over the bitumen layer to add strength and stability to the roofing system.

Bitumen Interply Sheets: More layers of bitumen-saturated felt or fiberglass are added, sandwiching the reinforcing fabric between them. These layers are known as "plies."

Surfacing: The top layer of the BUR system is often a protective and weather-resistant surfacing material, which can be gravel, mineral granules, or a reflective coating. This layer provides UV protection, helps manage water runoff, and protects the underlying layers from environmental damage.

Built-Up Roofing Offers Several Advantages


BUR has many amazing advantages and great qualities that come with investing in the system, which include:

  1. Durability: BUR systems are known for their longevity. The multiple layers and redundant construction provide excellent resistance to weathering and wear.
  2. Fire Resistance: Coal tar-based BUR systems offer superior fire resistance, making them suitable for buildings with strict fire code requirements.
  3. Weatherproofing: The layered construction and use of bitumen create a waterproof and weather-resistant barrier that can withstand a variety of weather conditions.
  4. Thermal Performance: The multiple layers of insulation and thermal mass in a BUR system can provide good thermal insulation for the building.

roofer doing a repair to vents on a hot tar roof with rocks

However, there are also some considerations...

Weight: BUR systems are heavy due to the multiple layers, which may require structural reinforcement to support the load.

Installation Complexity: The installation process involves hot asphalt or tar, which requires skilled labor and specialized equipment.

Maintenance: Over time, BUR systems may require maintenance such as re-sealing or re-surfacing to maintain their performance.

In recent years, newer roofing technologies such as single-ply membranes (EPDM, TPO, PVC) have gained popularity due to their lighter weight, ease of installation, and comparable durability. However, BUR still has its place in the roofing industry, particularly in applications where its advantages align with building requirements.

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When Is Built-Up Roofing Best Used?


Built-Up Roofing (BUR) systems are best suited for specific types of properties and situations where their unique characteristics align with the building's needs. Here are some types of properties and situations where BUR is commonly used:

  • Commercial and Industrial Buildings: BUR systems are often preferred for large commercial and industrial structures due to their durability and long lifespan. These buildings typically have flat or low-sloped roofs where BUR's layered construction can provide effective weatherproofing.
  • Low-Sloped Roofs: BUR is particularly well-suited for roofs with low slopes (typically slopes less than 3:12) where water drainage might be slower. The multiple layers of bitumen and reinforcement help prevent water infiltration.
  • High-Traffic Roofs: BUR's robust construction makes it suitable for roofs that may experience heavy foot traffic, such as roofs with equipment or HVAC installations that require regular maintenance.
  • Fire-Resistant Requirements: BUR systems, especially those using coal-tar bitumen, are highly fire-resistant. Therefore, they are often chosen for buildings where fire safety is a critical concern, such as industrial plants or warehouses storing flammable materials.
  • Extreme Weather Conditions: BUR systems are resilient to harsh weather conditions, making them suitable for regions with extreme temperatures, strong winds, and heavy precipitation.
  • Historic Buildings: In some cases, BUR may be chosen for historical or preservation purposes, as it replicates traditional roofing methods and may blend better with the aesthetics of older structures.
  • Roofs with Rooftop Gardens or Green Spaces: BUR systems can provide a sturdy foundation for rooftop gardens or green spaces due to their multiple layers, which can help protect the waterproofing membrane from potential damage.
  • Roofs Requiring Reflective Coatings: BUR systems can be paired with reflective coatings to improve energy efficiency and reduce cooling costs in warmer climates.

hot tar being mopped on a flat roof

The choice of roofing system should always take into consideration the specific needs of the property, local climate, budget, and other relevant factors. Consulting with roofing professionals or experts can help determine the best roofing solution for a particular project.

Is Built-Up Roofing a Good Choice for My Commercial Property?


Built-Up Roofing stands as a time-tested and durable roofing solution, appreciated for its resilience, weatherproofing capabilities, and fire-resistant properties. With its multiple layers of bitumen and reinforcing materials, BUR systems excel in protecting low-sloped and flat roofs, particularly in commercial, industrial, and high-traffic environments. Its ability to withstand extreme weather conditions, foot traffic, and potential hazards makes it a reliable choice for structures seeking long-term performance.

As you now know, BUR roofing offers numerous advantages, including its suitability for fire-sensitive locations and historical preservation projects, but the decision to use this system should be made in consideration of various factors. Such factors include the property's specific requirements, budget constraints, and available roofing alternatives like single-ply membranes. Engaging with roofing experts can guide property owners in selecting the most appropriate roofing solution that aligns with the needs of their structure, climate, and intended use.

Built-Up Roofing's legacy lies in its ability to provide dependable protection for structures across a spectrum of industries and contexts. As roofing technologies continue to evolve, BUR remains a steadfast option for those seeking a robust, time-honored solution for their roofing needs. If you’re interested in BUR for your commercial property and are looking for an expert opinion, be sure to hit the “Schedule an Inspection” button down below, and one of our roofing professionals will meet with you at your earliest convenience to discuss your built-up roofing possibilities!

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David Toth

My name is David Toth and I am the lead estimator in North Florida with RoofCrafters Roofing. Originally from New Brunswick, I have called Florida home for the past 47 years. I enjoy cooking along with traveling to different historical areas in Florida when I have free time.