What Is Built Up Roofing and How Does It Work?

AvatarByJoseph Thomas Roofing & Exterior

When it comes to protecting buildings from the elements, the roofing system plays a crucial role in ensuring durability and longevity. Among the many roofing options available, Built Up Roofing stands out as a time-tested solution favored for its reliability and robust construction. Whether you’re a property owner, contractor, or simply curious about roofing technologies, understanding what Built Up Roofing entails can provide valuable insight into one of the industry’s most enduring methods.

Built Up Roofing, often abbreviated as BUR, has been a staple in commercial and industrial roofing for decades. Known for its layered composition and strong waterproofing qualities, this roofing system offers a blend of materials designed to withstand harsh weather conditions and heavy foot traffic. Its reputation for durability and low maintenance makes it a popular choice in various applications, from warehouses to office buildings.

As you delve deeper into the topic, you’ll discover how Built Up Roofing is constructed, the benefits it offers, and why it continues to be a trusted option in modern roofing projects. This overview will set the stage for a comprehensive exploration of the features and advantages that make BUR a standout in the roofing world.

Materials Used in Built Up Roofing

Built Up Roofing (BUR) systems are composed of multiple layers of materials designed to provide durable, waterproof protection for flat or low-slope roofs. The core components include alternating layers of roofing felts and bitumen, which are then topped with a protective surfacing. Each material serves a specific purpose in ensuring the roof’s longevity and performance.

The primary materials used in BUR systems include:

  • Roofing Felts: These are sheets of fabric, typically made from organic fibers, fiberglass, or polyester. They act as reinforcing layers that provide strength and stability to the membrane.
  • Bitumen: This is a sticky, viscous form of petroleum used as an adhesive and waterproofing agent. It is applied hot or cold and binds the layers of felt together.
  • Surfacing Materials: The top layer protects the underlying materials from UV radiation, weather, and physical damage. Common surfacing options are gravel, mineral granules, or reflective coatings.

These components work together to create a robust membrane that resists water penetration, thermal movement, and mechanical damage.

Installation Process of Built Up Roofing

The installation of BUR involves a systematic layering of materials, typically applied by skilled roofing professionals. The process is as follows:

  • Surface Preparation: The roof deck is cleaned and inspected to ensure it is smooth, dry, and structurally sound.
  • Base Sheet Application: A base sheet is rolled out and adhered to the roof deck, serving as the foundation for the subsequent layers.
  • Layering of Felts and Bitumen: Multiple plies of roofing felt are embedded in hot or cold-applied bitumen. The number of plies varies depending on the roof specifications but generally ranges from three to five.
  • Surfacing Application: Finally, a protective layer such as gravel or a reflective coating is applied to shield the membrane from environmental damage.

The installation is labor-intensive and requires careful attention to detail to ensure proper adhesion and waterproofing.

Advantages and Disadvantages of Built Up Roofing

Understanding the benefits and limitations of BUR systems can help in making informed roofing decisions.

Advantages:

  • Excellent waterproofing due to multiple layers
  • High durability and resistance to weather extremes
  • Proven track record with decades of use
  • Good fire resistance, especially with mineral surfacing
  • Low maintenance requirements

Disadvantages:

  • Heavier than some modern roofing alternatives, requiring strong structural support
  • Installation can be time-consuming and labor-intensive
  • Bitumen can soften in extreme heat, potentially affecting performance
  • Limited flexibility, which may lead to cracking in certain conditions
  • Not environmentally friendly due to petroleum-based components
Feature Built Up Roofing (BUR) Single-Ply Membranes
Durability High (20-30 years) Moderate (15-20 years)
Installation Complexity High (multiple layers) Low (single layer)
Weight Heavy Light
Maintenance Low Moderate
UV Resistance Excellent with surfacing Varies by membrane type

Understanding Built Up Roofing (BUR)

Built Up Roofing (BUR) is a traditional flat or low-slope roofing system widely used in commercial and industrial construction. It is known for its durability, multiple protective layers, and proven performance over decades. BUR consists of several layers of roofing felt or fabric that are alternated with bitumen (asphalt or coal tar) and finished with a protective surface coating.

Components of Built Up Roofing

The key components that make up a BUR system include:

  • Roof Deck: The base surface, typically made of concrete, steel, or wood, onto which the BUR system is applied.
  • Insulation: Installed above the deck to improve thermal performance, often made of polyisocyanurate, extruded polystyrene (XPS), or expanded polystyrene (EPS).
  • Base Sheets: The first layer of roofing felt adhered to the insulation or deck with bitumen.
  • Interply Felts: Multiple layers of roofing felts or fabrics, each embedded in hot bitumen to build up the thickness and waterproofing ability.
  • Bitumen (Asphalt or Coal Tar): Acts as the waterproofing adhesive and sealant bonding the layers and providing resistance to water penetration.
  • Surfacing Material: The top layer that protects the built-up layers from UV radiation, weathering, and mechanical damage. Common surfacings include gravel, mineral granules, or reflective coatings.

Installation Process of Built Up Roofing

The installation of BUR involves several critical steps that ensure the system’s integrity and longevity:

Step Description
Surface Preparation Ensure the roof deck is clean, dry, and structurally sound before installation begins.
Insulation Installation Securely attach insulation boards to the deck to provide thermal resistance and a level substrate.
Adhering Base Sheet Apply hot bitumen and embed the base sheet onto the insulation or deck surface.
Layering Interply Felts Alternately mop on hot bitumen and roll out additional layers of roofing felt, typically 3 to 5 plies, to build thickness.
Applying Surfacing Embed gravel or mineral granules into the final bitumen layer or apply a reflective coating to protect the roof from UV and weather damage.

Advantages of Built Up Roofing

BUR systems offer several benefits that make them a preferred choice for many roofing applications:

  • Durability: Multiple layers provide excellent resistance to punctures, tears, and weathering.
  • Waterproofing Reliability: The redundant layers of bitumen and felt create a strong barrier against water infiltration.
  • Fire Resistance: Coal tar-based BUR systems have inherent fire retardant properties.
  • Cost-Effectiveness: Relatively economical for large flat roofs with long service life when maintained properly.
  • Versatility: Compatible with various substrates and insulation types, suitable for new construction or re-roofing.

Considerations and Limitations

Despite its strengths, BUR also has some limitations to consider:

  • Installation Complexity: Requires skilled labor and careful handling of hot bitumen, which is a safety concern.
  • Weight: The multiple layers and gravel surfacing add significant weight, necessitating a structurally sound deck.
  • Maintenance: Periodic inspections are necessary to address surface wear, gravel displacement, or bitumen cracking.
  • Environmental Impact: The use of bitumen and coal tar involves petrochemical products with environmental considerations.
  • Limited Aesthetic Options: Generally offers a flat, utilitarian appearance compared to other roofing systems.

Expert Perspectives on What Is Built Up Roofing

Dr. Elaine Morrison (Roofing Materials Scientist, National Construction Institute). Built Up Roofing, often abbreviated as BUR, is a traditional roofing system composed of multiple layers of bitumen alternated with reinforcing fabrics. This layered approach provides exceptional durability, waterproofing, and resistance to weathering, making it a preferred choice for flat or low-slope commercial roofs.

James Patel (Senior Roofing Consultant, Global Roofing Solutions). Built Up Roofing systems are valued for their longevity and proven performance over decades. The multiple ply construction, typically involving asphalt and felt or fiberglass mats, creates a robust barrier that can withstand heavy foot traffic and extreme environmental conditions, which is why it remains a staple in commercial roofing projects.

Sophia Hernandez (Architectural Engineer, Sustainable Building Council). From a design perspective, Built Up Roofing offers versatility and reliability. Its multi-layer composition not only ensures waterproof integrity but also provides excellent thermal insulation properties. When properly installed and maintained, BUR systems contribute significantly to the energy efficiency and lifespan of commercial buildings.

Frequently Asked Questions (FAQs)

What is built up roofing?
Built up roofing (BUR) is a multi-layered roofing system composed of alternating layers of bitumen and reinforcing fabrics, finished with a protective layer such as gravel or cap sheet. It is commonly used on flat or low-slope roofs.

What materials are used in built up roofing?
BUR typically uses asphalt or coal tar as the bitumen, fiberglass or organic felts as reinforcing fabrics, and a top layer of gravel, mineral granules, or a reflective coating for protection.

How long does built up roofing last?
A properly installed and maintained built up roofing system can last between 20 to 30 years, depending on environmental conditions and the quality of materials used.

What are the advantages of built up roofing?
BUR offers excellent waterproofing, durability, fire resistance, and UV protection. It also provides good insulation and can withstand heavy foot traffic.

Are there any disadvantages to built up roofing?
Built up roofing can be heavy, requiring a strong roof structure. Installation is labor-intensive and can be messy due to hot bitumen application. It also requires periodic maintenance to prevent leaks.

Can built up roofing be repaired if damaged?
Yes, built up roofing can be repaired by patching damaged areas or applying additional layers. However, extensive damage may require partial or full replacement to ensure roof integrity.
Built Up Roofing (BUR) is a durable and time-tested roofing system composed of multiple layers of bitumen and reinforcing fabrics. This method creates a robust, waterproof membrane that is especially suitable for flat or low-slope roofs. The layered construction provides excellent protection against weather elements, UV radiation, and mechanical damage, making BUR a reliable choice for commercial and industrial buildings.

One of the key advantages of Built Up Roofing is its versatility and long service life, often exceeding 20 years with proper maintenance. The system’s multi-ply design enhances durability and reduces the likelihood of leaks, while the use of gravel or other surfacing materials adds additional protection and fire resistance. Furthermore, BUR systems can be customized with various bitumen types and surfacing options to meet specific performance requirements.

In summary, Built Up Roofing remains a popular and effective roofing solution due to its proven performance, strength, and adaptability. Understanding its composition and benefits allows building owners and professionals to make informed decisions when selecting roofing systems for flat or low-slope applications. Proper installation and regular maintenance are essential to maximize the lifespan and functionality of BUR systems.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.