built Up Roof: 9 Essential Facts About BUR Roofing

A Built Up Roof (BUR) is a traditional roofing system made with several layers of bitumen and reinforcing materials. It is mainly used on flat and low-slope roofs, especially on commercial and industrial buildings.

You may also hear it called a tar and gravel roof, multi-ply roofing, or BUR roofing.

Unlike a single-layer membrane, Built up roof uses several layers to create a thick roofing system. These layers work together to resist water, weather, foot traffic, and surface damage.

Built up roofing has been used for many years because of its durability and strong waterproofing ability. Modern BUR systems can also use different surfacing materials and installation methods based on the building and roof design.

But is a built up roof right for your property?

That depends on the roof structure, budget, climate, drainage, expected foot traffic, and the type of protection you need. This guide explains how BUR works, its benefits and drawbacks, how long it can last, and how it compares with other flat roofing systems.

What Is a Built Up Roof?

A built-up roof is a multi-layer roofing system made by combining bitumen with reinforcing sheets or fabrics.

Bitumen acts as the waterproofing material. The reinforcing plies add strength and help create a more durable membrane.

A typical Built up roof assembly may include:

• Roof deck
• Insulation
• Base sheet
• Bitumen
• Reinforcing felt or fabric
• Additional bitumen
• Multiple reinforcing plies
• Protective surface

The exact number and type of layers depend on the roof design and specifications.

The system is called “built up” because the waterproofing membrane is created by building several layers over one another.

Traditional systems often use gravel or crushed stone as the top surface. Other systems may use mineral cap sheets or reflective coatings. The surface helps protect the roof from sunlight, weather, and physical damage.

How Does BUR Roofing Work?

The main idea behind BUR is simple: multiple layers create a strong, continuous waterproof barrier.

Instead of depending on one membrane, the roof has several reinforcing plies separated or embedded in bitumen.

If the top surface receives minor damage, the layers below can continue providing protection.

The roof still needs proper installation and maintenance. Multiple layers do not make the roof immune to leaks. Poor flashing, standing water, damaged surfaces, or installation defects can still cause problems.

A built up roof also needs a slight slope so water can drain toward drains or scuppers. A flat-looking roof should not be completely level.

Proper drainage is especially important because standing water can increase stress on the roofing system over time.

What Are the Layers of a Built Up Roof?

Understanding the layers makes it easier to understand why BUR is durable.

1. Roof Deck

The roof deck forms the structural base of the roofing system.

It may be made from materials such as concrete, metal, or wood, depending on the building.

The deck needs to be suitable for the roofing assembly and strong enough to support the completed system.

2. Insulation

Insulation may be installed as part of the roof assembly.

It can help control heat transfer and improve the building’s energy performance.

The type and location of insulation depend on the roof design, building requirements, and climate.

3. Base Sheet

The base sheet creates a foundation for the upper roofing layers.

It may be attached mechanically or with an adhesive system, depending on the project.

4. Bitumen

Bitumen is the waterproofing material used between the reinforcing layers.

It binds the plies together and helps create a continuous membrane.

5. Reinforcing Plies

These sheets are placed between layers of bitumen.

They can be made from fiberglass or other reinforcing materials. More plies generally create a thicker and more robust system, although the exact design should be selected by a roofing professional.

6. Surface Protection

The top of the roof needs protection from weather and sunlight.

Gravel, mineral surfacing, or a coating may be used depending on the BUR design.

Gravel can provide UV protection and added resistance to physical damage. Smooth systems can use reflective coatings or other materials to provide surface protection.

9 Important Benefits of a Built Up Roof

BUR remains useful because its layered design provides several advantages.

1. Strong Waterproofing

One of the biggest reasons property owners choose Built up roof is its waterproofing ability.

Multiple bitumen and reinforcing layers create a thick barrier against water. When the system is properly installed, it can provide reliable protection for flat and low-slope buildings.

This makes BUR useful for commercial properties where roof leaks can damage equipment, inventory, ceilings, insulation, and interior spaces.

2. Durable Construction

The built up roof is designed to withstand demanding roof conditions.

The multiple layers can provide resistance to weather, normal foot traffic, and minor surface damage.

A well-installed and maintained system can remain functional for many years.

3. Long Service Life

A built up roof can often last 20 to 30 years or more when it is properly designed, installed, inspected, and maintained. Actual service life varies based on materials, workmanship, drainage, climate, roof traffic, and maintenance.

A roof that is neglected may fail much sooner.

4. Good Resistance to Foot Traffic

Commercial roofs often need access for HVAC equipment, vents, electrical equipment, and maintenance.

The layered BUR structure can handle routine maintenance traffic better than some more vulnerable roof surfaces.

However, that does not mean people should walk across the roof unnecessarily. Heavy or repeated traffic can still damage roofing materials.

5. UV Protection

Sunlight can gradually damage exposed roofing materials.

A gravel surface can help shield the roofing layers from ultraviolet radiation. Other BUR systems can use reflective coatings or other protective finishes.

The right surface depends on the building’s needs and climate.

6. Fire Resistance

Some Built up roof assemblies can provide strong fire resistance when properly designed with approved materials.

Fire performance depends on the complete roof assembly, not simply the fact that the roof is BUR.

Building owners should review the specific fire rating required for their property.

7. Repairable Surface

Small areas of damage can sometimes be repaired without replacing the entire roof.

A roofing professional can inspect the affected area and determine whether a localized repair, coating, restoration, or replacement is appropriate.

8. Proven Technology

Built up roof has a long history in commercial roofing.

It has remained in use because the basic multi-layer concept provides reliable waterproofing and durability when properly installed.

9. Flexible Surfacing Options

Built up roof does not have to look exactly like an old-fashioned tar-and-gravel roof.

Depending on the system, property owners may have options such as gravel, mineral surfacing, or reflective coatings.

This allows the roofing system to be selected based on performance requirements and building conditions.

What Are the Disadvantages of a Built Up Roof?

BUR has important advantages, but it is not the best choice for every building.

It Can Be Heavy

Multiple roofing layers and gravel surfacing add significant weight.

Before installing BUR on an existing building, the roof structure should be evaluated to make sure it can support the proposed system.

This is especially important when replacing a lightweight roofing membrane with a heavier assembly.

Installation Can Take Longer

BUR involves several layers and requires careful installation.

The work may take longer than installing some single-ply systems because each layer must be properly applied.

The quality of the installation has a major effect on roof performance.

Hot Bitumen Can Produce Odors

Some BUR installation methods use hot-applied asphalt.

This can create odors and fumes during installation. Proper safety procedures and ventilation are important, particularly around occupied buildings.

Leak Detection Can Be More Difficult

A BUR roof contains several layers, so finding the exact source of a leak may not always be simple.

Water can sometimes travel between layers before appearing inside the building.

This is one reason professional roof inspections are important.

Repairs May Require Surface Removal

Gravel or other protective surfacing can make some repairs more involved.

A professional may need to move or remove surface material to inspect the membrane underneath.

It Needs Good Drainage

BUR is not designed to sit under standing water indefinitely.

Blocked drains, poor slope, damaged flashing, and other drainage problems can increase the risk of roof deterioration.

How Long Does a Built Up Roof Last?

The expected lifespan of a BUR system is often around 20 to 30 years or more, but there is no single number that applies to every roof.

Several factors affect its service life.

Installation Quality

Poor installation can create weak points that lead to premature failure.

Number of Plies

The design and number of reinforcing layers affect the system’s construction and performance.

Roof Drainage

Water should have a clear path to drains or scuppers.

Climate

Strong sunlight, heavy rain, snow, ice, wind, and repeated temperature changes can affect roofing materials.

Roof Traffic

Regular maintenance access can be handled, but unnecessary traffic can increase wear.

Maintenance

Regular inspections can identify problems before they become major leaks.

Built Up Roof vs. Modified Bitumen

BUR and modified bitumen are both asphalt-based roofing systems, but they are constructed differently.

BUR is assembled using multiple layers of bitumen and reinforcing plies.

Modified bitumen roofing uses factory-made sheets that contain modified asphalt and reinforcing materials.

Modified bitumen can be installed using different methods, including self-adhered, cold-applied, or heat-welded systems.

BUR is often chosen when a property owner wants a traditional multi-ply system. Modified bitumen can offer a simpler membrane installation.

The right choice depends on the roof structure, building use, installation conditions, and project requirements.

Built Up Roof vs. EPDM

EPDM is a single-ply synthetic rubber membrane commonly used on low-slope roofs.

The biggest difference is construction.

BUR uses several layers of bitumen and reinforcing materials. EPDM uses a flexible rubber membrane.

EPDM is generally lighter and can be installed efficiently on many buildings.

BUR, on the other hand, provides a thick multi-layer assembly and has a long history in commercial roofing.

Neither system is automatically better for every building.

The best option depends on the roof’s size, structure, climate, drainage, budget, and expected use.

Built Up Roof vs. TPO

TPO is another single-ply roofing membrane commonly used on commercial buildings.

TPO systems can offer reflective surfaces and relatively fast installation.

BUR offers a different approach based on multiple layers.

For a building owner, the decision should not be based only on the material name. Consider installation conditions, energy goals, expected foot traffic, maintenance requirements, roof structure, and long-term performance.

A roofing professional can compare the systems based on the actual property.

When Is a Built Up Roof a Good Choice?

BUR may be a good option when a building has a low-slope roof and needs a durable, multi-layer waterproofing system.

It can be especially useful for:

• Commercial buildings
• Warehouses
• Industrial buildings
• Schools
• Office buildings
• Retail properties
• Buildings with regular roof maintenance access
• Low-slope roofs requiring strong waterproofing

BUR is not automatically the right choice just because a roof is flat.

The building’s structural capacity, drainage, existing roofing system, and project budget should be reviewed first.

What Are the Signs a BUR Roof Needs Repair?

Do not wait for a major interior leak before inspecting the roof.

Look for warning signs such as:

Blisters

Raised areas may indicate trapped air or moisture within the roofing assembly.

Cracks and Splits

Visible cracks can allow water to enter the roofing system.

Damaged Flashing

Flashing around walls, curbs, vents, and other penetrations is a common area to inspect.

Ponding Water

Water that remains on the roof after weather has passed may indicate a drainage problem.

Loose or Missing Gravel

On gravel-surfaced BUR systems, displaced areas can expose the roofing layers to more sunlight and physical wear.

Interior Water Damage

Ceiling stains, damp insulation, peeling paint, or water around roof penetrations may indicate a roofing problem.

These signs do not always mean the entire roof needs replacement. A professional inspection can determine the actual condition.

How Do You Maintain a Built Up Roof?

Regular maintenance can help extend the useful life of a BUR system.

A basic maintenance plan should include:

• Inspecting the roof regularly
• Keeping drains and scuppers clear
• Removing damaging debris
• Checking flashing
• Looking for cracks and blisters
• Checking areas around rooftop equipment
• Watching for ponding water
• Inspecting gravel distribution
• Repairing small problems early

Roof inspections should be performed by qualified professionals, especially when the roof is large, difficult to access, or showing signs of failure.

Regular maintenance can help prevent a small roofing issue from becoming an expensive interior repair.

Should You Repair or Replace a Built Up Roof?

The answer depends on the condition of the existing system.

Repair may make sense when damage is limited to a small area and most of the roofing system remains in good condition.

Restoration may be possible when the underlying roof is still suitable but the surface needs additional protection.

Replacement may be needed when the membrane has widespread deterioration, repeated leaks, severe moisture damage, structural problems, or has reached the end of its useful life.

Do not make this decision based only on the roof’s age.

A professional inspection should consider the condition of the membrane, flashing, insulation, drainage, roof deck, and other components.

How Much Does Built Up Roofing Cost?

There is no single price for a BUR installation.

The total cost can depend on:

• Roof size
• Number of plies
• Insulation
• Surface material
• Existing roof removal
• Roof accessibility
• Drainage work
• Flashing
• Labor
• Structural requirements
• Local material prices

A replacement project can also cost more if the existing roof needs extensive tear-off or the roof deck requires repairs.

For this reason, online price ranges should only be treated as general estimates. A contractor should inspect the property and provide a project-specific quote.

Frequently Asked Questions About Built Up Roofs

What is a built up roof?

A built-up roof is a multi-layer roofing system made from alternating layers of bitumen and reinforcing materials. It is commonly used on flat and low-slope commercial roofs.

Why is it called a built up roof?

It is called a built-up roof because the waterproofing membrane is created by building multiple layers of bitumen and reinforcing plies over the roof deck.

Is BUR the same as a tar and gravel roof?

The terms are often used together because traditional BUR systems commonly use gravel as a protective surface. However, modern BUR systems can use other surfacing materials as well.

How many layers does a BUR roof have?

The number of layers varies by system design. BUR can use several reinforcing plies with bitumen between them. The required assembly should be based on the building and project specifications.

Is BUR good for a flat roof?

Yes. BUR is designed primarily for flat and low-slope roofing applications. The roof still needs proper drainage so water can move toward drains or scuppers.

Is a built up roof waterproof?

BUR is designed to provide strong waterproofing, but no roofing system is completely maintenance-free. Poor installation, damaged flashing, ponding water, and aging materials can still cause leaks.

How long does a BUR roof last?

A properly installed and maintained BUR system can often last 20 to 30 years or more. Actual lifespan depends on materials, installation, drainage, climate, maintenance, and roof use.

Is BUR better than EPDM?

Neither system is best for every project. BUR provides a multi-layer asphalt-based system, while EPDM uses a single rubber membrane. The right choice depends on the building, roof structure, budget, climate, and performance goals.

Is BUR better than TPO?

TPO and BUR use different roofing approaches. TPO is a single-ply membrane, while BUR is a multi-layer system. A professional should compare the two based on the building’s specific requirements.

When should a BUR roof be replaced?

Replacement may be necessary when the roof has widespread deterioration, repeated leaks, severe moisture problems, damaged decking, or has reached the end of its useful service life.

How USA Builders and Developers Can Help

Choosing the right roofing system is an important decision, especially for a flat or low-slope building. If you are dealing with an aging roof, leaks, ponding water, or other roofing concerns, USA Builders and Developers can help assess the problem and recommend the right next step.

Our roofing services include solutions for different roof types and property needs. We can also help with related waterproofing and exterior work when moisture problems extend beyond the roof.

Whether your property needs roof repair, roof replacement, waterproofing, or other exterior construction services, getting the problem inspected early can help prevent more serious damage.

Contact USA Builders and Developers to discuss your roofing needs and find a practical solution for your property.

Final Thoughts

A Built Up Roof is a durable, multi-layer roofing system designed mainly for flat and low-slope roofs. Its combination of bitumen and reinforcing plies creates a strong waterproofing barrier that has made BUR a long-standing choice for commercial and industrial properties.

Its biggest strengths include durability, waterproofing, surface protection, and resistance to normal roof traffic. Its main drawbacks include weight, installation complexity, potential odors during some installation methods, and the need for regular maintenance.

The best roofing system is not simply the one with the longest list of benefits. It is the one that fits your building, roof structure, climate, drainage, budget, and long-term goals.

If your property has a BUR system, regular inspections and early repairs can help protect your investment and extend the roof’s useful life.

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