Built-Up Roof Repair:
Common Problems With BUR and Tar-and-Gravel Roofs
Built-up roofing has protected commercial buildings for generations. These systems are known for multiple layers, durable construction, and their ability to withstand demanding rooftop conditions.
However, they can also be difficult to diagnose when they leak.
For example, water may enter through a split, flashing detail, or penetration and then travel between layers before appearing inside. In addition, on gravel-surfaced roofs, the membrane is partly hidden from view. As a result, a repair that addresses only the first visible defect may miss the actual source or the extent of wet insulation.
For this reason, understanding how a built-up roof is constructed can help building owners make better decisions about repair, restoration, and replacement.
What is a built-up roof?
A built-up roof, often called BUR, uses multiple layers to create a durable commercial low-slope roofing system.
A traditional system may include:
- Roof deck
- Vapor retarder, when required
- Insulation
- Cover board
- Base sheet
- Multiple reinforcing plies
- Asphalt or another bituminous material
- Protective surfacing
Together, the reinforcing layers and bitumen form a continuous waterproof assembly. Surfacing may consist of gravel, mineral granules, or a coating.
Because the system is built in layers, it can also provide redundancy. As a result, damage to the surface does not always penetrate every layer immediately.
Why are there rocks on a built-up roof?
Gravel serves several purposes.
It can:
- Protect asphalt from UV exposure
- Reduce surface temperature
- Protect against light impact
- Add fire resistance as part of an approved assembly
- Help secure certain roofing systems
However, gravel can also make inspections and repairs more time-consuming because technicians may need to move it before they can examine the membrane.
Read more about why commercial roofs have rocks on them.
How long does a built-up roof last?
There is no single lifespan for every BUR system. Performance depends on:
- Number of plies
- Material quality
- Installation
- Insulation and deck condition
- Drainage
- Climate
- Foot traffic
- Maintenance
- Speed of repairs
A well-maintained built-up roof may provide decades of service. A roof with poor drainage, neglected flashing or widespread trapped moisture may deteriorate much sooner.
Condition matters more than age alone.
What causes built-up roof leaks?
Common causes include:
- Membrane splits
- Blisters
- Open laps
- Cracked flashing
- Failed pitch pockets
- Damaged penetrations
- Poor drainage
- Punctures
- Deteriorated edge details
- Open expansion joints
- Improper rooftop equipment work
Water may also enter through walls, HVAC units, or drains rather than the roof field.
What are membrane splits?
Splits are cracks or separations in the built-up membrane. They may develop from:
- Building movement
- Thermal expansion and contraction
- Insulation movement
- Stress at transitions
- Poor attachment
- Aging materials
Because gravel can hide the extent of the damage, a split can extend farther than it initially appears. Therefore, technicians need to identify the full affected area and correctly restore the reinforcing layers to make a lasting repair.
What are blisters on a built-up roof?
Trapped air or moisture between roofing layers can create raised areas called blisters.
Not every blister requires immediate repair. Cutting into a stable blister unnecessarily can create a leak. However, a blister may need attention when it:
- Breaks open
- Interferes with drainage
- Occurs in a high-traffic area
- Affects seams or flashing
- Continues growing
- Shows evidence of moisture
A professional should evaluate the condition before deciding whether to leave, monitor, or repair it.
Can a built-up roof self-heal?
Warm asphalt can soften in the sun, and minor surface marks may appear to close. That does not mean the roof has truly restored its original reinforcement or waterproofing.
Therefore, a roofing professional should still evaluate the damage, especially when a puncture may have reached multiple plies.
We explored this question in our blog about whether a built-up roof can self-heal from bullet damage.
Why are tar-and-gravel roof leaks hard to find?
Gravel covers the membrane and can conceal:
- Splits
- Open seams
- Previous repairs
- Punctures
- Surface deterioration
In addition, water may travel between plies or through wet insulation.
Because of these challenges, technicians may need to take several steps during a leak investigation, including:
- Moving gravel
- Examining interior water paths
- Inspecting flashing
- Moisture scanning
- Core samples
- Controlled water testing
The location of the ceiling stain may not match the rooftop entry point.
How is a built-up roof repaired?
The process depends on the damage and existing assembly.
A roofing technician may take the following steps to complete a built-up roof repair:
- Removing gravel from the work area
- Cleaning and preparing the surface
- Removing damaged or wet materials
- Replacing insulation when necessary
- Installing compatible reinforcing plies
- Restoring bitumen and flashing
- Replacing protective surfacing
Most importantly, technicians need to tie the repair into sound existing material. Otherwise, simply applying roof cement over gravel or dirt is unlikely to provide lasting performance.
Can wet insulation be repaired locally?
Yes, when moisture is limited to a defined area and surrounding materials remain serviceable.
The contractor may remove the affected roof layers, replace wet insulation, and rebuild the membrane.
However, when moisture is widespread, repeated small repairs may not create dependable long-term value. Therefore, a commercial roofing contractor may use moisture scanning and core samples to determine the extent of the problem before recommending a repair strategy.
What is the difference between built-up roofing and modified bitumen?
Both use asphalt-based materials, but they are manufactured and installed differently.
For instance, roofing crews build BUR systems in the field using multiple reinforcing plies and bitumen.
In contrast, manufacturers produce modified-bitumen roofing as sheets enhanced with polymers. Depending on the product, roofing crews can install these sheets with hot asphalt, cold adhesive, self-adhered methods, or heat-welding.
Although the two systems can look similar in some conditions, repair materials and methods must match the existing roof.
Can a built-up roof be coated?
Some built-up roofs can be restored with a compatible coating, but eligibility depends on:
- Attachment
- Moisture content
- Surface condition
- Flashing
- Drainage
- Coating adhesion
- Existing repairs
However, a contractor should not simply apply a coating over wet insulation. In addition, gravel may need to be removed or addressed through a system specifically designed for the condition.
Ultimately, contractors should use adhesion testing and manufacturer requirements to determine whether a roof is a good candidate for coating.
When should a built-up roof be replaced?
Replacement may be justified when:
- Moisture is widespread
- The membrane has extensive splitting
- Flashing failure is widespread
- The deck is damaged
- The assembly has lost attachment
- Repairs are becoming frequent and unreliable
- Restoration cannot provide meaningful service life
Even in these situations, your commercial roofing contractor should explain why repair or restoration is no longer practical before recommending replacement.
Repair what can be repaired
A built-up roof that leaks does not automatically need to be torn off. Many BUR systems can continue performing with accurate diagnosis, compatible repairs, and regular maintenance.
Weather Shield Roofing Systems evaluates the membrane, insulation, deck, flashing and drainage before recommending the next step. Our goal is to repair what can be repaired and replace only when the condition of the roof supports that decision.
If your built-up or tar-and-gravel roof is leaking, schedule a commercial roof inspection. We will document the condition and show you the available options.
Ben Cornell
Account Executive
Ben Cornell is a lifelong West Michigan resident who began his career in commercial roofing in 2006—originally just looking for a summer job to help pay for college. What started as temporary work quickly turned into a lasting career as he steadily advanced through roles in estimating, project management, service leadership, and sales. Today, he serves as an Account Executive at Weather Shield Roofing Systems, where he continues to thrive in a company that has supported his professional growth every step of the way. Ben’s long-standing commitment to the commercial roofing industry is fueled by his passion for helping clients and the strong team culture at Weather Shield.
