What Is Built-Up Roofing (BUR) and How It Works

Built-Up Roofing, commonly called BUR, is a traditional flat roofing system used on many commercial and low-slope residential buildings across the United States. It combines multiple layers of reinforcing fabric and bitumen to create a durable, weatherproof membrane. This article explains what BUR roofing is, how it is constructed, its advantages and drawbacks, cost considerations, maintenance practices, and how it compares to modern alternatives.

Feature	Summary
System Type	Multiple layers of ply and bitumen (tar/asphalt)
Best For	Flat or low-slope commercial roofs
Life Expectancy	20–35+ years with maintenance
Cost Range	Moderate to High Initial Cost; Low to Moderate Lifecycle Cost
Common Issues	Thermal stress, ponding water, membrane cracks

What Built-Up Roofing (BUR) Is

Built-Up Roofing (BUR) is a multilayered roofing assembly composed of alternating layers of bitumen and reinforcing felts or fabrics. It is often finished with a surfacing material such as gravel, mineral granules, or reflective coatings. BUR creates a thick, continuous membrane that resists water infiltration and provides redundancy through multiple plies.

Key Components Of A BUR System

A typical BUR assembly includes a roof deck, insulation, vapor barrier (where required), multiple plies of roofing felt embedded in hot or cold-applied bitumen, and a protective surfacing layer. The number of plies commonly ranges from three to five, depending on performance requirements and local building codes.

Deck And Insulation

The roof deck may be concrete, metal, plywood, or gypsum board. Insulation boards—typically polyisocyanurate, EPS, or fiberglass—are installed to improve energy performance. Proper insulation and deck preparation are critical to prevent thermal movement and moisture issues.

Bitumen And Felts

Bitumen is the waterproofing agent and can be asphalt, coal tar, or modern modified asphalts. Roofing felts or fabrics (glass fiber or organic mats) provide tensile strength and crack resistance. The combination of bitumen and felts forms the waterproof membrane that defines BUR.

Surfacing

Surfacing options include loose gravel, crushed stone, mineral-surfaced capsheets, or reflective coatings. Surfacing protects the membrane from UV degradation, physical wear, and foot traffic. Gravel surfacing also improves fire resistance and ballast weight distribution.

How BUR Is Installed

Installation typically involves cleaning and preparing the deck, installing insulation, and then applying successive layers of felt saturated or embedded in hot-applied asphalt or coal tar. Gravel or other surfacing is applied while the bitumen is still tacky or using adhesives. Skilled roofing crews and adherence to manufacturer specifications are essential for long-term performance.

Advantages Of Built-Up Roofing

BUR has a long track record and offers several benefits that make it a trusted choice for low-slope roofs. Its multilayer construction provides redundancy—minor membrane damage is less likely to cause immediate leaks.

• Durability: Proven longevity when properly installed and maintained.

• Waterproofing Strength: Thick, continuous membrane resists ponding water better than single-ply systems in many cases.

• Fire Resistance: Coal tar or asphalt layers with mineral surfacing provide improved fire protection.

• Cost-Effective Over Time: Reasonable initial cost and predictable lifecycle costs with proper maintenance.

• Repairability: Localized repairs are often straightforward—patches and overlay techniques are common.

Limitations And Common Issues

Despite strengths, BUR systems have drawbacks. Some limitations include weight, installation complexity, and sensitivity to roof slope and drainage. Identifying and addressing weaknesses early prevents small problems from becoming large failures.

• Weight: Multiple layers and ballast add significant dead load; structural evaluation may be necessary for older buildings.

• Installation Hazards: Hot-applied asphalt or coal tar requires experienced crews and safety measures to manage heat and fumes.

• Ponding Water: Extended standing water accelerates membrane degradation and promotes leaks.

• Thermal Movement: Temperature fluctuations can cause cracking or splitting without proper detailing and expansion provisions.

• UV Sensitivity Without Surfacing: Bitumen degrades under UV exposure; the surfacing layer is essential for longevity.

Costs And Lifespan

Initial installation costs vary by region, materials, and roof complexity. Generally, BUR costs compare favorably to other high-quality low-slope systems. With routine maintenance, BUR can provide 20–35 years of service; advanced systems or overlays can extend life further.

Factors influencing cost and lifespan include the number of plies, type of bitumen (asphalt vs. coal tar), surfacing choice, insulation upgrades, roof slope, and existing deck condition. Routine inspections and timely repairs significantly affect lifecycle costs.

Maintenance Best Practices

Routine maintenance helps maximize BUR life expectancy. A proactive program includes twice-yearly inspections, after-storm checks, and yearly debris removal. Addressing issues like ponding, flashings, and blisters early can prevent major repairs.

1. Inspect Flashings And Seams: Flashings are common leak points; ensure they are secure and sealed.

2. Clear Drainage Paths: Remove debris from drains, scuppers, and gutters to prevent ponding.

3. Repair Blisters And Cracks: Cut out and patch damaged sections using compatible materials.

4. Reapply Surfacing Or Coatings: Reflective or protective coatings can restore UV protection and reduce heat gain.

5. Schedule Professional Inspections: Certified roofers can detect hidden issues such as wet insulation or deck deterioration.

BUR Vs. Single-Ply And Other Systems

Comparing BUR to single-ply membranes (TPO, EPDM, PVC) and modified bitumen reveals trade-offs in cost, weight, installation, and durability. BUR excels in redundancy and ponding resistance while single-ply systems offer lightweight, faster installs, and often superior seam performance.

Feature	BUR	Single-Ply (TPO/EPDM/PVC)
Weight	Heavy	Light
Installation Time	Longer (hot application)	Faster (factory-fabricated sheets)
Seam Durability	Seams Are Integral; Good Redundancy	Seam Quality Critical; Mechanically Fastened Or Heat-Welded
Lifespan	20–35 Years	15–30+ Years (varies)
Cost	Moderate To High Initial; Lower Long-Term	Moderate Initial; Variable Lifecycle

When To Choose BUR

BUR is a solid choice for buildings with low slopes, where durability, fire resistance, and redundancy are priorities. It is often selected for municipal buildings, warehouses, schools, and older commercial structures. Owners who value proven performance and can accommodate the weight and installation process frequently prefer BUR.

Environmental And Energy Considerations

Modern BUR systems can incorporate reflective coatings to reduce heat absorption and lower cooling loads. Recycled content in gravel or modified asphalt options can improve environmental profiles. Proper insulation and cool roof coatings help meet energy codes and reduce operating costs.

Common Questions About BUR

Can BUR Be Repaired Or Replaced In Sections?

Yes. Localized repairs and patches are common for BUR. Overlaying with new BUR or single-ply membranes is feasible if the deck supports the weight and the existing system is in acceptable condition. Assessment by a qualified roofing contractor is essential before overlays.

Is BUR Suitable For Residential Use?

BUR is more common on commercial buildings, but it is used on low-slope residential structures like townhomes or modern flat-roof homes. Weight and installation complexity often make alternatives like single-ply more attractive for many homeowners. Structural review and proper detailing are mandatory for residential BUR installations.

How Long Does A BUR Installation Take?

Project duration depends on roof size, weather, and deck preparation needs. Small commercial roofs may take a few days, while large projects can span several weeks. Weather windows are critical because hot-applied processes require dry conditions. Scheduling flexibility helps ensure quality and safety during installation.

Choosing A Contractor And Specifications

Selecting an experienced contractor familiar with BUR techniques and local code requirements is crucial. Contractors should provide manufacturer-specific details, warranties, and maintenance plans. Verify licensing, references, insurance, and whether the contractor offers a workmanship warranty in addition to material warranties.

Key Takeaway

Built-Up Roofing (BUR) remains a reliable, time-tested option for low-slope roofs where durability, redundancy, and fire resistance matter. Proper design, skilled installation, and regular maintenance are the keys to achieving a long service life and cost-effective performance.