Built-Up Bituminous Roofing: Complete Guide to Installation, Benefits, and Maintenance

Built-Up Bituminous Roofing (BUR) is a traditional low-slope roofing system widely used on commercial and multifamily buildings across the United States. This guide explains what BUR is, how it’s installed, its advantages and limitations, maintenance practices, and cost considerations to help facility managers, building owners, and contractors make informed decisions. BUR remains relevant for durable, watertight flat roofs when properly specified and maintained.

Feature	Built-Up Bituminous Roofing (BUR)
Typical Lifespan	20–35 Years With Proper Maintenance
Common Roof Slope	Low Slope / Flat
Main Components	Multiple Bitumen-Saturated Felts, Gravel Or Cap Sheet
Primary Strength	Waterproofing, Redundancy, Fire Resistance

What Is Built-Up Bituminous Roofing

Built-Up Bituminous Roofing, often abbreviated as BUR, consists of alternating layers of bitumen (asphalt or coal tar) and reinforcing felts, finished with a surfacing such as gravel, aggregate, or a mineral cap sheet. The layered composition creates redundancy: multiple waterproofing membranes act as a single durable system.

Materials And Components

Key BUR components include bitumen (oxidized asphalt, atactic polypropylene (APP) modified asphalt, or coal tar), reinforcing felts (organic or fiberglass), and surfacing. Each material choice affects flexibility, UV resistance, and longevity.

Bitumen Types

Oxidized asphalt is traditional and economical but can become brittle over time. Modified asphalts (APP, SBS) improve elasticity and temperature performance. Coal tar has superior chemical resistance but is less common due to environmental and odor concerns. Choosing the proper bitumen aligns performance with climate and building use.

Reinforcing Felts And Ply Sheets

Felts provide tensile strength and dimensional stability. Fiberglass felts resist shrinkage and rot better than older organic felts. The number of plies (usually 3–5) determines redundancy and total membrane thickness. More plies generally equate to improved puncture resistance and longer service life.

Surfacing Options

Surfacing protects the membrane from UV, mechanical wear, and foot traffic. Common finishes include loose-laid gravel, embedded aggregate, mineral-surfaced cap sheets, or reflective coatings. Gravel ballast is effective for protection and fire resistance but adds dead load.

Types Of BUR Systems

BUR systems vary by bitumen type, number of plies, and surfacing. Common configurations include coal tar pitch BUR, asphalt BUR, and modified asphalt BUR. System selection reflects building code, budget, and performance targets.

Design Considerations

Proper BUR design addresses roof slope, drainage, insulation, flashing details, expansion joints, and rooftop equipment. Minimal slope should facilitate positive drainage to avoid ponding water. Incorporating tapered insulation can reduce ponding and extend membrane life.

Insulation And Deck Compatibility

Insulation types (polyiso, EPS, or gypsum board) must be compatible with BUR and provide adequate compressive strength under ballast. Decks can be concrete, steel, or wood; each requires different attachment and substrate preparation. Proper attachment and thermal control are critical to prevent membrane fatigue.

Installation Process

BUR installation is a multi-step process performed by trained roofers. Typical steps include substrate preparation, installation of insulation and base sheets, application of hot bitumen and felts, building up multiple plies, and applying the surfacing. Skilled workmanship ensures consistent bitumen coverage and proper seam formation.

Hot Application Versus Cold Adhesives

Traditional BUR uses hot-applied bitumen heated to specific temperatures for adhesion. Cold-applied mastics or adhesives exist for lower VOC and safety concerns but may change application speed and performance. Hot-applied systems require strict safety protocols and temperature control.

Quality Control And Testing

Inspection during installation should verify membrane thickness, ply alignment, bitumen coverage, flashing details, and surfacing consistency. Core sampling, moisture surveys, and infrared scans can confirm system integrity. Documented QC reduces future leak risk and warranty disputes.

Performance And Durability

BUR provides robust waterproofing, excellent fire resistance (with gravel surfacing), and high puncture resistance. Lifespan depends on materials, installation quality, climate exposure, and maintenance. A well-maintained BUR roof commonly achieves 20–35 years service life.

Weather And Climate Effects

UV radiation, thermal cycling, and freeze-thaw conditions affect asphalt brittleness and membrane fatigue. Modified asphalts offer better flexibility in extreme climates. Choosing materials matched to the climate improves longevity.

Maintenance Best Practices

Regular maintenance preserves BUR performance: inspections twice a year, after severe storms, and after rooftop work. Tasks include clearing debris, checking gravel distribution, sealing flashings, and repairing blisters or split seams. Prompt repairs prevent minor issues from becoming costly leaks.

Inspection Checklist

• Visual Check: Look for ponding, degraded gravel cover, open seams, and edge deterioration.
• Flashing Inspection: Ensure terminations at parapets, curbs, and penetrations are secure.
• Drainage: Verify drains and scuppers are clear and functioning.
• Roof Traffic Damage: Identify footprint wear from equipment or footpaths and protect with walk pads.

Common Repairs

Repairs include re-bedding loose gravel, patching with heat-welded sheets or mastic, and replacing damaged flashing. For localized deterioration, overlaying with a compatible cap sheet or single-ply can extend service life when allowed by structural load limits. Permanent repairs use compatible materials and proper detailing.

Costs And Life-Cycle Considerations

Initial BUR installation costs vary by region, roofing thickness, insulation needs, and surfacing choice. Typical installed costs are competitive with other low-slope options, though higher when multiple plies and ballast are used. Life-cycle costing often favors BUR where durability and fire resistance reduce long-term expenses.

Factors Affecting Cost

• Material Quality: Modified bitumens and fiberglass felts increase cost but improve lifespan.
• Roof Complexity: Penetrations, flashings, and parapets increase labor and detailing costs.
• Insulation And Structural Load: Tapered insulation or additional structural support raises total project cost.

Code, Environmental, And Sustainability Issues

Building codes often mandate fire performance and wind uplift resistance for commercial roofs. Some municipalities restrict coal tar due to VOC and polycyclic aromatic hydrocarbon concerns. Reflective surfacing or cool roof coatings can improve energy performance and may qualify for incentives. Sustainability improvements include recycled aggregate ballast and cool coatings to reduce urban heat effect.

Comparisons With Alternative Low-Slope Systems

BUR competes with single-ply membranes (TPO, PVC, EPDM), metal roofing, and spray polyurethane foam. Compared to single-ply membranes, BUR offers redundancy and proven longevity but is heavier and less easy to repair for small punctures. System selection balances weight, cost, ease of repair, and expected roof traffic.

When To Choose Built-Up Bituminous Roofing

BUR is appropriate for low-slope roofs where redundancy, fire resistance, and long-term waterproofing are priorities. It suits buildings with sufficient structural capacity and owners who plan for long-term maintenance. BUR is especially useful for roofs with high foot traffic or heavy rooftop equipment.

Hiring Contractors And Warranties

Select contractors with BUR-specific experience, verified references, and manufacturer certifications. Written warranties should cover materials and workmanship, with clear terms on maintenance obligations. Request documented inspection and QC records as part of the turnover package.

Key Takeaways For Building Owners

Built-Up Bituminous Roofing remains a proven, durable option for low-slope commercial roofs when designed and maintained properly. Prioritize material selection matched to climate, skilled installation, and routine maintenance to maximize lifespan and performance. Long-term value from BUR depends on redundancy, surfacing protection, and proactive care.