Asphalt Built-Up Roof Guide for Durable Low-Slope Roofing

The Asphalt Built-Up Roof (BUR) system is a long-standing choice for low-slope commercial and residential roofs, known for layered protection and fire resistance. This guide covers construction, materials, benefits, costs, maintenance, and replacement considerations to help property owners and managers make informed decisions about asphalt built-up roofing solutions.This guide focuses on practical details, life expectancy, and cost factors relevant to U.S. roofing markets.

Characteristic	Typical Value
Typical Lifespan	20–35 Years With Proper Maintenance
Common Membrane Types	Asphalt-Saturated Felts, Cold-Applied Adhesives, Torch-Applied Systems
Primary Benefits	Durability, Multi-Layer Protection, Fire Resistance
Typical Cost Range	$5.00–$10.00 Per Sq Ft Installed

What Is An Asphalt Built-Up Roof

An Asphalt Built-Up Roof (BUR) consists of alternating layers of bitumen (asphalt or coal-tar pitch) and reinforcing fabrics, typically fiberglass or organic felts, finished with a protective surfacing such as gravel, mineral granules, or reflective coatings. BUR is designed for low-slope roofs where layered redundancy delivers waterproofing and UV protection.

Types Of BUR Materials And Installation Methods

BUR systems vary by the type of bitumen and felts used and by the application method. Common options include mopped hot-applied asphalt, torch-applied bitumen, and cold-applied adhesives for safer installations.

Asphalt And Coal-Tar Pitch

Asphalt is the most common bitumen, valued for flexibility and UV resistance. Coal-tar pitch offers excellent moisture resistance and chemical tolerance but has environmental and odor concerns. Asphalt-based BUR is the mainstream choice in most U.S. regions.

Reinforcing Felts

Reinforcing felts are either organic (fibrous) or fiberglass. Fiberglass felts provide superior dimensional stability and resistance to tearing. Choosing the right felt composition affects durability and weight of the BUR assembly.

Surfacing Options

BUR surfacings include crushed stone (gravel), mineral-surfaced roll roofing, or reflective coatings such as aluminum coating or white elastomeric coatings. Surfacing selection influences fire rating, reflectivity, and maintenance frequency.

Performance And Lifespan

Lifespan depends on installation quality, climate, traffic, and maintenance. Properly installed BUR can last 20 to 35 years, sometimes longer with overlays and periodic recoating. Coastal and high-UV regions may see shorter lifespans without reflective surfacing.

Advantages Of Asphalt Built-Up Roofs

BUR systems offer several performance benefits that make them attractive for low-slope applications. Key advantages include redundancy, proven track record, and fire resistance.

• Redundancy Through Multiple Layers: Multiple plies provide backup protection against punctures and localized failures.
• Durability: Good resistance to foot traffic and mechanical damage when surfaced with gravel.
• Fire Resistance: Coal-tar and asphalt BURs can achieve strong fire ratings when properly surfaced.
• Repairability: Localized repairs are straightforward; felts and bitumen can be patched effectively.

Common Drawbacks And Limitations

Despite strengths, BUR has drawbacks to consider. Key limitations include weight, installation logistics, and sensitivity to temperature during installation.

• Heavy System Weight: Multiple layers and gravel surfacing increase dead load; structural assessment is necessary.
• Installation Complexity: Hot-applied asphalt and torch methods require skilled crews and safety precautions.
• Lower Reflectivity: Traditional BURs with gravel are less reflective unless topped with a reflective coating.
• Long Drying/Curing Times: Hot applied systems require time before the roof can be trafficked or coated.

Cost Considerations And Budgeting

Installation and lifecycle costs vary by region, roof complexity, and material choices. Typical installed costs range from $5.00 to $10.00 per square foot for new BUR systems, with overlays and coatings adding expense. Maintenance costs are modest but necessary for maximizing life expectancy.

Item	Estimated Cost
New BUR Installation	$5.00–$10.00 Per Sq Ft
Patching/Small Repair	$200–$1,000 Depending On Scope
Gravel Replacement Or Topcoat	$1.00–$3.00 Per Sq Ft

Inspection And Maintenance Best Practices

Regular inspection and timely maintenance are essential to prolong BUR service life. A roof maintenance plan should include at least two inspections per year plus after severe storms or heavy traffic events.

• Visual Inspections: Look for blisters, splits, loose gravel, ponding water, and compromised flashing.
• Drainage Checks: Ensure drains, scuppers, and gutters are clear to prevent ponding which accelerates deterioration.
• Flashings And Penetrations: Inspect flashings, curb seals, and rooftop units for leaks or degraded sealant.
• Periodic Recoating: Apply reflective coatings to extend life and reduce thermal cycling if applicable.

Repair Techniques For BUR

Repairs should match the original BUR type when possible. Patching requires removing damaged plies, applying new felts, and integrating bitumen to ensure a watertight repair.

• Small Patches: Cut clean edges around damage, apply primer, new ply layers, and finish with surfacing.
• Large Repairs: Remove affected area to sound substrate and reinstall plies with proper tapering to avoid ridges.
• Chemical/Cold Repairs: Use compatible cold adhesives or mastics where hot work is impractical.

When To Consider Replacement Or Upgrading

Replacement should be considered when recurring leaks, extensive ponding, or multiple failed plies compromise performance. If repair costs exceed 50% of a new roof or if structural issues exist, replacement is usually more cost-effective.

• Overlay Option: In some cases a single-ply or modified bitumen overlay can be installed over existing BUR to lower replacement cost.
• Transition To Reflective Systems: Upgrading to TPO or PVC may improve energy performance and reduce rooftop temperatures.

Code, Safety, And Environmental Considerations

BUR installations must comply with local building codes and fire regulations. Hot-applied asphalt and torch applications require permits and fire watch. Environmental concerns include volatile organic compounds, odor, and disposal of coal-tar residues.

• Permitting: Verify local code requirements for hot work and roof assemblies.
• Fire Safety: Implement fire watch protocols and use flame-retardant materials where mandated.
• Waste Disposal: Dispose of removed BUR materials per local hazardous-waste rules, particularly coal-tar products.

Choosing A Contractor And Specifying A BUR System

Select contractors with proven BUR experience, manufacturer training, and liability insurance. Request references, inspection reports for past work, and written warranties for materials and labor.

• Specification Tips: Specify number of plies, felt type, bitumen grade, surfacing, and flashing details in the contract.
• Warranties: Seek both manufacturer and installer warranties; typical labor warranties range from 1–10 years depending on contract terms.

Comparing BUR With Alternative Low-Slope Systems

BUR competes with modified bitumen, single-ply (TPO, PVC, EPDM), and metal roofing. BUR offers proven durability and redundancy, while single-ply systems often provide higher reflectivity and faster installation.

System	Strengths	Weaknesses
BUR	Durability, Redundancy, Fire Resistance	Weight, Installation Complexity, Lower Reflectivity
TPO/PVC	High Reflectivity, Lightweight, Faster Install	Seam Vulnerability, Material Compatibility Issues
Modified Bitumen	Good Flexibility, Easier Patching	Similar Weight, Some Heat Sensitivity

Key Takeaways For Property Managers And Owners

Asphalt built-up roofing remains a reliable choice for low-slope roofs when installed and maintained properly. Its multi-layer construction provides proven waterproofing and resilience, particularly for high-traffic rooftop areas. Consider surfacing upgrades and proactive maintenance to extend service life and improve energy performance.

Resources And Further Reading

Consult NRCA (National Roofing Contractors Association), state building codes, and material manufacturer technical data sheets for detailed specifications and installation guidance. Engaging a qualified roofing consultant early can optimize system selection and lifecycle costs.