What Is a Built-Up Roof: Complete Guide to BUR Systems

Built-up roofing (BUR) is a traditional, multi-layer roofing system widely used on low-slope commercial and residential buildings across the United States. This guide explains what a built-up roof is, how BUR systems are constructed, their advantages and limitations, maintenance needs, and cost considerations to help readers make informed decisions.

Topic	Key Points
Definition	Layered Asphalt And Felts
Best Use	Low-Slope Commercial Roofs
Longevity	20–40 Years With Proper Maintenance
Common Materials	Asphalt, Coal Tar, Fiberglass/Organic Felts, Gravel

What Is A Built-Up Roof (BUR)?

A built-up roof, often abbreviated BUR, is a multi-ply roofing system assembled on-site using alternating layers of bitumen (asphalt or coal tar) and reinforcing fabrics called felts or mats. The top surface is typically finished with gravel, stone, or a reflective coating. BUR Systems Create A Durable, Watertight Membrane Suitable For Low-Slope Roofs.

History And Evolution Of Built-Up Roofing

Built-up roofing dates to the mid-19th century and became the dominant low-slope roofing method for commercial buildings across the 20th century. Originally using coal tar, the industry transitioned to asphalt and modified bitumens for improved performance and reduced odor. BUR Has Evolved With Better Materials And Installation Techniques But Retains Its Core Multi-Ply Design.

Components Of A Built-Up Roof

Understanding BUR requires knowing the main components: the roof deck, insulation, bitumen, roofing felts, and surfacing. Each component contributes to weatherproofing, thermal performance, and structural compatibility. Each Layer Performs A Specific Function In The Roof Assembly From Structural Support To UV Protection.

Roof Deck And Insulation

The deck can be concrete, steel, or wood; insulation is installed to meet thermal code requirements and improve energy efficiency. Proper Insulation Prevents Thermal Shock And Reduces Energy Costs While Supporting The BUR Layers.

Bitumen Types

Bitumen may be asphalt-based or coal-tar-based, and sometimes consist of modified asphalt blends. Choice depends on performance needs, environmental constraints, and local code. Asphalt Is Most Common Today For Its Balance Of Cost And Performance.

Roofing Felts And Reinforcements

Felts are typically fiberglass or organic cellulose mats saturated with bitumen to reinforce the membrane. Multiple plies increase redundancy and puncture resistance. Fiberglass Felts Offer Greater Dimensional Stability And Rot Resistance Compared With Organic Felts.

Surfacing Options

Gravel or stone ballast is common to protect against UV and physical damage; alternatively, reflective coatings or pavers can be used for energy performance and aesthetics. Gravel Surfacing Adds Weight But Extends UV Protection.

Installation Methods

Built-up roofs are installed using several methods depending on materials and job conditions: hot mopping with kettles, cold adhesives, torched application for some components, or mechanically fastened systems. Choice Of Installation Affects Safety, Cost, And Long-Term Performance.

Hot Mop Installation

Hot mopping melts bitumen in kettles and spreads it between felt plies. It creates strong adhesion and continuity but requires skilled crews and strict safety precautions. Hot Mopping Is Traditional And Highly Reliable When Properly Done.

Cold Adhesive Systems

Cold-applied adhesives reduce fire risk and odors, often using solvent or solvent-free adhesives to bond felts. This method is safer in occupied buildings and can be more environmentally friendly. Cold Systems Minimize Open-Heat Hazards.

Torch-Applied And Mechanically Fastened Options

Torch-applied felts use open flame to bond asphalt sheets; mechanically attached systems secure insulation and plies with fasteners. Both methods are used selectively based on substrate and accessibility. Each Method Requires Trained Installers To Avoid Installation Failures.

Benefits Of Built-Up Roofs

Built-up roofs offer strong puncture and wear resistance, redundancy through multiple plies, and long service life when maintained. They handle heavy pedestrian traffic and rooftop equipment well. BUR Provides A Cost-Effective, Durable Solution For Low-Slope Roofing Needs.

• Durability: Multiple layers resist leaks and impact.
• Cost-Effectiveness: Long lifespan offsets initial costs.
• Fire Resistance: Coal-tar BURs historically offered higher fire resistance.
• Maintenance Friendly: Repairs are typically straightforward for experienced roofers.

Limitations And Considerations

BUR systems are heavy and require structurally sound decks and proper drainage. Installation can be disruptive due to odors and hot equipment. Reflectivity and energy performance need attention without additional coatings. Weight, Installation Logistics, And Energy Concerns Should Guide Selection.

Weight And Structural Requirements

The weight of multiple plies plus gravel may require structural assessment of older buildings. Engineers commonly evaluate load capacity before BUR installation. Assessing Structural Capacity Prevents Long-Term Structural Issues.

Maintenance Needs

Routine inspections, gravel redistribution, flashings checks, and prompt repairs of ponding or membrane damage are essential to extend service life. Proactive Maintenance Can Add Decades To A BUR System.

Common Problems And How To Fix Them

Leaks at seams, flashing failures, ponding water, and membrane blisters are common BUR issues. Proper diagnosis leads to targeted repairs like patching, re-flashing, or adding tapered insulation. Timely Repairs Prevent Minor Issues From Becoming Costly Failures.

Seam Failures And Flashings

Seams are vulnerable if installation is poor or if thermal cycling causes movement. Replacing or reinforcing flashed areas often resolves recurring leaks. Quality Flashing Details Are Critical For Long-Term Leak Prevention.

Ponding Water

Ponding accelerates membrane degradation and promotes leaks. Solutions include improving drainage, adding tapered insulation, or installing additional drains. Eliminating Ponding Water Extends A Roof’s Lifespan.

Energy Performance And Sustainability

Traditional BUR with dark surfaces absorbs heat, increasing cooling loads. Applying reflective coatings or using light-colored surfacing reduces energy use. Re-roofing with insulated BUR assemblies improves thermal performance and meets modern codes. Reflective Coatings And Upgraded Insulation Improve Energy Efficiency.

Costs And Lifespan

Initial installation cost varies by materials, labor method, roof size, and local labor rates. Typical service life ranges from 20 to 40 years with proper maintenance; many factors influence longevity, including climate and maintenance frequency. Lifetime Costs Depend On Installation Quality And Ongoing Maintenance.

Cost Factor	Typical Range
Installation	Moderate To High (Depends On Method)
Annual Maintenance	Low To Moderate
Replacement Cycle	20–40 Years

Comparing BUR To Alternative Roof Systems

BUR competes with single-ply membranes (TPO, EPDM), modified bitumen, and metal roofing. Each system has trade-offs in cost, installation complexity, energy performance, and durability. Selection Should Be Based On Building Use, Slope, Budget, And Long-Term Goals.

• TPO/EPDM: Lightweight, reflective options with quicker installs.
• Modified Bitumen: Hybrid option with factory-finished sheets.
• Metal Roofing: Long lifespan but different thermal movement behavior.

Inspection And Maintenance Checklist

Regular inspections at least twice a year and after major storms help identify issues early. The checklist should cover surfacing, seams, flashings, drains, and rooftop equipment penetrations. Routine Inspections Are The Best Investment To Prolong BUR Life.

1. Check For Loose Gravel, Exposed Felts, And Surface Wear.
2. Inspect Flashings Around Penetrations And Parapets.
3. Ensure Drains Are Clear And Slope Is Adequate.
4. Document And Repair Any Blisters Or Punctures Promptly.

Hiring A Contractor And Warranty Considerations

Select a contractor with BUR experience, proper licensing, and references. Warranties vary: manufacturer warranties cover materials while workmanship warranties cover installation errors. Verify Warranty Terms And Get Written Guarantees Before Work Begins.

When To Consider Re-Roofing Or Upgrading

Signs that re-roofing is needed include frequent leaks, extensive membrane degradation, or inability to meet updated energy codes. Upgrading may involve adding insulation, switching to a reflective coating, or installing a new system. Strategic Upgrades Can Improve Energy Performance And Extend Roof Life.

Resources And Standards

Industry organizations such as the National Roofing Contractors Association (NRCA) and building codes provide installation guidance, specifications, and best practices for BUR systems. Consulting these resources helps ensure code compliance and performance. Follow NRCA Guidelines And Local Codes For Best Results.

For homeowners and building managers, understanding what a built-up roof is and how BUR systems perform enables smarter decisions when selecting, maintaining, or replacing low-slope roofing. Proper installation, regular maintenance, and attention to drainage and flashing details are the keys to maximizing the lifespan and value of a built-up roof.