Built-Up Smooth Roof: Guide to Materials, Installation, and Maintenance

Built-Up Smooth Roof refers to a traditional membrane roofing system often used on low-slope commercial and residential buildings that emphasizes a smooth, uniform finished surface.

Feature	Built-Up Smooth Roof
Primary Materials	Asphalt, felt layers, surfacing (smooth cap sheet or coating)
Typical Lifespan	20–35 Years With Proper Maintenance
Common Uses	Low-slope commercial roofs, residential flat roofs, garages
Advantages	Durability, multi-layer redundancy, smooth waterproof finish
Considerations	Weight, installation labor, maintenance needs

Introduction: A built-up smooth roof (BUR) is a multi-ply assembly combining bitumen and reinforcing felts with a smooth surfacing layer to create a continuous, weatherproof roof membrane. This guide explains materials, installation steps, advantages, costs, maintenance, and troubleshooting to help building owners make informed decisions about BUR systems.

What Is A Built-Up Smooth Roof?

A built-up smooth roof is a traditional roofing membrane assembled from alternating layers of asphalt or coal tar and roofing felts, finished with a smooth surfacing such as a cap sheet, mineral-surfaced membrane, or coating. Its defining trait is the smooth, continuous top layer that provides waterproofing and UV protection.

Core Materials And Components

BUR systems use a set of standard components selected for compatibility and performance. Understanding these materials helps predict durability and maintenance needs.

Bitumen (Asphalt Or Coal Tar)

Bitumen acts as the adhesive and waterproofing agent between felts. Asphalt is most common today due to availability and environmental regulations, while coal tar was used historically for chemical resistance.

Roofing Felts

Felts (organic or fiberglass) provide reinforcement. Modern systems favor fiberglass felts for better dimensional stability and fire resistance. Multiple plies increase redundancy and puncture resistance.

Smooth Surfacing

Surfacing options include smooth cap sheets, elastomeric coatings, or poured/embedded finished layers. These deliver the characteristic smooth appearance and protect the plies from UV and weathering.

Installation Process And Best Practices

BUR installation is labor-intensive and requires skilled crews. Proper deck preparation, ply adhesion, and surfacing application are critical for long-term performance.

Deck Preparation

The roof deck must be clean, dry, and structurally sound. Insulation and vapor barriers are installed per code. Any deck irregularities should be corrected to ensure a flat substrate for the BUR system.

Ply Application

Plys are embedded in hot or cold-applied bitumen in a specified sequence. Overlaps and securement follow manufacturer and local building code requirements. Quality control during ply laying minimizes blistering, wrinkles, and cold joints.

Smooth Cap Or Coating Application

The final surfacing—smooth cap sheet or coating—must be applied uniformly. Coatings require specific temperatures and curing conditions. Proper flashing at penetrations ensures a continuous waterproof barrier.

Advantages Of Built-Up Smooth Roofs

BUR systems remain popular for several reasons. Their multi-layer construction provides robust waterproofing and redundancy that single-ply systems may lack.

• High puncture and impact resistance due to multiple felts.
• Good UV protection when paired with reflective coatings.
• Proven track record on low-slope buildings.
• Customizable surfacing for aesthetics and slip resistance.

Limitations And Considerations

While durable, BUR systems present trade-offs. Weight, installation complexity, and potential for seam-related issues require evaluation.

• Heavier than most single-ply membranes—structural capacity must be confirmed.
• Installation is labor- and time-intensive, increasing upfront costs.
• Hot-applied systems pose fire risk and require experienced crews.
• Older coal-tar systems may contain hazardous materials needing specialized remediation.

Cost Factors And Budgeting

The cost of a built-up smooth roof varies by region, roof size, number of plies, insulation, and surfacing choice. Budget calculations should include removal of existing roof, roof deck repairs, insulation, and long-term maintenance.

Typical installed costs tend to be higher than single-ply options but lower than some specialty systems when measured on an installed-dollar-per-square-foot basis for multi-ply durability.

Maintenance Practices For Longevity

Routine maintenance extends the life of a BUR system. A proactive maintenance program identifies and repairs issues before they escalate.

• Perform biannual inspections and after severe weather events.
• Clear drains and scuppers to prevent ponding water.
• Promptly repair blisters, splits, and seam failures with compatible materials.
• Recoat or reseal surfacing as specified by the coating manufacturer to restore UV protection.

Common Problems And How To Fix Them

BUR roof issues typically stem from ponding, mechanical damage, or aging. Targeted repairs can restore watertight integrity without full replacement in many cases.

Blisters And Delamination

These occur when trapped moisture or vapor expands under the plies. Repairs include cutting out and patching affected areas and addressing vapor drive with installation of vapor barriers during replacement.

Ponding Water

Ponding accelerates deterioration. Solutions include improving roof slope with tapered insulation or installing additional drains and scuppers. Design changes are often required for persistent ponding.

Seam Failures And Flashing Issues

Seams and flashings are vulnerable points. Re-soldering, re-bonding, or overlaying with compatible membranes and coatings restores continuity. Proper flashing details prevent recurring leaks around penetrations.

Comparing Built-Up Smooth Roofs To Alternatives

When choosing a roofing system, comparison to single-ply (TPO, PVC, EPDM) and modified bitumen systems is essential. Each system offers distinct advantages depending on budget, structure, and performance requirements.

Aspect	Built-Up Smooth Roof	Single-Ply (TPO/EPDM)
Durability	High with multiple plies	Variable; depends on membrane
Weight	Heavier	Lighter
Installation Speed	Slower, more labor	Faster
Repairability	Good; local patches effective	Good; seam repairs common

Energy And Environmental Considerations

Built-up smooth roofs can contribute to energy efficiency when paired with reflective surfacings or cool coatings. Reflective finishes reduce heat gain and lower HVAC loads in warm climates.

Recycling options for removed BUR materials are limited but improving; some components can be reclaimed or processed as roof tear-off recycling advances.

When To Replace Versus Repair

Decision-making depends on extent of damage, age, and lifecycle cost. Large-area rot, multiple recurring leaks, or end-of-service-life indicators typically trigger replacement.

Spot repairs suit isolated defects. A professional roof assessment including moisture scanning helps determine whether overlay, partial replacement, or full roof replacement is most cost-effective.

Selecting A Contractor And Warranty Tips

Choosing an experienced roofing contractor ensures proper BUR installation and longevity. Verify manufacturer-authorized applicators, licensing, insurance, and local references.

• Request detailed proposals with layer counts, materials, and warranty specifics.
• Confirm that labor and material warranties are provided in writing.
• Consider maintenance agreements to preserve warranties and system performance.

Frequently Asked Questions

How Long Does A Built-Up Smooth Roof Last?

With proper installation and maintenance, a BUR system commonly lasts 20 to 35 years, though lifespans vary based on materials and climate.

Can A BUR Be Installed Over An Existing Roof?

In some jurisdictions, BUR systems may be installed as overlays if the deck supports additional weight and the existing roof is compatible. Local codes and structural assessments dictate overlay feasibility.

Are Built-Up Smooth Roofs Energy Efficient?

Yes. When equipped with reflective or cool coatings, BUR roofs reduce solar heat absorption and can lower cooling energy use during hot seasons.

Key Takeaways For Building Owners

Built-up smooth roofs offer durable, multi-layer protection ideally suited to low-slope applications, balancing longevity and repairability against weight and installation complexity. A well-chosen BUR system with routine maintenance can deliver decades of reliable service and good energy performance when finished with the appropriate surfacing.