Built up roof systems, commonly referred to as BUR, are a longstanding solution for flat and low-slope roofs in the United States. This article explains how BUR works, its main components, advantages and drawbacks, installation steps, and maintenance considerations. It also covers safety, code considerations, and tips for selecting a qualified contractor. Understanding these aspects helps building owners compare BUR with other roofing options and plan durable, cost-effective roof assemblies.
Overview Of Built Up Roof Systems
What it is A built up roof is a multilayer assembly that combines alternating layers of asphalt or coal tar pitches and reinforcing fabrics, topped with a protective surface. Classic BURs typically incorporate 3 to 5 plies, with a granule- or reflective-surfaced cap sheet. The finished roof forms a seamless, watertight membrane that protects interior spaces from moisture, weather, and temperature fluctuations.
Where it’s used BUR is favored for commercial buildings, schools, warehouses, and multifamily housing with flat or low-slope roofs. Its durability, proven track record, and versatility in roof deviations, curbs, and penetrations contribute to long service life in diverse climates.
How A BUR System Works
A BUR system relies on multiple reinforcing plies bonded with waterproofing asphalt, pitch, or bitumen. Each ply adds redundancy, improving puncture resistance and seam integrity. The top surface, often mineral granules or reflective coating, shields the membrane from UV damage and weathering. When properly installed, the layers shed water and resist wind uplift, even under heavy rain, hail, or temperature swings.
Critical to performance are proper surface preparation, ply orientation, and adhesion. Cold-applied or hot-applied asphalt is used to bond plies, and some modern BURs may incorporate a polymer-modified asphalt to enhance elasticity and flexibility in cold weather. The final cap sheet provides UV protection, weather resistance, and a suitable finish for maintenance access paths or ballast integration.
Key Components Of A Built Up Roof
- Substrate usually structural deck or insulation board providing a stable base.
- Waterproofing Plies multiple layers of reinforcing fabric embedded in hot or cold asphalt or coal tar pitch.
- Base Layer first ply that adheres directly to the deck, establishing the primary waterproof barrier.
- Middle Plies additional fabric plies that add strength and redundancy.
- Cap Sheet top layer featuring mineral granules or a reflective coating to resist UV exposure and weathering.
- Surface Finish granules, reflective coatings, or ballast (gravel or paver stones) to protect against sun and wind uplift and to distribute weight evenly.
Pros And Cons Of Built Up Roofs
- Durability Excellent puncture resistance and long service life with proper maintenance.
- Weather Resistance Good in diverse climates; multilayer design provides redundancy against leaks.
- Cost Moderate initial cost; long-term cost-effective due to longevity and repairability.
- Maintenance Requires periodic inspection to address seams, flashings, and ballast adjustments.
- Weight Heavier system; structural considerations needed for retrofit projects.
- Construction Time Installation can be time-consuming, especially for larger or complex roof geometries.
Installation Process For A BUR System
The BUR installation involves several coordinated steps to ensure a durable roof. Preparation includes inspecting the deck, repairing damage, and ensuring a clean substrate. The process typically follows:
- Deck preparation and moisture mitigation.
- Application of the adhesive base ply and embedding in hot asphalt or cold process
- Layering additional plies in a crisscross or aligned orientation to maximize strength
- Install cap sheet, followed by surface finish such as granules or reflective coating
- Ballast placement, if used, for wind uplift resistance and additional protection
Certain BUR configurations use self-adhesive or heat-welded membranes, especially in regions with extreme temperatures or high wind exposure. Contractors must adhere to manufacturer guidelines and local building codes to ensure warranty validity and safety compliance.
Maintenance And Repairs
Regular inspections are essential to extend BUR life. Focus on:
- Seams And Flashings Look for cracks, edge separations, or loose flashings around chimneys, vents, and skylights.
- Cap Sheet Check for punctures, blistering, or degradation of surface granules.
- Water Stains Inspect interior ceilings and walls for signs of moisture that indicate hidden leaks.
- Drainage Systems Ensure gutters and scuppers are clear to prevent ponding.
- Expansion Joints Verify that joints accommodate building movement without compromising waterproofing.
Repairs typically involve removing damaged sections, resealing seams, or applying new plies with compatible asphalt. For extensive damage, a partial or full roof replacement may be more cost-effective in the long run. DIY patches should be avoided as they can disrupt the integrity of multiple plies and void warranties.
Safety, Codes, And Environmental Considerations
Safety protocols are critical due to height, fall hazards, hot asphalt processes, and heavy materials. Contractors should follow OSHA guidelines, provide fall protection, and use proper PPE. Building codes govern BUR installation specifics, including nailing patterns, vapor barriers, and fire resistance ratings.
Environmental considerations include material recycling options, ballast management in ballast BUR installations, and the potential for reflective coatings to reduce urban heat island effects. Polymer-modified asphalt formulations may offer improved performance and energy efficiency in hot climates.
Choosing A Contractor For A Built Up Roof Project
Selecting a qualified contractor is crucial for BUR performance and warranty protection. Consider these criteria:
- Experience Proven track record with BUR installations on similar building types and climates.
- Licensing And Insurance Ensure proper licensing, workers’ compensation, and liability coverage.
- Warranty Clear materials and workmanship warranties specifying coverage and duration.
- References Request and check recent project references and site visits.
- Manufacturer Certifications Verify that installers are certified or trained by the roof membrane manufacturers.
Before committing, obtain multiple written bids that detail materials, installation methods, schedule, and post-installation maintenance requirements. A well-planned BUR project minimizes downtime and ensures long-term performance.