The original multi-ply commercial roof, engineered for decades of punishing service
Built-up roofing, almost always shortened to BUR, is the original commercial low-slope roof system. Layers of asphalt-impregnated felt are alternated with hot-mopped asphalt, then topped with a protective flood coat and gravel ballast. The result is a monolithic, multi-ply membrane that has been proven on warehouses, schools, and institutional buildings for more than a century.
At National Restoration, we still specify and install BUR on projects where durability, redundancy, and fire rating are the first priorities. A properly installed gravel-surfaced BUR routinely delivers proven decades of service, and the top layer of stone protects the membrane from UV and foot traffic better than any single-ply system. For owners who want a roof they rarely have to think about, BUR remains one of the most dependable specifications in commercial roofing.
Newer single-ply systems get the marketing attention, but BUR continues to earn specification on the roofs where performance truly matters.
A standard BUR system includes three to four plies of reinforcing felt bonded in hot asphalt. If one ply is compromised, the others continue to function as a complete water-shedding layer.
Gravel-surfaced BUR carries the highest Class A fire rating and is frequently required on schools, hospitals, and other institutional buildings where exterior fire spread is a life-safety concern.
The gravel ballast protects the membrane from hail, debris, and foot traffic. BUR is the right call for roofs with frequent HVAC service, communications equipment, and rooftop penetrations.
The aggregate surface shields the asphalt below from UV degradation, the single greatest enemy of any asphalt roof. This is why original BUR installations from the 1960s and 70s are still performing.
With a proven long service life and minimal maintenance requirements, BUR delivers one of the lowest cost-per-year metrics in commercial roofing. Restoration coatings can extend the life further.
The multi-ply, hot-mopped assembly creates a continuous, seamless membrane with no heat-welded or taped seams. It is arguably the most watertight commercial roof assembly ever developed.
We engineer each BUR assembly to the building's specific requirements, from ply count and surfacing to insulation thickness and attachment method.
The traditional specification. Four plies of felt are hot-mopped together and finished with a flood coat of asphalt embedded with 400 pounds of gravel per square.
Instead of gravel, the flood coat is topped with a cap sheet or left smooth and coated with an aluminized asphalt coating. Lighter in weight and easier to inspect than gravel systems.
A granulated mineral-surfaced cap sheet replaces the gravel ballast, combining the redundancy of traditional BUR with a more modern finished appearance.
We tailor the ply count and bitumen type to the warranty and performance required.
Hot-applied BUR is a high-skill installation. Every project is led by a foreman with years of specific BUR experience and backed by strict kettle and fire-watch protocols.
The existing roof is removed, deteriorated decking is replaced, and a clean substrate is established. On re-roofs, we perform moisture scans to identify and replace wet insulation.
A vapor retarder is installed where required, followed by layered polyiso insulation that brings the assembly to current code R-values. Cover board is installed to provide a hot-asphalt-compatible substrate.
The base sheet is mechanically attached or mopped down, then successive plies of Type IV or Type VI fiberglass felt are rolled into hot asphalt with careful overlap sequencing to create the multi-layer assembly.
A flood coat of hot asphalt is applied over the completed plies, providing the matrix that holds the gravel ballast and seals the top of the membrane against water intrusion.
Smooth or crushed stone is embedded in the flood coat at 400-500 pounds per square, creating the UV shield and impact protection that gives BUR its legendary service life.
Multi-ply bitumen flashings are built up at every parapet, curb, and penetration, and metal counter-flashings are installed where the specification requires. The completed roof is inspected ply by ply before sign-off.
With minimal routine care, a built-up roof can easily exceed its warranty period. Our maintenance programs are designed around the specific wear points of BUR systems.
Annual Inspection & Clearing
We remove debris, clear drains and scuppers of ballast migration, and inspect flashings and counter-flashings for wear or displacement
Flashing & Detail Repair
The most common BUR service issue is at flashings, not the field. Small separations are rebuilt with new bitumen plies on the spot
Restoration Coatings
Aged smooth or cap-sheet BUR can be cleaned and top-coated with aluminum, silicone, or acrylic roof coatings that meaningfully extend service life and improve energy performance
When your roof has to work hard, BUR still earns its place on the spec sheet. We install gravel, smooth, and cap-sheet built-up systems engineered for decades of service. Schedule your rooftop evaluation.