What Is Built-Up Roofing?
Built-up roofing, commonly called BUR or "tar and gravel" roofing, is a multi-layered roofing system constructed by alternating layers of bitumen (asphalt or coal tar) and reinforcing fabrics called ply sheets. Each layer bonds to the one below it, creating a continuous, monolithic waterproofing membrane that grows stronger with each additional ply. The finished system is then topped with either aggregate (gravel) or a mineral-surfaced cap sheet to protect the bitumen from UV degradation.
A typical BUR system in Pinellas County consists of three to five plies of reinforcing fabric, each set in hot asphalt. This creates a total membrane thickness of roughly 150 to 300 mils, which is significantly thicker than a single-ply membrane like TPO (60 to 80 mils). That extra thickness provides exceptional puncture resistance, redundancy against leaks, and a level of ruggedness that has kept BUR relevant for over a century of commercial roofing.
The "built-up" name comes from the construction method itself. Rather than rolling out a single sheet of waterproofing, the roofer literally builds up the membrane one layer at a time. Each ply of reinforcing fabric (traditionally organic felt, now commonly fiberglass) is embedded in hot bitumen, creating a laminated assembly. If one layer develops a defect, the layers below continue to provide waterproofing protection, giving BUR an inherent redundancy that single-ply systems cannot match.
How Built-Up Roofing Is Constructed: Layer by Layer
Understanding BUR construction helps property owners evaluate contractor proposals and make informed decisions about their flat roof investment. Here is what goes into a properly constructed BUR system from bottom to top.
Layer 1: Roof Deck Preparation
The process begins with a clean, dry, structurally sound roof deck. In Pinellas County commercial buildings, this is typically a steel deck, concrete deck, or wood deck. Any existing roofing material is removed down to the structural deck unless the project is a recover installation. The deck must be inspected for damage, proper slope (minimum 1/4 inch per foot for drainage), and structural adequacy to support the BUR system weight.
Layer 2: Vapor Barrier
In Florida's humid climate, a vapor barrier is installed over the deck to prevent moisture from the building interior from migrating into the insulation and roofing layers. This is particularly important for refrigerated buildings, natatoriums, and any structure with high interior humidity. The vapor barrier is typically a self-adhering modified bitumen sheet or a mopped-in asphalt layer with a polyethylene film.
Layer 3: Insulation
Rigid roof insulation, typically polyisocyanurate (polyiso) board, is installed over the vapor barrier. Florida Energy Code requires minimum R-values for commercial roof assemblies, and the insulation layer is where these requirements are met. Insulation boards are typically installed in two staggered layers to minimize thermal bridging at board joints. Tapered insulation systems can also be used to create positive drainage slope on structurally flat decks.
Layer 4: Base Sheet
A base sheet is mechanically fastened or adhered to the top of the insulation. This fiberglass-reinforced sheet provides a stable foundation for the hot-mopped BUR plies and protects the insulation during the hot asphalt application process. Mechanical fastening of the base sheet is critical in Florida wind zones because it provides the primary attachment of the entire roof system to the structural deck.
Layers 5 through 7: Ply Sheets in Hot Asphalt
This is the heart of the BUR system. A crew member operates the kettle, heating asphalt to approximately 400 to 450 degrees Fahrenheit. The hot asphalt is pumped or carried to the roof in mop carts. Workers mop the hot asphalt onto the base sheet, then immediately roll fiberglass ply sheets into the hot asphalt before it cools. Each subsequent ply is set in its own layer of hot asphalt, building up the waterproofing membrane ply by ply.
A standard three-ply BUR system provides good waterproofing for most commercial applications. Four-ply and five-ply systems offer additional redundancy and are specified for critical facilities such as hospitals, data centers, or buildings where any roof leak would cause significant damage. The more plies in the system, the greater the puncture resistance and leak redundancy.
Layer 8: Surfacing (Gravel or Cap Sheet)
The final layer protects the BUR membrane from UV radiation, provides fire resistance, and adds an additional layer of protection. Building owners in Pinellas County typically choose between two surfacing options: aggregate gravel or mineral-surfaced cap sheet. Each option has distinct advantages that we explore in detail below.
Gravel vs Cap Sheet: Choosing Your BUR Surface
The surfacing choice for a BUR roof significantly impacts maintenance requirements, inspection ease, and storm performance. In Pinellas County, this decision carries additional weight due to hurricane and wind considerations.
Aggregate (Gravel) Surfacing
Traditional BUR surfacing uses a heavy flood coat of hot asphalt topped with a layer of opaque, light-colored gravel at a minimum rate of 400 pounds per 100 square feet. The gravel shields the asphalt from UV radiation, provides excellent fire resistance (Class A rating), and adds significant ballast weight that helps resist wind uplift. The aggregate also reflects sunlight better than dark asphalt, reducing roof surface temperatures.
However, gravel surfacing presents challenges in Florida. During hurricanes and severe tropical storms, loose gravel can become windborne projectiles, causing damage to neighboring buildings, vehicles, and the roof membrane itself. Insurance carriers in Pinellas County increasingly scrutinize gravel-surfaced roofs and may require removal of loose aggregate as a condition of coverage. Additionally, gravel makes roof inspections difficult because defects in the membrane are hidden beneath the aggregate layer.
Mineral-Surfaced Cap Sheet
Cap sheet surfacing uses a factory-manufactured modified bitumen sheet with ceramic mineral granules embedded in the top surface. The cap sheet is heat-mopped or torch-applied to the top BUR ply, creating a smooth, uniform surface that is easy to inspect and maintain. Cap sheet surfacing eliminates the windborne debris concern associated with gravel, making it the preferred BUR surfacing option for Pinellas County buildings in hurricane zones.
Cap sheet also allows for easier and more accurate roof inspections. Maintenance personnel can visually identify blisters, cracks, wrinkles, and other defects without clearing gravel away first. This visibility leads to earlier problem detection and more cost-effective repairs. White or light-colored cap sheets are available and can help meet Florida cool roof requirements for energy code compliance.
| Feature | Gravel Surfacing | Cap Sheet Surfacing |
|---|---|---|
| UV Protection | Excellent | Very Good |
| Fire Resistance | Class A | Class A (with proper system) |
| Wind Debris Risk | High (windborne gravel) | Low (no loose material) |
| Inspection Ease | Difficult (hidden defects) | Easy (visible surface) |
| Puncture Resistance | Excellent (stone protection) | Very Good |
| Foot Traffic Durability | Excellent | Good |
| Cool Roof Options | Light-colored aggregate | White/reflective cap sheet |
| FL Hurricane Zone Suitability | Problematic | Preferred |
Florida Heat Application Challenges for BUR
Installing built-up roofing in Florida presents unique challenges related to the hot application process. Understanding these challenges helps property owners appreciate why BUR installation requires experienced, skilled crews and careful project planning.
Asphalt Kettle Operations in Summer Heat
BUR installation requires heating asphalt to 400 to 450 degrees Fahrenheit in large kettles. During Pinellas County summers, ambient temperatures regularly exceed 95 degrees, and roof surface temperatures can surpass 150 degrees before any hot work begins. Working near a 450-degree kettle in these conditions creates extreme heat stress for crews. Most experienced BUR contractors in Florida schedule hot work during early morning hours (starting at 5:00 or 6:00 AM) and stop kettle operations by early afternoon to protect worker safety.
Fumes and Air Quality Concerns
Hot asphalt application produces visible fumes and strong odors that can affect building occupants, neighboring businesses, and the surrounding community. In Pinellas County's dense commercial areas, this is a significant consideration. Building owners should notify tenants and neighboring businesses before BUR installation begins. HVAC air intakes near the work area should be temporarily sealed or filtered to prevent fumes from entering the building interior. Some municipalities require advance notification or permits for hot asphalt roofing operations.
Rain Interruptions During Rainy Season
Florida's rainy season, which runs from approximately June through October, brings afternoon thunderstorms on a near-daily basis. BUR installation cannot proceed in wet conditions because moisture trapped between plies creates blisters and delamination. Each day's work must be fully completed and sealed before rain arrives. This makes BUR installation particularly schedule-sensitive during summer months in Pinellas County. A project that might take five days in winter can stretch to two or three weeks during rainy season due to weather delays.
Finding Skilled BUR Crews
As the commercial roofing industry has shifted toward single-ply membranes, the number of workers skilled in hot-applied BUR installation has declined. In the Tampa Bay and Pinellas County area, fewer roofing companies maintain the equipment and trained personnel needed for quality BUR work. This reduced availability can affect project scheduling and pricing. When evaluating BUR proposals, ask contractors about their crew experience with hot-applied systems and request references from recent BUR projects in Florida.
BUR Lifespan and Maintenance in Pinellas County
A well-installed BUR roof in Pinellas County can last 20 to 30 years with proper maintenance. Some high-quality installations have exceeded 40 years of service. The multi-layer construction provides built-in redundancy that allows BUR to continue performing even after minor damage occurs, unlike single-ply systems where a single puncture can cause an immediate leak.
Common BUR Maintenance Issues
Blistering is the most common BUR maintenance concern in Florida. Blisters form when moisture or air trapped between plies expands in the heat, pushing the top layers upward. Small blisters (under 6 inches) that are not in traffic areas can be monitored without immediate repair. Larger blisters or those in areas of foot traffic should be cut open, dried, re-mopped with hot asphalt, and patched to prevent further deterioration.
Alligatoring, a pattern of surface cracking that resembles alligator skin, indicates that the surface asphalt has oxidized and lost flexibility. This is primarily a cosmetic concern in early stages, but advanced alligatoring can allow water penetration into the ply system. Applying a roof coating over alligatored BUR can seal surface cracks, restore UV protection, and extend the roof's service life by 10 to 15 years.
Flashing failures at walls, curbs, and penetrations are another common maintenance need. BUR flashings are typically constructed from modified bitumen sheets installed over the base flashing detail. In Florida's heat, these flashings expand and contract daily, eventually developing cracks or separations at transitions. Semi-annual inspection and prompt repair of flashing details prevents water from entering the building through these vulnerable points.
BUR Maintenance Schedule for Florida
For Pinellas County BUR roofs, we recommend the following maintenance schedule to maximize roof lifespan and prevent costly repairs.
- Twice per year: Professional inspection of all flashings, seams, drains, and surface condition. Schedule before and after hurricane season.
- After every major storm: Visual inspection for debris damage, gravel displacement, ponding water, and flashing damage.
- Every 5 to 7 years: Consider applying a reflective roof coating to rejuvenate the surface and extend roof life.
- Every 10 to 15 years: Comprehensive condition assessment to determine remaining useful life and plan for eventual replacement.
Built-Up Roofing Cost in Pinellas County (2026)
BUR installation costs in Pinellas County reflect the labor-intensive nature of hot-applied construction. While material costs are moderate, the specialized equipment, skilled labor, and weather-dependent scheduling make BUR installations generally more expensive per square foot than single-ply alternatives. Here is a detailed cost breakdown for a typical commercial flat roof project.
| Cost Component | Cost Per Sq Ft | Notes |
|---|---|---|
| Tear-off and disposal | $1.50 to $3.00 | BUR tear-off is heavier than single-ply |
| Insulation (polyiso) | $1.50 to $3.00 | Varies by R-value needed |
| BUR membrane (3-ply) | $2.00 to $3.00 | Material including asphalt |
| Surfacing (gravel or cap sheet) | $0.75 to $1.50 | Cap sheet costs slightly more |
| Labor | $3.00 to $4.50 | Higher than single-ply due to complexity |
| Total Installed | $7.00 to $12.00 | Complete system with warranty |
For a 10,000 square foot commercial building in Pinellas County, a complete BUR roof replacement typically costs between $70,000 and $120,000. This is generally 10 to 25 percent more than a comparable TPO installation, primarily due to the higher labor costs associated with hot asphalt application. However, the cost-per-year calculation may favor BUR when its longer potential lifespan and superior puncture resistance are factored into the equation.
When Built-Up Roofing Still Makes Sense in 2026
Despite the growth of single-ply roofing systems, BUR remains the right choice for certain Pinellas County commercial buildings and situations. Here are the scenarios where BUR delivers advantages that justify its higher installation cost.
Heavy Foot Traffic Areas
Buildings with frequent rooftop access for HVAC maintenance, antenna servicing, or equipment operations benefit from BUR's exceptional puncture resistance and durability under foot traffic. The multi-layer construction and gravel or cap sheet surfacing provide a robust surface that withstands repeated foot traffic, tool drops, and equipment movement without the vulnerability of a thin single-ply membrane. Hospitals, hotels, and telecommunications facilities are common examples.
Buildings Requiring Maximum Redundancy
For critical facilities where any roof leak would cause severe damage, BUR's multi-layer redundancy provides an extra margin of safety. Data centers, archives, museums, medical facilities, and buildings housing sensitive electronics or inventory can justify BUR's higher cost for the peace of mind that multiple waterproofing layers provide. If a single ply is punctured, the remaining plies continue to keep water out.
Recovering Over Existing BUR
When a building already has a BUR roof that needs replacement, installing a new BUR system over the existing one (after removing the gravel surface) is often the most cost-effective approach. The new BUR bonds well to the existing asphalt surface, and the combined system creates an exceptionally thick, durable waterproofing assembly. This recover approach avoids the costly and disruptive tear-off of the heavy existing BUR system.
Buildings Where Aesthetics Do Not Matter
BUR is not a pretty roofing system. The gravel surface or dark cap sheet does not have the clean, uniform appearance of a white single-ply membrane. For industrial buildings, warehouses, and commercial properties where the roof is not visible from ground level or adjacent buildings, the appearance is irrelevant. In these cases, BUR's functional advantages can be prioritized without aesthetic compromise.
BUR vs Single-Ply Membranes: Complete Comparison
To help Pinellas County building owners make an informed decision, here is a comprehensive comparison of built-up roofing against the two most common single-ply alternatives.
| Factor | BUR (3-Ply) | TPO | EPDM |
|---|---|---|---|
| Installed Cost | $7.00 to $12.00/sq ft | $6.50 to $10.00/sq ft | $5.50 to $9.00/sq ft |
| Expected Lifespan | 20 to 30+ years | 20 to 30 years | 20 to 30 years |
| Puncture Resistance | Excellent (multi-layer) | Good | Good |
| Installation Speed | Slow (weather dependent) | Fast | Moderate to Fast |
| Leak Redundancy | High (multiple plies) | Low (single layer) | Low (single layer) |
| Energy Efficiency | Moderate (with white cap sheet) | High (reflective white) | Low to Moderate |
| Installation Fumes | Significant | Minimal | Moderate (adhesive) |
| Repair Complexity | Moderate | Moderate (heat welder) | Easy (patch and adhesive) |
Frequently Asked Questions About Built-Up Roofing
How long does a built-up roof last in Florida?
A properly installed built-up roof in Florida typically lasts 20 to 30 years. In Pinellas County, regular maintenance including re-coating the flood coat and addressing gravel displacement after storms can help BUR systems reach the upper end of their expected lifespan.
Is built-up roofing cheaper than TPO?
Built-up roofing is generally comparable to or slightly more expensive than TPO when fully installed. BUR materials are affordable, but the labor-intensive hot application process drives installation costs higher. A typical BUR installation in Pinellas County costs $7.00 to $12.00 per square foot, while TPO ranges from $6.50 to $10.00 per square foot.
What is the difference between gravel and cap sheet on a BUR roof?
Gravel surfacing uses a flood coat of hot asphalt covered with aggregate stone, providing UV protection, fire resistance, and ballast weight. Cap sheet surfacing uses a factory-made mineral-surfaced sheet heat-mopped to the top ply, creating a smoother surface that is easier to inspect and maintain. In Florida hurricane zones, cap sheet is often preferred because gravel can become windborne debris.
Can you walk on a built-up roof?
Yes, built-up roofs are among the most walkable commercial roofing systems. The multiple layers of reinforcement and the gravel or cap sheet surface provide excellent puncture resistance and traction. BUR is a preferred choice for buildings with heavy rooftop foot traffic from maintenance personnel, HVAC technicians, and equipment servicing.
Does BUR roofing still make sense in 2026?
Yes, BUR roofing remains a viable choice for specific applications in 2026. Buildings that require exceptional puncture resistance, heavy foot traffic durability, or are recovering over an existing BUR system can benefit from this time-tested technology. However, for new construction in Pinellas County, single-ply membranes like TPO often provide comparable performance at lower installed cost with faster installation.
Get Expert BUR Roofing Advice in Pinellas County
Built-up roofing has stood the test of time for over 150 years, and it continues to serve Pinellas County commercial buildings that demand maximum durability and puncture resistance. Whether you are considering a new BUR installation, need maintenance on an existing tar and gravel roof, or want to compare BUR against modern single-ply alternatives, a qualified local roofing contractor can help you make the right decision for your building and budget.
Browse our complete roofing guide for more information on all commercial roofing options, or explore our flat roof guide and flat roof cost breakdown for detailed comparisons that help you choose the best system for your Pinellas County property.