Hot tar roofing, also known as Hot Applied Built-Up Roofing (BUR), is one of the most durable and reliable commercial roofing systems available today. At Delta Innovative Services, we have decades of experience installing, maintaining, and restoring commercial roofs throughout the Midwest. Few systems match the stability, longevity, and proven performance of a properly engineered BUR assembly.
The Chemical Engineering Behind Hot Tar Roofing
Hot tar roofing is built on asphaltic bitumen, a refined petroleum product engineered through distillation and oxidation. Even though “hot tar” is the familiar term, roofing asphalt is scientifically designed to withstand extreme temperatures, UV exposure, and structural stress.
How Raw Asphalt Becomes Roofing-Grade Material?
Manufacturers convert raw asphalt into roofing-grade material by heating it to around 500 degrees Fahrenheit and injecting air into the mixture. This air blowing process adjusts hardness, viscosity, and softening point. The result is a more stable asphalt that resists flow on low-slope roofs, even under intense solar heat.
This refinement process produces asphalt that meets ASTM D312, the industry standard governing roofing asphalt performance. Each asphalt grade has required specifications for softening point, penetration, ductility, and flash point. For example, ASTM D312 mandates a minimum flash point of 575 degrees Fahrenheit, ensuring safe working conditions during application.
Polymer Modification for Enhanced Performance
Certain BUR systems integrate polymers such as SBS (Styrene Butadiene Styrene) or APP (Atactic Polypropylene) to improve flexibility and resistance to cracking.
- SBS adds rubber-like elasticity, helping prevent cold-weather fractures.
- APP improves high temperature stability and weldability.
These modified systems offer improved performance in regions with wide temperature swings or harsher environmental conditions.
The Multi-Ply Design: Why BUR Roofing Provides Extra Redundancy
The true strength of hot tar roofing lies in its engineered layering. BUR systems use alternating layers of asphalt and reinforcement plies to create a unified, high-performance waterproof membrane.
Components That Make BUR Strong
A BUR system begins with base sheets installed over the roof deck or insulation. In some assemblies, a slip sheet such as rosin paper is added first to prevent stress transfer from wood decks that naturally expand and contract.
Above the base sheet, installers embed multiple fiberglass reinforcement felts into the hot asphalt. Fiberglass is the preferred material because of its:
- High tensile strength
- Moisture resistance
- Dimensional stability
These reinforcement sheets form the structural backbone of the roof.
Why Redundancy Matters for Long-Term Waterproofing?
Unlike single-ply systems that rely on one membrane, BUR systems use three to five separate plies, each acting as its own waterproofing layer.
Every ply is fully adhered using calibrated amounts of hot asphalt, creating a composite system that significantly reduces the risk of leaks. For water to penetrate the building, it would need to breach each independent ply, making failure far less likely.
This multilayer redundancy explains why BUR roofs often remain watertight for 30 to 40 years or more.
Thermodynamic Precision: The Important Role of Temperature Control
The performance of a hot tar roofing system depends heavily on the accuracy of its installation. Proper viscosity, temperature control, and application technique are essential to achieving strong interply adhesion.
Understanding Equiviscous Temperature (EVT)
The most critical installation standard for BUR is the Equiviscous Temperature, or EVT. EVT represents the temperature at which asphalt reaches its ideal viscosity for bonding. Most asphalts achieve this between 355 and 420 degrees Fahrenheit.
- For mop application, the ideal viscosity is 125 cP
- For mechanical spreaders, it is 75 cP
Installers must keep asphalt within plus or minus 25 degrees of EVT during application. Asphalt that is too cool will not bond. Asphalt that is overheated becomes too thin and deteriorates faster.
Thermal Limits That Protect Material Integrity
Two crucial upper temperature limits must also be monitored:
- Flash Point: The temperature at which asphalt vapors can ignite
- Finished Blowing Temperature (FBT): The point above which asphalt begins to degrade chemically
Exceeding these temperatures for extended periods can damage the material and shorten the roof’s lifespan. This is why Delta Innovative Services follows strict temperature control protocols for every BUR installation.
How Hot Tar Roofing Performs in Real Weather Conditions?
Commercial roofs are constantly exposed to UV radiation, moisture, thermal expansion, and mechanical stresses. BUR systems are designed to withstand these environmental pressures better than many modern alternatives.
UV Protection Through Proper Surfacing
Asphalt degrades when exposed directly to UV light. BUR systems prevent this degradation using one of the following surfacing options:
- A flood coat of asphalt with embedded gravel
- A mineral-surfaced cap sheet
- A reflective coating applied over a smooth BUR system
Gravel is the most traditional and offers excellent impact resistance. Reflective coatings improve energy efficiency by reducing heat absorption.
Preventing Blistering Through Quality Installation
Blistering happens when trapped air or moisture expands under heat. The best prevention is proper installation with:
- Fully dry materials
- Complete asphalt coverage
- Venting base sheets when needed
These steps greatly reduce the likelihood of air pockets that can cause blisters.
Strong Resistance to Thermal Splitting
Temperature fluctuations cause roofing materials to expand and contract. If a membrane cannot absorb these stresses, cracks can develop.
BUR’s fiberglass reinforcement plies and optional SBS modification give the system:
- High tensile strength
- Excellent flexibility
- The ability to distribute stress without fracturing
This makes BUR especially suitable for climates with significant seasonal temperature variation.
How BUR Compares to Commercial Roofing Alternatives?
Although newer roofing technologies have become popular, BUR remains unmatched for its redundancy, fire resistance, and long-term durability.
BUR Versus Modified Bitumen Systems
Modified bitumen systems are essentially two-ply versions of BUR enhanced with polymers. While they offer flexibility and easier installation, they do not match the multilayer redundancy of a true BUR assembly. Additionally, torch-applied modified bitumen introduces open flame hazards during installation.
BUR Versus Cold-Applied and Liquid-Applied Systems
Cold-applied roofing systems eliminate the need for hot kettles and simplify future recoating. However, they rely on chemical curing, which is sensitive to weather and substrate conditions.
BUR systems cure through controlled cooling, which provides immediate adhesion and consistent performance regardless of ambient humidity.
For buildings that demand durability, impact resistance, and long-term reliability, BUR stands out as a top-tier choice.
The Value of True Roofing Engineering
Hot tar roofing is more than just a traditional technique. It is a scientifically engineered system grounded in material chemistry, thermodynamic precision, and a multilayer design that outperforms many modern alternatives. When installed correctly, a BUR roof offers some of the best long-term value in commercial roofing.
At Delta Innovative Services, our expertise ensures your building receives a top-quality system engineered for decades of performance.
Why Kansas City Chooses Delta Innovative Services for Long-Lasting Roofing Solutions
Contact Delta Innovative Services today to schedule a consultation. With decades of experience serving Kansas City businesses, we understand the unique climate demands and performance requirements of commercial roofs in this region. Our team is committed to delivering industry-leading craftsmanship, rigorous quality control, and long-term value on every project. Whether you need a full system replacement, a detailed assessment, or expert guidance on material selection, Delta Innovative Services is ready to protect your building with a roof built to last.