Commercial asphalt roofing has undergone a massive shift over the last few decades. Today, commercial property owners aren’t really choosing between a traditional built-up roof and a modified bitumen system. In fact, if you are a fan of BUR, we have bad news. Traditional built-up roofing is a thing of the past.
To make the most informed choice for your property, it helps to understand what commercial asphalt roofing used to be, what it has evolved into, and why the market has shifted toward modern single-ply membranes.
What Built-Up Roofing Was
Built-up roofing (BUR) is the oldest type of low-slope roofing system. For decades, it was the industry standard, relying on a thick, multi-layer construction built entirely on-site.
The installation followed a strict, laborious to-do list:
- Workers started with a roof deck made of concrete or wood.
- Installers applied alternating layers of hot bitumen (asphalt or coal tar pitch) and fiberglass ply felts, typically building up four separate layers.
- To protect the underlying layers from ultraviolet rays, pea-sized gravel was embedded into a final thick flood coat of hot asphalt.
While BUR provided excellent redundancy, meaning a leak had to penetrate multiple layers to cause damage, the industry has completely moved away from it. It is laborious to install, requires ongoing flashing maintenance, and creates safety hazards and harmful odors due to the hot asphalt kettles required on-site.
The Evolution into Modified Bitumen
To address the downsides of BUR, manufacturers developed modified bitumen (mod bit). Instead of building the entire roof layer-by-layer on a hot job site, mod bit asphalt is blended with specialized polymers in a factory and rolled out in uniform sheets. This factory-controlled manufacturing process eliminates human error and on-site variability.
Mod bit is generally installed as a quicker two-ply system. The installation relies on a clear distinction between these two critical layers:
- Smooth Base Plies: The bottom foundation layer always consists of completely smooth sheets.
- Granulated Cap Sheets: The top weathering layer features a factory-applied mineral granule surface. This design applies to both SBS and APP because both types of modified asphalt absolutely require protection from UV rays to prevent premature degradation. If a smooth sheet is ever mistakenly used as the final cap sheet, it must be coated on-site with silicone or another protective coating to shield it from sun damage.
When looking at mod bit options, the industry split into two primary polymer blends:
- APP (Atactic Polypropylene): This is a plastic-based modified asphalt. It features a high melting point and performs exceptionally well in hot climates. Because of its advanced performance and durability, APP is considered a premium product and carries a more expensive price tag. It is applied using roofing torches or cold-process adhesives.
- SBS (Styrene Butadiene Styrene): This is a rubber-based modified asphalt. It has a lower melting point than APP and offers superior flexibility in freezing weather. SBS can be applied using torches, cold adhesives, or hot asphalt.
The Inside Story on Fabric Reinforcements
The internal fabric reinforcement inside a mod bit roll determines its ultimate puncture resistance. In standard commercial installations, fiberglass reinforcement is used across the flat field of the roof. Polyester reinforced rolls are typically reserved for high-stress areas like angle changes, walls, and flashings because polyester handles stretching and building movement much better.
However, there is a smart upgrade to consider here. Upgrading the entire roof to polyester reinforced rolls only adds about 10 percent to the material cost. For a relatively small investment, using polyester everywhere creates a vastly superior, highly durable roof capable of handling heavy foot traffic and severe weather.
Why the Market Is Shifting to Single-Ply Membranes
While modified bitumen was a major leap forward from old built-up roofs, modern commercial single-ply membranes have taken over the market. In regions like North Carolina, the demand for SBS asphalt roofing has dropped significantly. Modern single-ply membranes now outsell SBS by an estimated seven-to-one margin.
The driving factor behind this shift is value. An SBS asphalt roofing system is going to be about twice as expensive as a high-quality single-ply TPO (Thermoplastic Polyolefin) roof.
For the vast majority of commercial projects, single-ply options offer a superior path forward:
- TPO and PVC: These white, highly reflective sheets offer cooler buildings in the summertime, and feature heat-welded seams for maximum water resistance.
- EPDM: This synthetic rubber membrane is highly cost-effective, incredibly durable, and performs exceptionally well in climates with dramatic temperature swings. We think this is the better, longer-lasting option.
Unless a building has a highly specialized structural footprint that demands heavy, multi-layer asphalt, steering your project toward modern TPO, EPDM, or PVC membranes will generally deliver the best balance of longevity, weather resistance, and upfront value.
Ready to Upgrade Your Commercial Roof?
Whether you want to discuss single-ply options like TPO and EPDM or need a custom quote for an upcoming project, the team at WNC Roofing is here to help. Contact us today to speak with a commercial roofing specialist at either of our locations or visit us online at wncroofing.com.
