Understanding the ins and outs of modified bitumen roofing

By Polyglass. 

Considering a new roof? Here is why modified bitumen roofing is the choice for millions of contractors.  

Modified bitumen roofing has become one of the most common commercial roofing systems in the industry throughout the years. What started as an experiment in the industry, is now considered a superior option to other roofing types. But what makes this material unique? In this guide, we’ll breakdown what modified bitumen is made of and what the different types are, in addition to its many benefits like its durability, flexibility and ease of installation.  

What is modified bitumen roofing? 

Modified bitumen is thought of as the evolutionary cousin of the built-up roofing systems (BUR) that have been used on low-slope roofs for more than 100 years. It is made of asphalt combined with polymerized rubber or plastic, then reinforced with fiberglass to create a rugged-yet-flexible waterproof membrane. 

Modified bitumen roofing is primarily used on flat or low-slope commercial roofs. Depending on the type and material, these membranes may be installed as part of a two-layer system or as part of a multi-ply system. 

History of modified bitumen 

Modified bitumen first appeared in commercial roofing in the mid-1960s in Europe. Before that time, the conventional roofing system used on most commercial structures was built-up roofing (BUR), a complicated system of alternating layers of asphalt and fabric with a top layer of gravel. 

While BUR was a tried-and-true method, it was heavy, costly to install, difficult to repair, and often had trouble holding up against extreme temperatures. By integrating the bitumen with polymers and fiberglass into a simple membrane, the developers of modified bitumen hoped to simplify the roofing process while resolving some of the most common issues with BUR. 

Overall, the efforts were successful. Modified bitumen proved to be easier to install while providing enhanced protection compared to BUR systems, even in very cold temperatures. By 1975, modified bitumen was in wide use here in the United States, and today, it has all but replaced BUR as one of the most reliable roofing materials on the market. 

Application methods for modified bitumen 

Modified bitumen typically comes in membrane form, in rolls that are installed directly onto the substrate via an adhesive. The material may be heat welded, cold-adhered, or in some cases, self-adhered (as with many of Polyglass’ top products that feature ADESO® self-adhering technology). 

Some modified bitumen membranes may also be mechanically attached. Most applications call for at least two layers (a base layer and a cap layer), but in some cases, it may be installed in a multi-ply system of three or more layers. 

Modified bitumen membrane types 

Modified bitumen typically falls into one of two varieties: APP and SBS. 

APP membranes 

Commonly nicknamed “plastic asphalt,” atactic polypropylene (APP) membranes consist of asphalt blended with plasticized polymers that become elastic under high temperatures. APP is resistant to UV rays and is a good choice for structures seeking a “cool roof” effect. 

SBS membranes 

SBS stands for styrene-butadiene-styrene, but it helps to think of SBS roofing as “elastic” or “rubberized” asphalt. This membrane combines asphalt with polymerized rubber for natural flexibility and elasticity. SBS is a good choice for buildings whose roofs expand and contract with extreme temperature changes, as well as roofs subject to higher winds.   

What are the benefits of modified bitumen roofing? 

1. Tear-resistance. Modified bitumen offers outstanding durability and tensile strength, making it resistant to tears from weathering, debris and even consistent foot traffic. 
2. Waterproof. When properly installed, modified bitumen provides some of the best waterproofing protection of any roofing material on the market. Redundant layers enhance this quality even further. 
3. Ease of installation, repair and maintenance. Modified bitumen is easy to maintain, and if it does tear or leak, it can be easily patched. 
4. Flexibility. Modified bitumen expands and contracts with changing weather conditions without losing integrity. 
5. Energy-efficient. Certain types of modified bitumen offer high UV resistance and reflect the sun’s rays for lower energy bills. 

Modified bitumen FAQs 

How long does modified bitumen last? 

Modified bitumen has an average life expectancy of about 20 years, possibly more with proper care and maintenance. 

How is modified bitumen roofing applied? 

Modified bitumen is typically applied by heat (torch) welding, cold-process adhesive or self-adhering membranes. 

How is modified bitumen roofing repaired? 

Modified bitumen roofing is typically easily repaired by cutting away the damaged piece of membrane, applying a modified bitumen patch, and applying a sealant to protect it. 

What does APP stand for? 

APP stands for atactic polypropylene, a thermoplastic material used in modified bitumen. 

What does SBS stand for? 

SBS stands for styrene-butadiene-styrene, a form of synthetic rubber used in modified bitumen. 

What are the downsides of modified bitumen roofing? 

Modified bitumen requires a bit of skill to install, and it presents a potential fire hazard when heat-welded. Self-adhering modified bitumen membranes solve this problem — not only do they save contractors time and labor, but they also do not require a torch for installation. 

What are the benefits of self-adhered membranes? 

As previously mentioned, self-adhered modified bitumen is much easier to install since the adhesive layer is already applied. It also eliminates the fire risks associated with torch welding. 

What is cold-applied roofing? 

Cold-applied roofing refers to roof membranes that are attached with a cold-process (water or solvent-based) adhesive rather than by heat welding. 

Can you install modified bitumen in cold weather? 

Modified bitumen can be installed in cold temperatures with certain considerations and precautions. For best results, choose roofing products that are predicted for cold-weather installation. For example, Polyglass’ low-temperature Polar cap and base membranes are specially designed for installation in freezing temperatures. 

Original article source: Polyglass