Modified Bitumen Roofing Guide

No matter what commercial property you oversee, your roof will always protect you and your clientele from the weather. When operating a warehouse in the high temperatures in Nevada or an apartment complex in New York with its freeze-thaw cycles, you must select the appropriate materials to ensure you will protect the asset and keep it for a long time.

Modified Bitumen Roofing, or as it is commonly called, mod bit, is an asphalt membrane system that is doubled and fortified with polymers to keep it flexible and strong. It is consider a standard of the industry for low-slope roofs across the USA. However, its success is often a function of determining the most appropriate materials for the region’s climate, especially in states such as FL, NV, PA, NY and CA.

In mod bit roofing systems, the more important aspect in the asphalt is the type of modifier used. There are 2 common types in the roof and it will depend greatly on the type of climate your building is in.

SBS roofing definition: is a rubberized modifier as it adds elasticity to the asphalt. Visualize a rubber band, it can keep its shape, be pulled in different directions and will always be able to return to its original form.

SBS membranes display remarkable flexibility and elasticity, even at very low temperatures. As a result, this type of membrane is ideal for installation on roofs that undergo extensive movement, settlement, or thermal shock. The material remaining pliable in subzero tem peratures means that it does not suffer from the cracking issues that more rigid systems multitarea membranes do.

Unlike the rubber-like quality of SBS systems, atactic polypropylene roofing (APP) systems also have a plastic modifier, resulting in a membrane that is tougher and more rigid.

APP’s critical elements are better plasticity and UV resistance. It also has a higher temperature threshold than SBS different membranes, which resulted in a very high capacity for heat resistance in built-up roofs. It also undergoes installation forming a very tensile, seamless covering that can undergo a lot of sun exposure.

After deciding the type of membrane, the next decision on the modified bitumen roofing membrane is how to attach it to the substrate. The dominant two options are torch down and self-adhered (peel-and-stick).

With this method of installation, a torch flame is used to melt a few inches of the membrane’s underside as the installer unrolls it. Upon cooling, this forms a permanent bond between the sheet and substrate.

• Advantages: Provides a truly durable and watertight seal, is materials wise one of the most affordable systems, and has been field tested with successful results for years.
• Disadvantages: Use of open flame. This fire risk must be carefully considered during installation. Additionally, relies on specialized contractors who have the necessary experience, training, and insurance.

Self-adhered systems have a factory-applied adhesive to the back of the sheet. The installer removes a release film and easily presses the membrane into position.

• Advantages: Offers a safer installation as there are no open flames, and is free of fumes and odors. In most cases, installation is faster and can be installed in fire sensitive areas with no risk.
• Disadvantages: Generally, the material costs are higher, and a heat welded bond is not available. It requires the substrate to be clean and dry for the adhesive to bond properly.

This is highly location dependent. In areas prone to wildfires, like California or Nevada, or in places with high population density like New York City, open flames on rooftops can be heavily regulated or banned for fire safety. In these cases, peel and stick is frequently the only available option.

When budgeting your first commercial roof, it is essential to understand the variables involved. Generally, the pricing structure for modified bitumen is within the same range of other commercial systems, although not without the same fluctuations due to some of the same considerations.

For the installed cost, you will be looking at approximately $4.00 to $8.00. This figure is quite broad.

Some of the variables influencing the cost include:

• Polymer Selection: Installation of SBS systems tends to be a little more expensive because of the requirements for hot asphalt or cold adhesive (if not torching) due to the installation specs.
• Installation Method: Modified Bitumen, torch down, tends to be more expensive from a material standpoint, although you may save on insurance and labor costs from the torch down method.
• Roof Profile: Additional penetrations, such as HVAC units and roof vents will significantly increase the labor needed.
• Location: Geographical discrepancies in labor are quite vast with examples such as the rural reaches of Pennsylvania and downtown San Francisco, or Manhattan.

It is advisable to obtain as many detailed quotes as you can from local contractors, as some of the contractors will have a better feel for the regional pricing breakdown.

When roofing systems are manufactured with a one size fits all approach, the results can be subpar. This is more evident than with modified bitumen roofing in the different climate scenarios found in the United States.

For statewide building code references, you can consult resources like the International Code Council (ICC).

In humid, coastal regions like the coast of california and florida, the roof is subject to salt spray, high humidity, and heavy rain.

• Recommendation: While APP membranes provide good UV resistance, sea integrity remains the primary concern, especially with proper torch-down application which provides the most secure seam against standing water.
• Concerns: Algae growth is prevalent with ponding water as it slows drainage and further accelerates membrane degradation.

These areas contain the most extreme UV exposure and high daytime temperatures.

• Recommendation: APP is the most favorable form of atactic polypropylene roofing. Being plasticized, it is the most heat tolerant, and will resist flowing or softening.
• Efficiency: Applying a reflective coating over the cap sheet combats heat absorption. This will prolong the life of the roof, and reduce costs associated with cooling the building.

This is the northeast of the United States, which has to deal with the adverse effects of snow loads, frigid temperatures, and cyclical freeze-thaw events.

• Recommendation: Styrene butadiene styrene roofing (SBS) is a must. When a roof is rigid, it may crack if temperatures fall to zero and the building undergoes thermal contractions. SBS is a must, as it will remain flexible and absorb these movements.
• Efficiency: Membrane strength is vital to withstanding the weight of snow. Proper insulation is to prevent ice dams.

Constraint: Many historic buildings or high-rises prohibit the use of propane torches due to fire risk.

Cold applied adhesives or self-adher adhesives (peel-and-stick) membranes are frequently the only options for retrofitting these features in the safest way possible.

To fully appreciate the merits of “mod bit”, a contrast with built-up roofing would be beneficial.

BUR is the conventional “tar and gravel” roofing, consisting of bitumen and reinforcing fabrics, alternated and capped with aggregate.

Despite the long-standing history of BUR, modified bitumen is considered the more modern and advanced roofing option. BUR provides the waterproofing strength of asphalt but is enhanced with polymers for more durability and quality control.

What is mod bit roofing if not a versatile solution for modern challenges? Whether you are dealing with the desert sun or a Nor’easter storm, this roofing system provides a durable shield for your commercial property.

To ensure the roofing system is effective for decades:

• Choose SBS for cold climates with large swings in temperature (PA, NY).
• Choose APP for hot, high-uv climates (NV, Inland CA, FL).
• Always check fire codes for torch down applications in metropolitan areas.
• Work with a licensed, reputable roofing contractor who is familiar with your state’s building codes. A mod bit system can be maintained to provide more than 20 years of effective roofing protection.

Get a precise, custom assessment for your modified bitumen system from the experts at aconengineering.com.

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