Flat Roofing Systems

Although simple and utilitarian, the main goal of a roof system is to maintain the watertight integrity of a building and keep its contents dry. Today’s variety of flat or low slope commercial roofing options (roof pitches ranging from ¼:12 to 3:12) is no longer simple and has grown considerably in the last 50 years.

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Lets take a quick look at the different Flat Roof Systems that are available.

Asphalt Roofing Systems

We support and offer a full line of asphalt based commercial roofing systems. A long-dependable choice for low slope roofing, asphalt falls into three basic categories:

  • Built Up Roofing
  • Modified Bitumen
  • Hybrid Systems (a combination of Mod Bit and BUR)

Built Up Roofing (BUR) Systems

Popular in North America for more than 100 years, Built Up Roofing (BUR) Systems are composed of alternating layers of bitumen (asphalt) and fabrics called roofing felts. The felts are reinforced with either glass-fiber mats or organic mats (ply sheets) and when joined with the bitumen form a durable roofing membrane.  The number of “plies” on a roof implies the number of layers, i.e. “four plies” denotes a four-layer flat roof membrane system.

BUR systems are redundant, meaning if one layer breaks down, multiple remaining layers provide immediate protection. These systems also offer great tolerance for building stress and resistance to thermal shock, high puncture resistance and outstanding membrane strength and toughness for proven long-term durability.

BUR systems can include SBS, fiberglass or organic felts and offer many options to suit a variety of building needs. The key to this system is the repetitive layers. BUR also is known for superior fire resistance from external flames. Reflective surfacing options also are available to offer maximum membrane protection, superior puncture resistance and high resistance to foot traffic and mechanical maintenance.

With standard application procedures, IKO BUR Systems offer robust protection for today’s buildings and are available in traditional four-ply. Product options include the following:

Base Sheets – Saturated or coated felts placed as the first ply in some low-slope roof systems.

Felts – Reinforcing fabrics also are called roofing felts or ply sheets. Roofing felts are reinforced with either glass-fiber mats or organic mats.

Bulk Asphalt – A proven waterproofing material and is suitable for use in selected damp proofing and waterproofing applications.

Modified Bitumen (Mod Bit) Systems

Mod Bit systems include factory-fabricated layers of asphalt that are “modified,” using a rubber or plastic ingredient for increased flexibility and combined with a reinforcement for added strength and stability. Bitumen (or asphalt) is a sticky, black, and viscous liquid or semi-solid form of petroleum. It’s found in natural deposits or may be a refined product and is used for both road surfacing and roofing. Bitumen displays a thermoplastic quality when softened by heat.

In modified bitumen, there are two primary modifiers used today: APP (atactic polypropylene) and SBS (styrene butadiene styrene). APP and SBS refer to the type of polymers that are added to the asphalt. A variety of reinforcements are used with the asphalt, including fiber glass and polyester mats and scrims. Scrim is a reinforcing fabric made from continuous filament yarn in an open mesh construction.

Mod Bit membranes are typically installed as a two- or three-ply (multiply) system. The type of modifier used may determine the method of sheet installation: mopped down using hot asphalt or heat welded to melt the asphalt so that it flows onto the substrate. Seams are sealed by the same technique. The membrane system may be held in place on the roof by fully adhering the base sheet, mechanically attaching the base sheet or using ballast.

Mod Bit Systems Options:

  • Heat Welded Roofing Systems
  • Fully Adhered
  • Mechanically Attached
  • Fire Rated
  • Reflective and Eco Friendly
  • Heavy Duty Composite
  • Cold Applied
  • Self-Adhered
  • APP Mod Bit
  • Mod Bit/BUR Hybrid Systems

Single Ply Membrane Systems

The single ply roofing systems market has grown exponentially in the past 40 years. Considered a reliable commercial roofing application, single plies offer an extended service life and require relatively low maintenance. In many cases, commercial single ply roofing systems are backed by a manufacturer’s warranty.

The Single Ply Roofing Industry (SPRI) classifies single ply commercial roofing membranes as flexible sheets of compounded synthetic materials that are manufactured in a factory to strict quality control requirements. Single ply roofing systems provide strength, flexibility and long-lasting durability. The inherent advantages of these pre-fabricated sheets are the consistency in quality of the products that are manufactured, the versatility in their attachment methods and their broader applicability.

There are two major categories of single ply membranes: thermosets and thermoplastics.

  • Thermoset membranes are compounded from rubber polymers. The most commonly used polymer is EPDM or Ethylene Propylene Diene Monomer. EPDM is a durable rubber roofing solution and available in both black and white. Thermoset membranes are successful for use as roofing materials because of their proven ability to withstand the potentially damaging effects of sunlight and most common chemicals generally found on roofs. The EPDM Roofing Association (ERA) offers detailed information on EPDM roof resources.
  • Thermoplastic membranes are fabricated from polymers which soften when heated and harden when cooled. These factory-made sheets are applied on the job site using one of the standard installation techniques for sheet membrane systems (fully adhered, mechanically attached or ballasted). This process is repetitive provided the material is not heated above the point at which decomposition occurs. The membranes can be welded together with heat or solvents, and when welded, develop a bond strength which equals or surpasses the strength of the base material. Polyvinyl chloride (PVC), blends or alloys of PVC and thermoplastic polyolefins (TPO) are the most common types of thermoplastic roofing membranes.

Liquid Applied and Spray Foam Roofing Systems

As outlined in the Manual, liquid applied membrane roofing includes hot and cold polymer-modified asphalt, single-component asphalt or coal tar-extended urethane and two-component urethane elastomer. Liquid applied membrane systems require rigorous preparation of the substrate, which must be dry and dust-free with patched cracks.


Determining the best choice flat roofing system depends on several factors, including cost. Let our team help you make the right choice for your project. Give us a call or complete our online for to speak with one of our flat roof experts.