Skip to main content

The roof of a building has one main job, to protect the inside of a building from harsh weather elements. There are many different types of roofing systems and each serves a specific purpose. A commercial building’s roof is typically a flatter or low sloped roof because HVAC, and plumbing systems might be installed on top of the roof. These low slope roofs will have a roof access hatch or door that allow maintenance technicians and workers pass through and gain access to the roof and repair any damaged or broken equipment.
Some of the more common roofing systems include: Metal, Built‐up, Modified Bitumen and Single Ply Membrane Roofs. Each has its own unique characteristics and application. Below is information on each of these roofing systems that will hopefully help you identify them a little easier.

Metal Roofing – Low slope structural metal roofing is commonly known as standing seam roofing and consists of interlocking panels that run vertically along the roof surface. These panels generally come with a painted mill finish or a clear acrylic finish. Durable metal roofing is a becoming a popular roof system because of is 40 to 60 year life span. Some of the common metal roofing materials include:
Corrugated galvanized steel, copper, aluminum, coated stainless steel, zinc and tin. Metal roofing can have an attractive, finished look, strong fire resistance ratings and are stronger and more sustainable then other roofing options.

Built‐up Roofing – Built‐up roofs have been popular for more than 100 years. The system is composed of alternating layers of bitumen (asphalt) and fabrics called roofing felts. The felts are reinforced with either glass‐fiber mats or organic mats and when joined with the bitumen form a durable roofing membrane. The number of “piles” on a roof implies the number of layers. Built‐up roofing is one of the oldest and most flexible roofing system and is more cost effective and easier to repair. It is also UV‐resistant and may be coated to reflect heat. The main concern is Built‐up roofing has a lifespan that is one of the shortest and it can be difficult to locate a leak as the roof ages.

Modified Bitumen Roofing – 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 (asphalt) is a sticky, black, and viscous liquid or semi‐solid form of petroleum. Mod bit membranes are typically installed as a two or three ply 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. 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.

Single Ply Membrane Roofing – 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. 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 because of their proven ability to withstand the potentially damaging effects of sunlight and most common chemicals generally found on roofs. Thermoplastic membranes are fabricated from polymers which soften when heated and harden when cooled. These 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 thermoplastics polyolefins (TPO) are the most common types of thermoplastic roofing membranes.
Determining the best choice for a single ply system depends on several factors, including cost. Important consideration are building height, wind exposure, anticipated foot traffic and aesthetics.

Roofing systems are a vital part of any structure. Make sure and follow the manufacture installation recommendation when installing a new roof or repairing an existing roof. Until next time my friends, be prepared and stay safe.
Reference: “Choosing a Flat Roof” by