There are many different options for a commercial roof today. If you are in the design process for a commercial roof, keep reading for some information regarding several different types of commercial roof systems. There are five general classifications of low-slope commercial roof systems and six classifications of steep-slope commercial roof systems. We are only experts on low-slope roofs, so we cannot speak to steep-slope systems.
Low-Slope Commercial Roof Systems
Most low-slope commercial roof systems are made up of three basic components: Weatherproofing layer(s) which keep water from entering the roof assembly. Reinforcement which, as you may have guessed, adds strength and stability to the roof. Surfacing is the top layer that protects the other two layers from sunlight and weather. Now let’s look at the five major classifications:
Built-Up Roof (BUR)
Commonly referred to as “tar and gravel” roofs, BUR roofs are often composed of alternating layers of bitumen and reinforcing fabrics. BUR roofs can be installed directly to roof decks or insulation. The surfacing on BUR is commonly aggregate (gravel, slag), glass-fiber, mopped-on hot asphalt, or aluminum coatings. BUR commercial roof systems are hailed for their insulation properties; they are often made up of four or more roofing layers so they have excellent R-values and keep the building at the temperature the occupants want.
Structural Metal Panel
Metal roofs are one of the most common commercial roof systems. Metal roofs provide an excellent water barrier because of their hydrostatic characteristics. Metal roofs can be installed over many different types of substrates. The substrate can provide continuous support to the roof or spaced support. Metal roofs utilize underlayment, or felt paper, above the roof deck and beneath the metal panel system.
Modified Bitumen (MB)
MB systems have been used in the US for around 40 years. They are composed of reinforcing fabrics and rolled on material. MB commercial roof systems are typically installed in a 2-ply fashion. MB systems are often installed through hot moppings of asphalt (like BUR) or cold adhesive with an adhesive coating on the back of the roll. They can also be heat-welded or torch-applied, but this method is much more dangerous. MB commonly utilize aggregate, mineral, metal foil-laminate or smooth applied liquid surfacings. Cold adhesive installations have become the preferred method for MB as heat applied methods have been found to be very dangerous, leading to several building fires.
These are typically factor-manufactured sheet membranes. These membranes are typically 30-60 mils thick. These systems can be installed fully-adhered, mechanically attached or held down via ballast. They are often installed using muliple adhesion methods. For instance, the insulation could be mechanically attached to the substrate while the roof membrane is fully adhered to the insulation. They generally do not receive surfacings.
Spray Polyurethane Foam (SPF)
These commercial roof systems are constructed by mixing and spraying a two-component liquid that forms the base of the system. A surfacing is applied on top of the foam to protect it from the elements. These surfacing are commonly silicone, acrylic, butyl rubber, Hypalon, and a few less common materials. Mineral granules or sand are often cast into the surfacing to provide increased durability, traction, and aesthetic value. For more information on our roofing SPF roofing system, click here.
If you would like more information on any of these roofing systems, check out this great resource provided by the NRCA: Commercial Roof Systems Guide. If you have any questions, don’t hesitate to contact us. We’d love to chat.