Today, we take a look at the different commercial roofing systems that are installed on top of flat and low-slope buildings across America.
Types of Flat and Low Slope Roof Systems Today
In general, there are five basic classifications of commercial roofs commonly used on flat or low-slope buildings:
- Built-up roofing
- Metal roofing
- Modified bitumen roofing
- Single-ply roofing
- Spray polyurethane foam (SPF roofing)
Low-slope roof systems may include several functional components, such as:
- Reinforcement, which can add strength, stability, and dimensional support to a roofing system.
- Weatherproofing layers, which help prevent water from entering the roof assembly.
- Surfacing, which may protect underlying roofing materials from ultraviolet exposure, weathering, traffic, or other conditions. Some surfacing materials can also provide reflective or other performance characteristics.
We cover each type of commercial roof mentioned above below.
Roof Types and Their Features
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The reinforcement layers may be referred to as roof felts or ply sheets. Depending on the system, built-up roofing may be installed over insulation or an appropriate roof deck or substrate.
The bitumen used in BUR systems may include asphalt or other compatible materials. Surfacing can include aggregate such as gravel or slag, mineral-surfaced cap sheets, coatings, or other protective materials.
Metal roofing—Metal roofing is widely used on commercial buildings. Materials may include galvanized steel, coated steel, stainless steel, copper, aluminum, and other metal roofing products.
Metal roofs can develop corrosion, loose fasteners, failed seams, coating deterioration, or other problems over time depending on the material, environment, installation, and maintenance.
Protective coatings may be applied to suitable metal roofing systems for purposes such as corrosion protection, reflectivity, or restoration. Coating materials and preparation requirements vary by roof type and product.
Pros & Cons of Various Roofing Systems
Learn MoreGenerally speaking, two common types are SBS polymer-modified bitumen membranes and APP polymer-modified bitumen membranes. Installation methods can include hot asphalt, cold adhesives, self-adhered applications, heat welding, or torch application depending on the specific product.
Surfacing may include aggregate, mineral surfaces, coatings, or metal foil, depending on the roofing system.
Single-ply roofing—Single-ply roofing membranes are factory-manufactured sheets. Generally speaking, there are two major categories: thermoplastic membranes, including PVC and TPO, and thermoset membranes, including EPDM rubber roofing.
Single-ply systems may be fully adhered, mechanically attached, or ballasted depending on the membrane and roof design. Reinforcement may include polyester fabrics, scrims, glass fiber, fleece backings, or other materials depending on the product.
SPF roofing—SPF roofing is created by applying liquid components that react and expand to form a rigid spray polyurethane foam layer over a suitable substrate.
The foam can be applied at different thicknesses to provide insulation value and, in properly designed applications, may also be used to help create slope for drainage.
Because spray polyurethane foam requires protection from ultraviolet exposure and weathering, a compatible protective coating or other surfacing system is installed over the foam.
Common protective coatings used with SPF roofing may include:
- Polyurethane coatings
- Acrylic coatings
- Silicone coatings
- Other compatible protective coatings specified for the SPF system
SPF installation requires specialized equipment, proper application conditions, and experienced installers. The protective surface also needs regular inspection and maintenance.
Concluding Thoughts
There are many commercial roofing types available today, and each has its own advantages, disadvantages, maintenance needs, and potential problems.
Over time, commercial roofing systems can experience leaks, weathering, membrane deterioration, corrosion, damaged seams or penetrations, drainage problems, or other conditions.
When an existing roof is structurally sound and otherwise suitable for restoration, a coating or other restoration system may provide a cost-effective alternative to full replacement and may help extend the useful life of the existing roof.
Before restoration, the roof should be evaluated for wet insulation, structural deterioration, serious drainage problems, damaged roofing materials, failed seams or penetrations, trapped moisture, and other conditions that may need to be corrected first.
A commercial roofing contractor can inspect the existing roof and discuss whether repair, restoration, recover, or replacement is appropriate.
