Roofing is defined as material that is used for building or repairing a roof. The roof itself is composed of several primary parts. When grouped, these parts are known as either a roof assembly or a roof system. Now, a roof assembly is a mixture of interrelated roof components. It includes the roof deck, air or vapor retarder, insulation, underlayment, and primary roof covering designed to weatherproof a structure. All things considered, a roof system is also a mixture of interrelated roof components but generally consists of the primary roof covering, underlayment, and roof insulation designed to weatherproof and, at times, improve the building’s thermal resistance. Let’s take a look at a few of the different categories of roof systems available for residential, commercial, and institutional structures.

Steep-Slope Roof Systems

Steep-slope roof systems are regularly installed on slopes greater than 3 inches per foot (3:12). This category includes water-shedding types of roof coverings such as asphalt shingle roof systems, clay and concrete tile roof systems, metal shingle roof systems, slate roof systems, and wood shake and wood shingle roof systems. All of these systems are designed for use as single-layer overlapping or multilayered, water-shedding roof components that rely on the slope of a roof substrate to effectively shed water. Lastly, asphalt shingles are designed for use as multilayered while tiles are designed for use as overlapping, and metal shingles are designed for use as single-layer overlapping or multilayered. In the end, they are all roof components that rely on the slope of a roof substrate to completely shed water.

Low-Slope Roof Systems

Low-slope roof systems are commonly installed on slopes 3 inches per foot (3:12) and less. This category consists of weather-proof types of roof coverings, such as membrane roof systems. The four types of common roof membranes are built-up (BUR) membranes, polymer-modified bitumen membranes, single-ply membranes, and liquid-applied membranes. Built-up and polymer-modified bitumen membranes build the roof covering and are made up of several layers of membrane material. While single-ply membranes use one layer of membrane material. Two leading types of single-ply membranes are thermoset sheets, such as ethylene propylene diene monomer (EPDM) and thermoplastic sheets such as polyvinyl chloride (PVC) as well as thermoplastic polyolefin (TPO). Liquid-applied membranes are built in place from a liquid resin and reinforced with polyester reinforcing fabric or fleece. These four roof coverings are applied on low-slope or flat roof substrates and require positive drainage. Positive roof drainage is provided by sloping the structural framing or deck. That option may not be feasible or even possible on an existing building. Though, a designed tapered system or an insulating fill can be sloped. A combination of slope and roof drains, scuppers and gutters installed in proper locations will add positive drainage.

Metal and SPF Roof Systems

Metal panel and spray polyurethane foam (SPF) roof systems are also considered low-slope roof systems. Metals used in roofing can be divided into several categories, such as naturally weathering metals and metallic-coated metals. Then, there are 15 or more types of metals which are selected based on performance, suitability, compatibility, economics, degree of desired corrosion resistance, and aesthetics. Next are system types. The two primary types of metal panel roof systems are architectural and structural. Sub-categories include hybrid metal panel roof systems and exposed fastener metal panel roof systems. Both the architectural and exposed fastener metal panel roof systems are water-shedding and rely on the slope of a roof substrate to effectively shed water. The SPF roof system is created by a process of combining two liquid components, A & B, and when mixed, it expands 20 to 30 times its original liquid volume to form a closed-cell foam. In order to achieve positive drainage or to meet a specified thermal resistance, it is applied in varying thicknesses.

To put it briefly, there are several systems, but the slope of the substrate designates which roof system is applicable for installation on new or existing structures. Contact us today for more information about steep or low-slope roof systems.