There are essentially five different types of low-slope roofing systems, all of which Veterans Management & Restoration Services has installed in various applications throughout the United States:
Built-up roof (BUR) membranes. Commonly referred to as “tar and gravel” roofs. Generally composed of alternating layers of bitumen and reinforcing fabrics that create a finished membrane. The number of plies in a cross section is the number of plies on a roof: ex. “four plies” denotes a four ply roof membrane construction. Surfacing options for BUR systems include aggregate, glass-fiber or mineral surfaced cap sheets, hot asphalt mopped over the entire surface, aluminum coatings or elastomeric coatings. Structural metal panel roof systems for low-slope applications. Can be installed over a variety of deck types. Underlayments may or may not be utilized. Careful consideration should be given to vapor drive and the proper design and installation of vapor retarders, insulation and ventilation.
Polymer-modified bitumen sheet membranes. SBS polymer-modified bitumen membranes commonly are installed in hot moppings of asphalt (similar to BUR systems above) or cold adhesive. Some SBS modified membranes are self-adhering or torch applied.
APP polymer-modified bitumen membranes typically are heat-welded or torch-applied. An SBS modifier adds a rubberized quality to the membrane while the APP modifier adds a plasticized quality to the membrane.
Single-ply membranes. Thermoplastic membranes (PVC, TPO, CPE). Thermoset membranes (EPDM) Commonly called “rubber roofs”. Can be installed fully adhered, mechanically attached or ballasted. Seams are sealed using liquid adhesives or application specific tapes.
Spray polyurethane foam-based (SPF) roof systems. Initially composed of sprayed, closed cell insulation at various widths and profiles. Surfacing is applied over the foam and can be composed of an elastomeric coating or even a membrane.
Low slope roofing systems typically have three different components that are layered or “shingled:
Roof deck - The structural substrate, typically wood-based material.
Underlayment - Provides temporary protection until a roof covering is installed and a secondary weatherproofing barrier.
Roof covering - The uppermost component that is watershedding.
Weatherproofing layer or layers is the most important element because it keeps water from entering the roof system and ultimately the building. Reinforcement adds strength, impact protection and stability to a system. Surfacing protects the weatherproofing and reinforcement from UV degradation and weather. The final surfacing should take into account the need for increased fire resistance, high traffic, hail resistance, and reflectivity.
There are six primary types of steep-slope roofing systems, all of which have and can be professionally installed by Veterans Management & Restoration Services throughout the United States:
Asphalt Shingles. Composed of a base material (organic felt or glass-fiber mat); asphalt and fillers; and surfacing material, typically mineral granules, that provides impact and UV degradation protection as well as improved fire resistance. Should be applied over a continuous wood deck with an underlayment installed.
Clay tile and concrete tile. Manufactured by baking molded clay into tiles. Tiles can be glazed or have surface texture treatments applied. Offers a wide array of profiles, styles, finishes and colors. Should be applied over a continuous wood deck with an underlayment installed.
Metal roof systems for steep-slope applications Architectural metal panel roof systems are watershedding, not water-tight, and are intended to be utilized on steep slope roofs. Structural metal panel roof systems can be utilized on both low-slope and steep-slope roofs. Standing seam is often a generic description for a class of metal roof seams. It is derived from the fact that the seams are joined together above the panel flats. Seam types can be trapezoidal, batten, flat, bermuda and shingled.
Slate. Roofing slate is a dense, durable, naturally occurring material that is essentially nonabsorbent. Typically defined as standard smooth, standard rough, and graduated/textural slate. Should be applied over a continuous wood deck with an underlayment installed.
Wood shakes and wood shingles. Wood shingles are manufactured from western red cedar, cypress, pine and redwood trees. Available pressure treated with fire retardants and chemical preservatives for increased fire resistance and to prevent premature rot and decay in some climates. Should be applied over a continuous wood deck with an underlayment and interlayments installed.
Synthetic. Refers to synthetic materials which attempt to replicate asphalt shingles, concrete tile, clay tile, metal panels, slate, wood shakes and wood shingles. Typically contain recycled plastic and/or rubber as a key component. Relatively new and therefore long-term performance of both weatherproofing and aesthetics is unknown.