Roof system ratings
Roofing systems are rated based on testing completed by the manufacturer’s testing agency and verified by the evaluation service. Each building has a specific wind uplift design requirement based on calculated wind uplift pressures, taking into account parameters such as geographical location, building height and geometry, enclosure classification, and topographic factors (Figure 1). These design pressures are typically calculated either by following the requirements of American Society of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structures, or if Factory Mutual (FM) certification is required for insurance purposes or other reasons, the provisions for determining wind uplift forces outlined by FM 1-28, Wind Design.
IBC requires the calculation of wind pressures for components and cladding elements, including the roof membrane. The intent of the components and cladding calculation is to ensure veneers, windows, roofing systems, soffits, and other nonstructural components are adequately fastened to the structure and they continue to function during a design wind event (To see an example of a roofing failure, click here.). The designer calculates the required uplift pressure in pounds per square foot and matches it with the tested uplift capacity of that specific roofing system and configuration of supporting substrate and insulation. Important variables to consider include, but are not limited to:
- roof deck material (e.g. concrete, steel, plywood, oriented strand board [OSB], or gypsum roof board);
- base sheet (e.g. adhered or mechanically fastened);
- single-ply systems (e.g. ethylene propylene diene monomer [EPDM], polyvinyl chloride [PVC], or thermoplastic polyolefin [TPO]);
- built-up or single-ply system membranes;
- ballast density;
- fastener types and spacing;
- insulation and coverboard;
- adhesive materials and ribbon spacing; and
- primers or other required components.
To gain approval and compliance with the code, the manufacturer engages a testing lab to perform the testing required by IBC. Once this is completed and maximum capacities are also developed, the manufacturer sends the data, along with other pertinent information, to ICC-ES or another accredited code compliance authority and submits an application for a compliance report. ICC-ES then reviews the data provided and validates compliance with the code. Upon a successful review and validation process, an evaluation report (ESR) is written and issued for the products and assemblies as previously described.
For low-slope roofing, the published report typically contains a series of tables presenting the materials and attachment methods for each tested system to allow the designer to select one with greater capacity than calculated demand. A generic example of what these tables typically look like is presented in Figure 2. The ESR is only applicable to the codes specifically referenced in the document since the code and testing requirements may change over time.