Wind uplift design for roofing can seem daunting to the uninitiated. But with a little help from online tools, it can be much more straightforward. Wind uplift is calculated for all buildings using formulas, tables, and wind maps developed by the American Society of Civil Engineers (ASCE) in their publication ASCE 7-2016. With a project’s location, building use/occupancy, building height, and roof plan, there are a number of online tools you can use to determine the wind uplift required for your building. The calculator used by the National Roofing Contractors Association (NRCA) can be found at http://www.roofwinddesigner.com/
Once the uplift pressures for your building are determined, you must choose a design for your building that meets these pressures. Roofing manufacturers list their system designs through the DORA Directory of Roof Assemblies https://www.dora-directory.com/
or through Factory Mutual Global’s RoofNav® https://www.roofnav.com/Account/Login
The DORA Directory lists roofing assemblies based on uplift testing that various manufacturers have received through third-party verification, while FM’s RoofNav lists roofing assemblies that have been tested through FM Global’s own testing facility.
Roofing assemblies that meet the minimum uplift requirements per ASCE 7-16 will meet the International Building Code (IBC); however, FM Global ratings may require additional enhancements based on their own calculations. The more stringent guidelines are due to the fact that FM Global is an insurance company and they approve designs before they issue coverage for a particular building.
While FM 1-90 is a rating used by FM Global-insured buildings as a standard for their insurance coverage, the calculation of wind load for a particular building using ASCE 7 calculations is the basis for designing a roof meeting the IBC for all buildings, whether or not they are insured by FM Global.
Meeting the standard for FM 1-90 will result in higher pressures in the perimeter and corners than using the ASCE 7 method, thereby increasing the cost of the construction of the roof. Changing these requirements at a later date or finding out your project does not require FM ratings may cause confusion during the bidding process and could result in higher bids.
Always verify your need for FM Global before proceeding with wind load design. Contact Craig Tyler at [email protected]