ASCE 7 vs FM
Wind uplift design for roofing can seem daunting to the uninitiated, but with a little help from online tools, it can be 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 location, building use/occupancy, building height, and roof plan, you can use any of a number of online tools to determine the wind uplift required for your particular building. The National Roofing Contractors Association Calculator can be found here.
Once the uplift pressures for your building are determined, choose a design that meets these pressures. Roofing manufacturers list their system designs through the DORA Directory of Roof Assemblies here or through Factory Mutual Global’s RoofNav here.
The DORA directory lists roofing assemblies based on uplift testing that various manufacturers have received through third-party verification. RoofNav lists roofing assemblies that have been tested directly through FM Global’s own testing facility.
Roofing assemblies which meet the minimum uplift requirements per ASCE-7-2016 will meet the building code. However, FM Global ratings may require additional enhancements based on their own calculations. The more stringent guidelines for FM Global are because they are an insurance company and 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 or result in higher bids.
Always verify your need for FM Global before proceeding with wind load design. Contact Craig Tyler at [email protected] with questions.
Once the uplift pressures for your building are determined, choose a design that meets these pressures. Roofing manufacturers list their system designs through the DORA Directory of Roof Assemblies here or through Factory Mutual Global’s RoofNav here.
The DORA directory lists roofing assemblies based on uplift testing that various manufacturers have received through third-party verification. RoofNav lists roofing assemblies that have been tested directly through FM Global’s own testing facility.
Roofing assemblies which meet the minimum uplift requirements per ASCE-7-2016 will meet the building code. However, FM Global ratings may require additional enhancements based on their own calculations. The more stringent guidelines for FM Global are because they are an insurance company and 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 or result in higher bids.
Always verify your need for FM Global before proceeding with wind load design. Contact Craig Tyler at [email protected] with questions.
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