Specifying Metal Thickness for Architectural Panels

Use of gauge to designate sheet metal thickness is discouraged by numerous international standards organizations. For Example, ASTM (formerly known as American Society for Testing and Materials) states in specification ASTM A480-10a. “The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning.” A specifier fails to make a traceable connection to the design standard by providing only a gauge identifier(i.e., 24 ga.). This could lead to an inappropriate or under/ over-design of the cladding system.Thickness is a critical parameter in the performance of steel sheet and coil. According to the Metal Construction Association (MCA) and a formula provided by US Steel, a 10% difference in thickness could result in as much as a 150% difference in impact resistance. A significant factor in the performance of metal in hail or impact conditions.

Specification of Material Thickness
The Metal Construction Association (MCA) recommends the following approach when specifying thickness of metal cladding systems:

  • Gauge designations should not be used in building specifications to define thickness. Specified dimensions of the base material should be used, without allowance for coating thickness.
  • If gauge designations are used in architectural drawings for brevity, the accompanying notes or specifications should specify the thickness for all gauges referenced.
  • Thicknesses should be specified using nominal dimensions to two significant digits with tolerances applied 50% over/50% under.