In addition, Section R312.2 covers requirements for spacing between the intermediate rails. Both vertical and horizontal intermediates must be spaced so that a 4-inch diameter sphere cannot pass through the railings. Along the open side of stairways, Michigan code allows no more than a 4-3/8-inch sphere to pass through the open rails. Code officials should ensure that all railing systems are installed according to the manufacturers' installation instructions.

One supplier of guardrails and cable infill, CableRail™ by Feeney Wire Rope and Rigging, requires that vertical posts be positioned no more than 36 inches apart and that cables be spaced no more than 3 inches on center. Doing so allows the product to exceed the 4-inch sphere spacing requirements and accounts for the possibility of cable deflection.

Minimum live loads are covered in Table 301.5. Guardrails must be able to support a 200 psf single concentrated load applied in any direction at any point along the top of the rail. The infill portion of the guardrail must be able to withstand a horizontally applied normal load of 50 pounds psf.

Building Code

Requirements for guards in Michigan's Building Code are found in Section 1012. Height requirements are covered in section 1012.2. In general, there is a 42-inch height requirement for commercial applications, but residential structures built to the Commercial Code may allow 34-inch high guardrails along open sides of stairways within individual dwelling units.

Section 1012 details the opening requirements for guardrails. Opening limitations, which allow no more than a 4-inch sphere to pass through horizontal or vertical intermediate rails, are covered in section 1012.3.

Guardrails in correctional buildings, factories, hazardous and storage groups not open to the public allow 21-inch spacing. There are unique spacing requirements for assembly uses to allow for increased sightlines as identified in section 1024.14.

Strength requirements are the same as the Residential code - 200 psf concentrated live load on the top rail and 50 psf on infill. Loading requirements are found in Section 1607.7 and in Table 1607.1.