CFC Reviews CMHC Design Report: Construction Tolerances – Fasteners

Other fastener types require anywhere from 1.5 to 3.0 times depth of embedment, which depends in turn on load, concrete strength, and fastener size.
No matter what fastener is selected, it is unlikely that less than 50 mm minimum will do. This means that the normal position for edge of slab must be 50 mm (or more, for minimum edge distance depending on fastener type), plus around 10 mm (for fastener placement), plus 25 mm (for slab position error), minus 46 mm (half the stud depth). That is a total of 35 to 40 mm from the outside face of framing. The error in position of the framing does not enter into this calculation, if the framing is positioned relative to the shelf angle after the angle is installed and adjusted.
Where the slab should be located depends in part on how the stud track fasteners are placed. Are their locations eyeballed, measured relative to slab edge, or measured from face of framing? If the fasteners are individually placed by measurement from the slab edge, and if they do not have to be centred on the track, the framing can be placed closer to the nominal slab edge position than if they are required to be centred.
Clearly, the insulation at edge of slab will be less than 75 mm thick, most of the time. Eliminating the insulation at slab edge, and securing the shelf angle to the slab with shims and grout has been advocated as a way of keeping this location dry and frost-free. The energy-efficient alternative is to use a smaller shelf angle, supported on brackets, with the space behind it filled with insulation that can adapt to available space, either foam-in-place, or, if firestopping is also needed, ceramic fibre batt. Reviewed by Guiseppe Strazzeri.