Dimensional Tolerances in Construction and for Surface Accessibility

1.1.5 Flatness of walk running slope. For pedestrian paths up to and including 6 ft (1.8 m) wide, measure for flatness of the running slope at 10 ft (3 m) increments along the midpoint of the width of the walk by using a 10 ft (3 m) unleveled straightedge resting on high spots. Measure the distance between the straightedge and the surface at the largest gap. See Fig. 1(a). Alternately, electronic devices may be used that provide an equivalent 10 ft (3 m) flatness measurement.

For pedestrian paths over 6 ft (1.8 m) wide, measure for flatness of the running slope at 10 ft (3 m) increments along two paths, each 2 ft (600 mm) from the edge of the path. Using a 10 ft (3 m) straightedge resting on high points, measure at 10 ft (3 m) increments along the two lines. Measure the distance between the straightedge and the surface at the largest gap. See Fig. 1(b).

This method of measurement is consistent with the tolerance requirements of ACI 117 and can check for localized flatness. However, this section defines where the measurements should be taken.