Dimensional Tolerances in Construction and for Surface Accessibility

1.1.13 Flatness of ramp running slope. Measure flatness in the running slope of ramps at 12 - in. (300 mm) increments by using successive, overlapping 24 - in. (600 mm) lengths using a 24 - in. digital inclinometer. For each measurement lay the instrument such that it reads the steepest slope or spans between two high points. See Fig. 4. Alternately, measurement can be made by using a digital inclinometer mounted on a 12 - in. (300 mm) beam or similar instrument with accuracy as stated in 1.1.1. Measuring 12 - in. (300 mm) lengths can account for local variations in slope that may be difficult for a person in a wheelchair or using other mobility aids to use.

Measuring one - foot (300 mm) lengths allows for a reasonable check on local variation that can be accomplished easily and inexpensively with a 2 - ft digital inclinometer or other available instruments.

For ramps from 36 in. (915 mm) up to, and including, 5 ft (1525 mm) wide between handrails measure along two lines parallel to the length of the ramp. Each line should be approximately 6 in. (150 mm) from the inside (ramp side) edge of the handrail. For ramps where handrails are not used, such as curb ramps, measure 6 in. (150 mm) from the edge of the ramp. See Fig. 5(a).

For ramps over 5 ft (1525 mm) in width between handrails measure along an additional line for each additional 36 in. (915 mm) of width or fraction thereof beyond 5 ft (1525 mm). The additional line or lines should be spaced equidistant between the two outside measurement lines. See Fig. 5(b).

Measurement at 6 inches from the handrail or edge of curb ramps is approximately where the inside wheel of a wheelchair would be if the handrail is being used.

Requiring measurement along the running slope for every additional 36 inches means that measurements will always be taken to account for a distance between 24 inches and 42 inches. This is approximately where the path of a wheelchair or other mobility aids would be used without requiring excessive lines of measurement for wide ramps.