Dimensional Tolerances in Construction and for Surface Accessibility

1.2.6 When local variations (flatness) in running slope of ramps are measured according to 1.1.13 at least 80% (rounded to the nearest whole number) of the measurements should not exceed an 8.3% slope. The remaining measurements should not exceed a 10% slope.

Allowing a small percentage of localized slopes to exceed 8.3% is based on the allowable slopes in ADA/ABA - AG (2004) for existing buildings of 1:8 (12.5%) for maximum rises of 3 inches and 1:10 (10%) for maximum rises of 6 inches. The 1980 ANSI A117 standard also allowed this with the additional provision that an existing ramp slope of up to 1:8 could have a maximum run of 2 feet (0.6 m). Allowing 20% of local variations to slope up to 10% seems reasonable for a distance of one foot. This would mean that localized dips and high points in a 2 - foot distance would be about ¼ in. (6 mm) or a little less.