The minimum recommended slope of a handicap ramp is 1:12 because it is the threshold for the strength required of a handicapped person to move unaccompanied up or down the ramp. Construction of a handicap ramp uses the relationship between vertical height to horizontal length to determine the recommended slope.
Several factors determine the size of a handicap ramp, including space available, budget and the capacity to meet Americans With Disabilities Act ramp guidelines, specifications and code, as well as OSHA guidelines and IBC2006 standards for wheelchair ramp handicapped access. Due to the limited mobility of handicapped persons, the minimum recommended slope for a handicap ramp is 1:12. Ramps with gentler slopes, such as 1:16 or 1:20, have longer runs that require less strength of a handicapped individual to negotiate the ramp unassisted.
For example, interior handicap ramps in public or commercial settings can have a slope as steep as 1:12. However, external ramps at these same types of settings must have a slope no greater than 1:20. The gentler slope can reduce the instances of discomfort or injury caused by the inability or difficulty to negotiate the comparatively steep incline of the ramp and can aid in negotiating the ramp in inclement weather conditions.