Understanding the ADA 1:12 Slope Rule
The fundamental rule for ADA-compliant ramps is the maximum running slope requirement of 1:12. This means that for every 1 inch of vertical rise, there must be at least 12 inches (1 foot) of horizontal run.
While 1:12 is the maximum allowable slope (an 8.33% grade), the ADA specifically advises that ramps should be designed with the least possible slope. Shallower slopes, such as 1:16 or 1:20, are easier for wheelchair users to navigate and are highly recommended where space permits.
How to Calculate Ramp Length
Calculating the required horizontal run of a ramp is straightforward math based on the slope ratio. You multiply the total vertical rise by the ratio value.
For example, if you need to build a ramp to navigate a step that is 18 inches high, and you are using the maximum 1:12 slope: Run = 18 inches x 12 = 216 inches. Divide by 12 to get feet, and you need a horizontal ramp run of 18 feet.
Maximum Rise and Landing Requirements
To prevent fatigue and provide a safe place to stop, the ADA mandates that a single continuous ramp run cannot have a vertical rise greater than 30 inches.
If a design requires ascending more than 30 inches, the ramp must be broken up into multiple runs with a level landing in between. A level landing is also required at the top and bottom of every ramp. Landings must be at least as wide as the ramp run leading to them and have a minimum clear length of 60 inches (5 feet).
- Maximum rise of a single run is 30 inches.
- Landings required at top, bottom, and between runs.
- Minimum landing length is 60 inches.
- If a ramp changes direction, the landing must be at least 60 x 60 inches.
When Are Handrails Required?
Not all ramps require handrails. Handrails are legally triggered under the ADA if a ramp run has a vertical rise greater than 6 inches or a horizontal length greater than 72 inches.
If either of these thresholds is crossed, handrails must be installed on both sides of the ramp segment. They must be positioned at a height between 34 and 38 inches above the ramp surface and extend at least 12 inches beyond the top and bottom of the ramp runs.
Frequently asked questions
Can I build an ADA ramp steeper than 1:12?
Generally, no. The only exceptions are for existing buildings where space limitations prohibit a 1:12 slope, in which case slightly steeper slopes (like 1:10 for a max rise of 6 inches) may be permitted under very strict conditions.
What is the minimum width of an ADA wheelchair ramp?
The minimum clear width of an ADA ramp must be 36 inches between the handrails. Some local building codes may require wider ramps (e.g., 48 inches).
Are the rules different for residential homes?
The ADA applies to commercial and public facilities. Private residential homes are not governed by the ADA, though following ADA guidelines is a best practice for home accessibility.
Does a slope of 1:20 count as a ramp?
No, surfaces with a running slope of 1:20 (5%) or less are considered walkways, not ramps, and are not subject to the specific ramp requirements for handrails or landings.