ADA Ramp Requirements, Explained

The numbers below come from the 2010 ADA Standards for Accessible Design, Section 405. They are the federal, new-construction values. State and local codes (for example California’s CBC Chapter 11B) and the technical standard most building codes adopt (ICC A117.1) can differ — and alterations to existing buildings have their own, steeper allowances. Always verify against the authority having jurisdiction (AHJ) and the code edition actually adopted where you are building.

The core ramp rules (new construction)

• Running slope: 1:12 maximum (8.33%) — §405.2. A surface gentler than 1:20 is a “sloped walking surface,” not a ramp, and doesn’t trigger ramp handrails.
• Cross slope: 1:48 maximum (~2.08%) — §405.3.
• Clear width: 36” minimum between handrails — §405.5.
• Maximum rise: 30” per run — §405.6. Past that, you must insert a landing.
• Landings: 60” long minimum, and 60” × 60” where the ramp changes direction — §405.7. Provide one at the top and bottom of every run.
• Handrails: required on both sides of any run that rises more than 6” — §405.8.

The catch for existing buildings

When space is constrained in an alteration, the older 1991 ADAAG allowances (still invoked in those cases) permit steeper ramps: 1:10 to 1:12 for a max rise of 6”, and 1:8 to 1:10 for a max rise of 3”. This is the classic “gotcha” — new construction is 1:12, but a renovation may legally be steeper.

How the calculator uses these

Give it a total rise and it returns the horizontal run, the sloped ramp length, the number of intermediate landings, and whether handrails are required — flagging anything steeper than 1:12. Use it to size a ramp quickly, then confirm the details against your adopted code.