What Am I Standing On?

Most curb ramp inspections go wrong before the first measurement is taken.

First, know which rulebook you're in — because in California you're in two at once. The 2010 ADA Standards are federal and apply nationwide. California Building Code Chapter 11B applies here on top of them, and on curb ramps it's consistently the stricter of the two. Where they differ, you meet the more restrictive requirement. And in several places the ADA is simply silent — it says nothing at all about blended transitions, parallel curb ramps, or grade breaks. A curb ramp can be perfectly compliant under the federal standard and still be a violation in California. That gap is where the demand letters come from, and it's usually the work of a designer who only had one of the two books open.

The next mistake isn't sloppy work with the level. It's that the inspector never established what element they were looking at. A curb ramp, a blended transition, and a ramp all get you from one elevation to another, and on the ground they can look nearly identical. But they're three different elements under Chapter 11B, with three different sets of requirements. Measure one against another's limits and you'll reach a confident, well-documented, wrong conclusion.

Here's the part that surprises people: the running slope isn't just a requirement to check. It's the thing that tells you which element you have.

A blended transition is defined by a slope of 1:20 or less — a raised pedestrian crossing, depressed corner, or similar connection between a circulation path at sidewalk level and a vehicular way. A curb ramp is steeper than 1:20, up to a maximum of 1:12. And the code defines a ramp as any walking surface with a running slope steeper than 1:20, which on its face would sweep in curb ramps too.

So slope alone doesn't finish the job. The other half of the test is what the element does. A curb ramp exists because a curb exists — it's the way through the curb, from walk to street or parking. A ramp is a walking route in its own right, up to an entrance or between levels, and it comes with its own rulebook: handrails, edge protection, intermediate landings. Different element, different course of action.

I use three questions, in this order, before anything else gets written down.

Is there a curb face involved? If the surface connects a walk to something above or below an adjacent curb face, you're in 11B-406 territory. If not, it's a ramp under 11B-405.

What does the level read? 1:20 or flatter, connecting sidewalk to vehicular way, is a blended transition. Steeper than 1:20 is a curb ramp, and it has to meet 1:12.

Are both surfaces at substantially the same elevation? Then it's a curb cut, and a curb cut is not a curb ramp.

The level decides this, not the drawing. An architect can write "blended transition" on a plan sheet all day. If it measures steeper than 1:20 in the field, it isn't one — it's a curb ramp, and every curb ramp rule just landed on it: the 1:12 slope, the 48-inch width, the 48-inch landing.

Worth knowing what the code doesn't say. There is no minimum or maximum length for a curb ramp run or a blended transition. Slope and width are regulated; length isn't. A short steep run and a long gentle one are judged by the same numbers, and the only thing length does is determine what slope you can achieve over the rise you have. So don't go looking for a length requirement to write someone up on — put the level on it and let the slope answer the question.

Curb ramp type matters too, and there are three arrangements you'll meet. A perpendicular curb ramp runs square to the curb — you walk down it in the same direction it drops. A parallel curb ramp runs in line with the direction of travel, the walk itself ramping down to a lowered landing, and it's the one you'll often find serving access aisles in a parking lot. A diagonal sits at the corner, pointed at the intersection, and puts you at a spot where you can head off in more than one direction. Each carries requirements the others don't.

Two more places the federal standard falls short of California, both worth committing to memory. Width: the ADA says 36 inches, 11B says 48. Top landing: the ADA says 36 inches, 11B says 48. A curb ramp built to federal minimums is a full foot narrow on both counts here.

Naming the element is the first line of every inspection. Everything after it depends on getting that right.

I put together a course on inspecting curb ramps yourself — fourteen videos, a field manual, and the checklist I use in the field. Details here.