ADA Parking Slope Requirements: The 2% Rule Explained

The Rule That Quietly Drifts Out of Compliance

Most accessible-parking violations are obvious. A faded symbol, a missing sign, a too-narrow aisle. Slope is different. A space can be the right size, painted perfectly, signed correctly, and still fail because the pavement underneath it tilts a fraction of a percent too much. Slope is invisible to the eye and only shows up when someone puts a level on it. That makes it the rule that quietly drifts out of compliance over the years.

Our ADA parking compliance guide for Oregon covers the full set of requirements. This page is about the one measurement that surveying equipment catches and human eyes do not: the 2 percent slope limit.

What the 2 Percent Limit Actually Means

The 2010 ADA Standards cap the slope of accessible parking spaces and their access aisles at 2 percent in any direction. That applies to both the running slope (the direction a car travels into the space) and the cross slope (side to side).

Two percent is a small number. It works out to a quarter inch of fall per foot of length. Across a 20-foot-deep parking space, that is a maximum of about 5 inches of total drop from front to back. Go beyond it and a person transferring to a wheelchair can find their chair rolling away from them, which is exactly the hazard the limit exists to prevent.

The limit is "in any direction," which means you cannot trade a steep running slope for a flat cross slope or vice versa. Every direction across the space has to stay at or under 2 percent.

Where the Slope Limit Applies

The 2 percent rule is not limited to the parking space itself. It governs a connected set of surfaces:

• Accessible parking spaces. The full area of each accessible stall.
• Access aisles. The hatched aisle beside the space, which must also be level with the space.
• The accessible route. The path from the space to the building entrance must stay at or under 2 percent cross slope, with running slope limited to 5 percent (steeper grades become ramps with their own rules).

A space and aisle that are individually flat but sit at different heights from each other also fail, because the aisle must be level with the space it serves. The whole assembly has to sit on one plane within tolerance. The dimensional side of these spaces is covered in our ADA parking stall dimensions guide.

Why Slope Is the Hardest Rule to Keep

Counts, signs, and stripes stay fixed once installed. Slope does not. Pavement moves.

• Settling. As the base material beneath asphalt consolidates over time, the surface settles unevenly. An accessible space that was poured at 1.8 percent can drift past 2 percent as one corner drops.
• Ground movement. Oregon's clay-heavy soils swell and shrink with the wet and dry seasons, heaving and dropping the pavement above them.
• Freeze-thaw. Winter freeze-thaw cycles lift and crack surfaces, changing the local grade.
• Poor original construction. Some lots were never within tolerance to begin with, having been graded by eye rather than surveyed.

This is why a lot that passed inspection at construction can be out of compliance a decade later without anyone touching it. Slope is the one parameter that degrades on its own.

Repaving Can Help or Hurt

A repave is the moment slope gets fixed or broken, depending on how it is done.

A simple sealcoat or thin overlay follows the existing grade. If the base is tilted past 2 percent, a sealcoat just puts a fresh face on a non-compliant slope. The drainage and the tilt come right back.

A proper correction means addressing the grade itself, which can involve grinding down high areas, building up low ones, or in serious cases reworking the base before repaving. When a lot is being altered anyway, that is the efficient time to bring accessible-area slopes back into tolerance, and depending on the scope of work it may be required rather than optional. The Oregon-specific obligations around alterations are detailed in our Oregon ADA parking requirements page.

Standing Water Is the Visible Symptom

You cannot see a 2.3 percent slope. But you can often see its consequence: standing water. Ponding in an accessible space or aisle after rain is a strong signal that the grade is off, because a properly sloped surface within the 2 percent envelope still drains, while a surface that has settled into a low spot collects water.

In Oregon, where the rainy season runs much of the year, ponding in accessible areas does double damage. It is a slope-compliance red flag and it is a direct barrier, forcing a wheelchair user through standing water to reach the building. If you see water pooling in or near your accessible spaces, treat it as a slope problem until a survey proves otherwise.

How Slope Gets Verified

You do not guess at slope, you measure it. A compliance survey uses a digital level, a smart level, or survey-grade equipment to take readings across the space and aisle in multiple directions. The readings are compared against the 2 percent ceiling. This is part of a thorough ADA compliance audit process, and it is the step that separates a real audit from a visual once-over.

Because slope changes over time, a measurement from five years ago is not a current pass. If your lot has settled, cracked, or heaved since the last survey, the accessible spaces deserve a fresh reading. This is general guidance, and the only way to know your lot's actual slope is to measure it on site.