The Americans With Disabilities Act (ADA)


The ADA was signed into law July 26, 1990 by President George H.W. Bush.
It was modeled after the Civil Rights act of 1964 as an “equal opportunity” law for people with disabilities.


The ADA “ensures access to the built environment for people with disabilities”.

ADA Standards...

“establish design requirements for the construction and alteration of facilities subject to the law”.


“apply to places of public accommodation, commercial facilities, and state and local government facilities”.

Facilities that follow ADA Standards uphold the accessibility requirements outlined by state or local laws. Though these state or local laws are based on national models, there can be significant variations.

When federal and state laws prove to be inconsistent, building owners and design professionals are responsible for ensuring compliance with both.


State or local officials are responsible for the enforcement of state codes, and usually do so through plan reviews and building inspections.

The ADA relies on litigation in federal courts for enforcement.  Local officials do not enforce the ADA on behalf of the federal government.


ADA Accessibility Guidelines (ADAAG)

The design standards for detectable warnings, as stated by the ADA are as follows:

4.29.1 General. Detectable warnings required by 4.1 and 4.7 shall comply with 4.29.

4.29.2* Detectable Warnings on Walking Surfaces. Detectable warnings shall consist of raised truncated domes with a diameter of nominal 0.9 in (23 mm), a height of nominal 0.2 in (5 mm) and a center-to-center spacing of nominal 2.35 in (60 mm) and shall contrast visually with adjoining surfaces, either light-on-dark, or dark-on-light.

The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact.

4.29.3 Detectable Warnings on Doors to Hazardous Areas. (Reserved).

4.29.4 Detectable Warnings at Stairs. (Reserved).

4.29.5 Detectable Warnings at Hazardous Vehicular Areas. If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings, or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning which is 36 in (915 mm) wide, complying with 4.29.2.

4.29.6 Detectable Warnings at Reflecting Pools. The edges of reflecting pools shall be protected by railings, walls, curbs, or detectable warnings complying with 4.29.2.

The ADA Standards: Chapter 7

705 Detectable Warnings

705.1 General.  Detectable warnings shall consist of a surface of truncated domes and shall comply with 705.

705.1.1 Dome Size.  Truncated domes in a detectable warning surface shall have a base diameter of 0.9 inch (23 mm) minimum and 1.4 inches (36 mm) maximum, a top diameter of 50 percent of the base diameter minimum to 65 percent of the base diameter maximum, and a height of 0.2 inch (5.1 mm).

705.1.2 Dome Spacing.  Truncated domes in a detectable warning surface shall have a center-to-center spacing of 1.6 inches (41 mm) minimum and 2.4 inches (61 mm) maximum, and a base-to-base spacing of 0.65 inch (17 mm) minimum, measured between the most adjacent domes on a square grid.

705.1.3 Contrast.  Detectable warning surfaces shall contrast visually with adjacent walking surfaces either light-on-dark, or dark-on-light.

705.2 Platform Edges.  Detectable warning surfaces at platform boarding edges shall be 24 inches (610 mm) wide and shall extend the full length of the public use areas of the platform.

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