surfaces: firmness and stability testing
surfaces: firmness and stability testing

accessible surfaces

it's the LAW

According to the Americans with Disabilities Act (ADA) Standards for Accessible Design 302.1, accessible routes must have ground and floor surfaces that are firm, stable, and slip-resistant. In addition, 1017.2 of the Architectural Barriers Act (ABA) Accessibility Standards state that the surface of trails, passing spaces, and resting intervals shall be firm and stable.

Unfortunately, not all ground is naturally inclusive. Surfaces that are not firm, stable, and slip-resistant endanger individuals and limit accessibility for wheelchair, cane, crutch, and walker users, parents with strollers, and other individuals with limitations in mobility.

firm, stable, and slip-resistant

It’s clear that surfaces must be firm, stable, and slip-resistant. But these terms are subjective. How to quantitatively assess the firmness, stability, and slip-resistance of a given surface is not so clear.

In order to help determine whether or not a surface actually complies with accessibility requirements, the terms have been defined by the US Access Board. Chapter 3 of the Access Board’s Guide to the ADA Standards states that, “accessible surfaces remain unchanged by external forces, objects, or materials.”1


so what do those terms actually mean?


A firm surface resists deformation by applied forces.1 Firmness is defined as the degree of surface resistance to deformation, especially by indentation or the movement of objects.2


A stable surface resists movement.1 Stability is defined as the degree to which surface resists change from contaminants or applied force, so that when the contaminant or force is removed, the surface returns to its original condition.2


The degree to which a surface provides frictional counterforce to the force exerted in walking to permit safe ambulation.2

1  United States Access Board, “Chapter 3: Floor and Ground Surfaces” in “Guide to the ADA Standards” (guide, United States Access Board, 2010), accessed 25 July 2019,
2  Peter Axelson and Denise Chesney, “Accessible Exterior Surfaces Technical Article” (technical article, U.S. Architectural and Transportation Barriers Compliance Board, 1999), accessed 25 July 2019,, Introduction.

how to measure

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