Technical Bulletin: Ground and Floor Surfaces

What surface characteristics are required of an accessible route?

The Americans with Disabilities Act Accessibility Guidelines (ADAAG) requires only that newly-constructed or altered ground and floor surfaces of accessible routes on sites and in buildings and facilities be stable, firm, and slip-resistant . No standards or methods of measurement are specified in scoping or technical provisions, although the Appendix to ADAAG contains advisory recommendations for slip resistance values derived from Board-sponsored research. Because the sample size was small, the testing method unique, and the findings not yet corroborated by other research, the suggested values have not been included in the body of ADAAG and should not be construed, as part of the regulatory requirements for entities covered by titles II and III of the ADA.

However, other regulations. such as those imposed by OSHA in the interests of worker safety, or design and testing standards applied by state, local, or industry mandate, such as certain ASTM (American Society for Testing and Materials) procedures, may require specific values or ranges of slip resistance.

A stable surface is one that remains unchanged by contaminants or applied-force, so that when the contaminant or force is removed, the surface returns to its original condition. A firm surface resists deformation by either indentations or particles moving on its surface. A slip-resistant surface provides sufficient frictional counterforce to the forces exerted in walking to permit safe ambulation.

Because of the great number of variables that affect the performance of a given walking surface--its slope and cross-slope, its material, texture and finish, the presence of moisture or contaminants, the material that contacts it and the method of ambulation--no single set of technical specifications or measurement standards can encompass all criteria that contribute to the safety of a walking surface.

Only slip resistance has a commonly applied unit of measurement--the coefficient of friction, which may be measured as static (at rest) or dynamic (in motion). Its calculation is complex and the methods and equipment of its measurement vary. Affected industries--floor finishes, ceramic tile, plumbing fixtures--each employ a different testing methodology in designating the slip resistance of their products. The static coefficients of friction measured according to the four major ASTM-standard testing procedures have never been correlated by research, although a considerable body of data exists.