Dimensional Tolerances in Construction and for Surface Accessibility

Purpose of the project

Accessibility standards reference industry guidance in the measure of field and construction tolerances. However, few trade and materials specifications include tolerances for features that are relevant to usability by people who have disabilities. For instance, when this project began, tolerances for the measurement of the slope, flatness, and smoothness of exterior walking and rolling surfaces in concrete, asphalt, unit masonry, and other materials had not yet been developed by industry groups.

The current project was undertaken to encourage and support construction industry stakeholders to fill in the gaps in existing tolerances and procedures and to set specific tolerances and procedures for measurement for particular materials and assemblies. The purpose was not to suggest or revise the dimensional limits set in the ADA/ABA Accessibility Guidelines nor to set specific tolerances within the body of the Guidelines, but rather to assist industry in developing dimensioning and measurement conventions appropriate to the different materials and methods used in exterior and interior walking/rolling surfaces so that practitioners and regulatory agencies could refer to them for guidance.

The Access Board contracted with David Ballast, FAIA, CSI with Architectural Research Consulting to manage the project and provide assistance and advice to industry associations as required to meet the goals of the project.