ADA Tolerances Provisions

Q2.) What are the types of “field conditions” that were anticipated where the advisory says “tolerances recognized by this provision include those for field conditions”?

A2.)  The design itself must always call for conditions that meet the specific standards. Tolerances are not an “oops factor” for careless or sloppy design.  They are instead intended to allow for the practically unavoidable imperfections that will undoubtedly occur in the field as a result of the materials and methods used in construction.  For example, a skilled brick mason cannot lay a perfectly vertical and straight wall.  A skilled tile layer cannot create a perfectly flat wall behind a toilet room grab bar.  And a concrete finisher clearly cannot guarantee that the slope of a concrete curb ramp will be consistently 8.33% across its entire surface.  Tolerances are essentially the degree of perfection expected by skilled laborers working carefully with the materials specified.  Many industry associations publish materials that specify what can be expected from their members.  Those are usually the dimensions that can safely be considered industry tolerances.  Where none exist, the effort to define them on a particular project becomes much more difficult. 

David Kent Ballast, FAIA, in his book Handbook of Construction Tolerances: 2nd Edition, offers many well-researched and thoughtfully-analyzed opinions about what numbers he believes should be considered acceptable for a wide variety of construction materials and methods. In lawsuits that the Department of Justice has filed, DOJ has taken the position that tolerances cannot be predefined but must always be considered on a case-by-case basis considering the design, the materials and methods, and the specific field conditions.  The California State Attorney General’s office has taken the same position.  The conditions that result from that approach will vary from case to case.