Construction Tolerances and the ADA
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During construction of a building or facility, allowances are made for variances (discrepancies) in the installation, including elements that must comply with the Americans with Disabilities Act (ADA). These allowances are referred to as construction tolerances. Construction tolerances are a means of controlling items such as vertical element plumb, size and/or length of structural members, and general layout and location of elements. Regardless of the material being used for a building’s elements, tolerances are often established by product and finish manufacturers in order to ensure product performance.
2010 ADA Standard 104.1.1, [Dimensions] Construction and Manufacturing Tolerances, states, “All dimensions are subject to conventional industry tolerances except where the requirement is stated as a range with specific minimum and maximum end points.”
2010 ADA Standard Advisory 104.1.1, Construction and Manufacturing Tolerances, states, “Conventional industry tolerances recognized by this provision include those for field conditions and those that may be a necessary consequence of a particular manufacturing process.”
Furthermore, “Recognized tolerances are not intended to apply to design work. It is good practice when specifying dimensions to avoid specifying a tolerance where dimensions are absolute. For example, if this document requires ‘1½ inches,’ avoid specifying ‘1½ inches plus or minus X inches.’ Where the requirement states a specified range, such as in Section 609.4 where grab bars must be installed between 33 inches and 36 inches above the floor, the range provides an adequate tolerance and therefore no tolerance outside of the range at either end point is permitted. Where a requirement is a minimum or a maximum dimension that does not have two specific minimum and maximum end points, tolerances may apply.”
A recommended good design practice would be to specify a dimension less than the required maximum (or more than the required minimum) by the amount of the expected field or manufacturing tolerance and not to state any tolerance in conjunction with the specified dimension.
Avoid thinking about construction tolerances as a list of numbers because such a list can become a shadow regulation or code. Construction tolerances have to take into account what material is used, what methods were used to build the installation, and how the element falls within the range of minimum and maximums or a specified range or dimension for each specific installation.
SUMMARY: Construction tolerances are used to allow for slight discrepancies during construction. Construction tolerances as applied to the ADA are intended:
to apply only to certain sections of the 2010 ADA Standards where dimensions are stated as single dimensions or as simple minimums or maximums
to apply primarily to difficulties caused by field conditions and the inherent limitations of materials and methods used in construction and manufacturing building materials and systems
not to be used to excuse ignorant, careless, or sloppy design or construction.