November- How to Handle Construction Tolerances

One of the biggest questions we get is about construction tolerances and how that is affected by the ADA guidelines, especially if a range is given in the CBC. In our opinion, the best design practice is to state the range in your drawings instead of giving an exact dimension.

For a full understanding of this opinion, we look at the defining regulations of the ADA which include: the text of the Americans With Disabilities Act, the Federal ADA Standards, the California Building Code, and case law. Case law is the area that is most unknown to us as architects and not lawyers. It is from the case law that we learn more about how construction tolerances are viewed in construction related disability access lawsuits. In Kirola Vs. City and County of San Francisco, the courts faulted Kirola's experts for not considering construction tolerances and cited the standards of ADAAG for applying construction tolerances.



The ADAAG states:

SCOPING 104.1.1 Construction and Manufacturing Tolerances. All dimensions are subject to conventional industry tolerances except where the requirement is stated as a range with specific minimum and maximum end points.

So we know that when an absolute dimension is called out in the code, construction tolerances are applicable. However, what happens when we are given a range for design.

When a range is given, legally the element must be designed and built within the range. No construction tolerances are considered acceptable. So as design professionals what is our best practice to ensure our clients are protected?

We recommend stating the dimensional range on your drawings and specifications instead of listing an exact dimension.



Let's look at some examples.


First let's look at 11B-609.4 and 11B-609.3

In this first example, we will consider the position of the grab bar. The CBC states:

Grab bars should be 33 inches min to 36 inches max

If you were to go to find the average of the range and indicate that as an exact measurement on your drawings, you would indicate that the grab bar should be installed at 34.5". If the toilet installed has a high tank the top would measure above 33 inches. If this was the case, there would be less than 1.5" between the tank and the grab bar. This would create a non-compliant issue due to code 11B-609.3 which requires 1 1/2 inches minimum between the grab bar and any objects below.

11B-609.3 ...the space between the grab bar and projecting objects below and at the ends shall by a minimum 1 1/2".

If we design with ranges, we allow for the contractor in the field to make the necessary adjustments to avoid these barriers of access created by overlapping requirements. If ranges were given, they could have installed the grab bar at 36 and it would have been compliant in the range.


Another example comes from 11B-604.2 Location of the Toilet.


Water closet shall be 17 inches minimum to 18 inches maximum from side wall.

If on your drawings you find the average and dimension your toilet at 17.5 but during construction a change is made to the tile selection and the new tile is 1/4" thicker. The toilet would now be installed 17.25" from the wall. This would mean that based on the CBC the toilet is compliant, it could create confusion and result in change orders to move the toilet to match the drawings.


Our final example will bring us to 11B-405.2.


The max running slope of a ramp is 8.33% and the maximum cross slope is 2.083%.

11B-405.2 gives us the maximum running slope of a ramp: 8.33%. No minimum slope is defined, but a range is still implied. In this instance, the minimum slope for a ramp is 5.01% (any less steep and it would be a sidewalk). Construction tolerances would not apply because the ramp is not required to be an exact 8.33%. It is our recommendation when designing a ramp to not design it to the maximum slope; use caution and design to a greater degree of accessibility to allow for tolerances in the field during construction. The same is true for cross slope. 11B-405.3 defines the maximum cross slope as 2.083% but an implied minimum cross slope of 0%.



If you have questions about accessibility or are interested in working with an accessibility consultant on your next project, please feel free to contact us.



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