DSA IR 11B-8 - USE OF PREDETERMINED CONSTRUCTION TOLERANCE GUIDELINES FOR ACCESSIBILITY (with revisions issued through Jan. 2011)

4. ABSOLUTE DIMENSIONS: In the few cases where absolute dimensions are indicated, the application of construction tolerances is most likely to be influenced. In construction, the technological capacity to achieve an exact and precise placement of an architectural element in some cases can be quite difficult. In addition, the technological capacity to place one particular architectural element at a specific distance may not be the same for a different architectural element. For instance, consider the requirement that water closets (toilets) be an absolute 18" from the adjacent wall to the centerline. Variations in wall finish thicknesses or structural members could easily influence the final constructed condition, especially in concrete slab construction.

In such water closet installations, it would not be unusual to see minor ½" deviations (17½" to 18½") based on these field conditions. Therefore, it is reasonable to assume that at least some minor deviation from absolute dimensions could be expected for water closets.

In recent projects however, water closet centerline dimensions in newly constructed toilet rooms for adults measured as much as 21" and as little as 15" from the adjacent wall. In both cases the amount of variation equaled or even exceeded the entire thickness of the combined wall finishes. Under analysis, it was clear that the lack of care and coordination exercised in the planned placement of the wall, the rough plumbing, and the wall finish was the cause of the deviation, rather than any field condition or manufacturing variant.

While acceptance of a ½" water closet centerline variance may be allowed as a DSA jurisdictional building code approval, it should be noted that such acceptance may not necessarily have effect or provide immunity under a judicial review.