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Written by Rabia Shinaishin, R.A.
Not many would argue that construction is an exact science. As much as architects try to cover the bases on our drawings with minimum/maximum dimension ranges, field conditions don’t always work in our favor. There are times when the tolerance in a built condition is acceptable, but when it comes to accessibility tolerances it’s a different story.
An interesting tolerance issue came up during an accessibility study we have been working on for a local university. We were tasked with identifying instances of ADA (Americans with Disability Act) noncompliance on campus and providing recommendations for addressing any issues found. A ramp slope was evaluated as part of a larger accessible route and although the overall length and rise met the 1:12 ADA requirement, it was noted as being slightly steeper than the maximum 1:12 at isolated areas within the overall length. When the issue was brought to light, an intense debate ensued between the University and those on our team who made the discovery. Most cases of noncompliance are attributed to the age of facilities, but the ramp in question was built less than 10 years ago as an accessible ramp. How could this happen??
Well, construction is not an exact science, that’s how it happens. Though the original ramp designer may have indicated that the ramp could have no more than a 1:12 slope, the built slope may still be off. The reality is that there are any number of field conditions that could affect the slope of a concrete ramp and could result in a slope being noncompliant with ADA.
So, what’s the solution here? Does the University have to redo the ramp? The answer is a solid: it depends. The ADA does indeed account for construction tolerances in certain cases. The 2010 ADA Accessibility Guidelines (ADAAG) states that:
All dimensions are subject to conventional industry tolerances except where the requirement is stated as a range with specific minimum and maximum end points (§104.1.1).
Essentially, the tolerance must fall within the minimum/maximum range when required by ADA, but “conventional industry tolerances” may be acceptable for other conditions. In the case of the University’s existing, but relatively new ramp, the ramp exceeded the 1:12 ratio by a few tenths of a percent (less than ¼”). There is no minimum slope given in the ADAAG, only a maximum slope. That being the case, a conventional industry tolerance could be found to be acceptable here.
Now what is considered a conventional industry tolerance? The answer is really a matter of opinion, based on what is reasonable and how much the ramp deviates from the required 1:12. It can be argued that this small percentage of deviation from the 1:12 ratio would be considered a conventional industry tolerance for a concrete ramp. For this project, our take on it is that general acceptable tolerances can be established by the University to address this ramp and other projects going forward.
For architects, how do we do our part and help contractors stay within ADA compliance, given that our designs cannot always be built to a T? One thing to consider is to maybe indicate tolerance ranges that are well within the acceptable range per ADA. Where instead of designing for a 1:12 ramp, we design for a 1:14 ramp. It may not always be possible or desired, but in the long run perhaps it will save us all some heartache by remembering that construction is not an exact science.