New Accessibility Standards, Part 2: Dimensions

Architects are often surprised when they learn that construction tolerances are permitted by the Texas Accessibility Standards, especially if they have just been informed by an over zealous inspector that a toilet will need to be moved one eighth of an inch.

Just look in section 3.2 of the Texas Accessibility Standards (TAS).

3.2 Dimensional Tolerances.

All dimensions are subject to conventional industry tolerances for field conditions.

In the new 2010 ADA Standards for Accessible Design (SAD), the permissible tolerances are more specific.

104.1 Dimensions.  Dimensions that are not stated as “maximum” or “minimum” are absolute.

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.

The biggest difference is the clarification that tolerances only apply when a fixed dimension is specified or when a maximum OR minimum is given.  If a dimension is expressed as a range with a maximum AND a minimum, the field condition must be within that range.

Here are some examples of how construction tolerance could be applied (results may vary between agencies and inspectors):

Element TAS Requirement TAS Construction Tolerance 2010 SAD

Requirement

2010 SAD

Construction Tolerance

Water Closet 18” o.c. fixed 17” -19” o.c. 16”-18” o.c. No tolerance allowed
Ramps 8.33% max

(1:12)

May vary by 1% but average over a run should not exceed 8.33% 8.33% max

(1:12)

May vary by 1% but average over a run should not exceed 8.33%
Top of Dining or Work Surfaces 28”–34” ½” tolerance 28” minimum and 34” maximum No tolerance allowed
Door Width 32” minimum clear None. Manufactured door assemblies do not require a construction tolerance. 32” minimum clear None. Manufactured door assemblies do not require a construction tolerance.

To hear the latest from TDLR, subscribe to the TDLR List Server http://www.license.state.tx.us/newsletters/TDLRnotificationLists.asp

And check back here to learn more about the upcoming changes.

-Jeromy

 

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5 Responses to New Accessibility Standards, Part 2: Dimensions

  1. Bill Franz says:

    The requirement for RAMP RUNNING SLOPE is stated as a range with specific minimum (1:20) and maximum (1:12) end points. There is plenty of room within this range for construction tolerances. With these stated minimum and maximum end points construction tolerances must be within this range. No construction tolerance outside this stated range is permitted.

    106.5.53 Ramp is defined: A walking surface that has a running slope steeper than 1:20 (the minimum).
    405.2 Slope. Ramp runs shall have a running slope not steeper than 1:12 (the maximum).

    2010 SAD ADA and 2012 TAS

    • jeromymurphy says:

      I disagree. You are just inferring that the minimum slope is 1:20. If a range was intended, it would have been stated as a range in 405.2. Advisory 405.2 even recommends that the “least possible running slope” should be used on a ramp.
      Are you suggesting that it would be a violation of the Standards to build a ramp with a 1:25 slope?

  2. Bill Franz says:

    Again – a RAMP is defined in ADA SAD and TAS SAD 106.5.53 as having a running slope steeper than 1:20. Anything less is not a ramp and would not be subject to the requirements of a ramp. Least possible slope is definitely desirable. A walkway surface at less than 1:20 is even more desirable than a ramp.

    106.5.53 Ramp is defined: A walking surface that has a running slope steeper than 1:20 (the minimum).
    405.2 Slope. Ramp runs shall have a running slope not steeper than 1:12 (the maximum).
    403.3 Slope. The running slope of walking surfaces shall not be steeper than 1:20. (walkways – not ramps)

    2010 SAD ADA and 2012 TAS

    The full requirement for 405.1 Slope including the [definition] for a ramp would be:

    405.2 Slope. Ramp runs shall have a running slope [steeper than 1:20 and] not steeper than 1:12.

    With these stated minimum and maximum end points construction tolerances must be within this range. No construction tolerance outside this stated range is permitted.

    See also PROWAG 2011 –
    Proposed Accessibility Guildelines for Pedestrian Facilities in the Public Right of Way
    R304.4.1 Running Slope. The running slope of blended transitions shall be 5 percent maximum.
    R304.2.2 Running Slope. The running slope of the curb ramp shall be 5 percent minimum and 8.3 percent maximum

  3. Ken Otten says:

    Although I understand Bill’s point, Jeromy is correct. The fact that a ramp is *defined* as a walking surface having a running slope steeper than 5% does not constitute a minimum dimension. If that were the case, the language would have clearly defined ramps as having a slope between 5% and 8.33% (1:20 and 1:12).

    If the advisory for using the least possible slope (which was, in fact, a requirement in the 1994 TAS) were adopted by construction contractors in the field, we would rarely need to employ a tolerance for ramp slopes in the first place.

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