Truncated Domes – Detectable Warnings

The terms “Truncated Domes” and “Detectable Warnings” are often used synonymously, but it is important to draw a distinction. Although the 1991 Americans with Disabilities Act Accessibility Guidelines (ADAAG) requires a truncated dome type of detectable warning surface, this has not always been the case and has created conflicting opinions of what is needed to comply.

In 1994 the ADA requirement for detectable warnings on curb ramps was placed on suspension to conduct further research on the detectability of various types of detectable warning surfaces. During the suspension period, detectable warnings consisting of grooves, striations, exposed aggregated, expanded metal stamps, and dyed concrete were evaluated. The conclusion reached was that other forms of detectable warnings were too similar to pavement textures, cracks and joints and were proven less effective than a surface of truncated domes.

The suspension expired on July 26, 2001 consequently putting back into requirement truncated dome detectable warnings on curb ramps. Therefore, on all new construction or alteration projects, under the Americans with Disabilities Act, truncated domes are the only acceptable form of detectable warnings.

The importance of knowing the difference, however, between the terms “Truncated Domes” and “Detectable Warnings” lies with the fact that many State Building Codes refer to assorted versions of the International Building Code or ANSI Standard. For instance, Florida’s Building Code is based on ANSI A117.1-1986 which requires detectable warnings comprised of “exposed aggregate concrete, cushioned surfaces made of rubber or plastic, raised strips or grooves”; not truncated domes.

An excerpt from the Florida Building Code:

11-4.29 Detectable warnings.
11-4.29.1 General.
Detectable warnings required by Sections 11-4.1 and 11-4.7 shall comply with 11-4.29 . 11-4.29.2 Detectable warnings on walking surfaces.

(1) All detectable warning surfaces required by the code shall be governed by the requirements of ANSI A117.1-1986.

(2) Detectable warning textures on walking surfaces shall consist of exposed aggregate concrete, cushioned surfaces made of rubber or plastic, raised strips, or grooves. Textures shall contrast with that of the surrounding surface. Raised strips or grooves shall comply with Figure 11-40 (a) and Figure 11-40 (b). Grooves may be used indoors only.

Although the latest version of ANSI has been updated to incorporate truncated domes, there tends to be a lag between the release of a new standard and its implementation by independent agencies. Nevertheless, ANSI is only one standard setting agency and while building codes use it for reference, it is also crucial to abide by the requirements set forth in the Americans with Disabilities Act which is federally enforceable antidiscrimination legislation.

When constructing or altering commercial facilities or places of public accommodation, be sure to note that regardless of the regulations established by the local enforcement agency, Title III of the ADA explicitly requires truncated dome detectable warnings without exemption.

 

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