Anthropometry of Wheeled Mobility Project: Final Report

4.3.2 Seat Height

Seat height is an important dimension for establishing the height of built-in seating, toilet heights, tub heights, shower seat heights and other transfer related surfaces. Keeping the height of a transfer surface close to the height of a wheelchair seat reduces the effort necessary to transfer and provides a safer environment, especially in bathing and toilet rooms. However, seat height for wheelchair users can be significantly different than comfortable seat height for ambulant people. Seat heights for transfer surfaces in the ADA-ABA are 430 mm - 485 mm (17 in. - 19 in.) for water closets, shower seats and tub seats and 405 mm - 485 mm (16 in. −19 in.) for pool transfer lifts.

Our research results indicate that a range of seat heights is appropriate to accommodate the wide variety of different needs. Ranges for built elements should accommodate ambulatory individuals as well because they are the vast majority of the population. Designing only for WhMD users would cause discomfort and safety problems for too many people. Our findings show that the values of the current U.S. accessibility standards are below the mean values of each of the three WhMD user groups. The mean occupied seat heights were 495 mm (19.5 in.) for manual chair users, 538 mm (21.2 inches) for power chair users and 549 mm (21.6 in.) for scooter users. For the manual chair users, the 5th −95th percentile range was 430 mm - 566 mm (17 in. - 22.3 in.). Therefore, the current accessibility standards are more accommodating to those WhMD users with low occupied seat heights. If the goal is to accommodate the mean seat height for each of the WhMD user groups, a range of 495 mm – 549 mm (19.5 in. - 21.6 in.) is likely to be more accommodating. An application of these results could be in the design of fixed toilet heights. If the goal is to accommodate the 5th percentile occupied manual chair user seat height and the 95th percentile scooter user seat height, a range of 430 mm - 635 mm (17 in. - 25 in.) is needed. Conventional seating heights are within a ranch of 381 mm - 406 mm (15 in. −16 in.) for adults. Thus, designing even for the range of WhMD users would cause a problem for everyone else. This finding suggests that the solution to the problem should be sought in technology rather than building standards, just like it has with ergonomic office chairs. The findings could be applied to establish the range of height adjustable seat and support surfaces. Meanwhile, we recommend that the current top of the acceptable range be increased to 508 mm (20 in.) and that consideration be given to providing an assistive technology solution, a seat riser, in temporary lodging settings.