Disabled Access Wheelchair sizes and dimensions

Why do Architects design buildings and spaces with certain sizes for the disabled?
The answer is that they blindly follow written codes without understanding them! If that shocks you please read on.

Keep in mind that as Architects we get very little continuing education for disabled access design and construction. And the only reason they do it is because the law now requires us to.

Majority of the dimensions that all architects should be familiar with are geared towards a person on a wheelchair. This is because a person on a wheelchair has mobility. And just as an able-bodied individual functions, a person with a disability needs to be able to do the same functions, however limited. With that premise, this article aims to check and explain vertical and horizontal dimensional challenges the person might face, as it applies to use of wheelchair. I hope that you can visualize the use and therefore become more aware of your built surroundings. As you read my article, please realize that I am not trying to point out the flaws of a traditional wheelchair design, my aim is however to show the limitations of this apparatus so that you can design for it.

What is important to realize is that although a wheelchair is a much-needed tool for a person with a disability, it does have limitations. Additionally depending on the disability, a person may or may not be able to use the reach ranges at a seated position to its greatest possibility.  If you can imagine an able-bodied person sitting down on a chair and attempting to reach to get what you they need, a person with a disability on a wheelchair is always at a disadvantage. Therefore it is always necessary to literally imagine yourself in the persons seat.
Prior to us looking at reach ranges the most critical find would be to understand what the real size of the wheelchair is, so that we can understand its limitations. Keep in mind that wheelchairs sizes and types vary, and dimensions required by building codes and ADA are usually larger than the actual wheelchair. Throughout this article when dimensions are mentioned I am mainly referring to the graphics you see below.

Disabled access wheelchair vertical dimensions

Graphic # 1: Vertical and horizontal dimensions

Let us first look at the heights that are critical to wheelchairs, starting from ground up:
1.    Toe: 8 inches measured to the top of the toe
2.    Seat: 19 inches measured to the top of seat cushion
3.    Lap: 27 inches measured to the top of person’s lap where an item can be used.
4.    Armrest: 30 inches measured to the bottom of where the arm is placed.
5.    Handle: 36 inches measured to the handle where an assistance pushes the chair.
6.    Eye level: 43-51 inches eye sight level depending on person’s height.

Of the six items I listed above you could quickly realize that the most important of these dimensions are the Armrest, Lap, Toe, and Eye level.
Armrest: From this position the arm reaches out in all different directions for the reach.
Lap: Imagine yourself utilizing a food tray on your lap and at the same time reaching for the TV remote control.
Eye level: Unlike an able body individual this is critical as many conditions have blocked views.
Toes: It is critical that toes do not extend much more than this so that the chair can engage an obstacle (a door for example) so that it can be pushed forward so that the person can gain access.

Disabled access wheelchair

Graphic #2: I ask you to look at the photo above and really form an opinion on whether or not this contraption looks all that mobile and or innovative?!

Observing this, an able-bodied individual has all his God-given abilities and can use his or her Arms extended straight ahead by bending his knees and then extending up to varying heights. Furthermore he doesn’t need his lap for a food tray as he can easily move over to a dining table or a high bar stool. And no matter what type of obstruction is placed in front of his sight, he can change his position to obtain the eye level he needs. Essentially then, it is clear but it’s worth saying again and again that there is no comparison between the able bodies mobility as compared to him sitting on a mobile chair. What is critical however and the point I wanted to make in this article is that, we as Architects pay very little attention to what these limitations are. It is only when you really think about the specifics of these limitations is when you can have an inkling of what needs to be done. As Architects we are good with dimensions, as long as we keep the specifics in mind, it would be easier to design or built spaces and environments that address these issues versus blindly following a set of standards that is written in building codes.

Actual manufacturer wheelchair dimensions

Graphic # 3:Actual manufacturer wheelchair dimensions

test test1

We briefly looked at the vertical dimensional challenges or obstructions that the person will face. Now let us get into the horizontal dimensions that are critical.
Comparing the graphic below to the dimensioned graphic above you will notice a slight discrepancy. This is where it gets a little interesting as you will realize that the Codes do very little to promote more space for wheelchair bound disabled individuals.

Disabled Access Wheelchair horizontal dimensions

Let us start with the seat depth and wheel radius:  If you look at graphic # 3 above you will notice that a typical seat depth is only about 16 inches. Graphic # 4 shows that the wheel radius behind the seat is 12 inches.
The person on the wheelchair cannot push his chair back against the wall. It may seem like nothing to an able-bodied person but it creates the rigid unchangeable back space that is unusable. Adding 12 inches (wheel radius) to 16 inches (seat depth), this places the knee caps at about 28 inches. Given that codes typically only require 48 inches total for depth of space, if you deduct the 31 inch radius (center of gravity shown above) the person has about a 10 inch area where you can extend past your knee caps!

Further looking at graphic# 4 you will notice that only a 17 inch radius is available to the person in a seated position. Essentially this clear shows that the person will not have access to a lot of things that are around him or her. In other words there is a lot reaching to get things.
Now let us look at the reach range that is shown on graphic # 4. First off its obvious limitation is the 31 inches radius. From a seated radius position of 17 inches to reaching position of 31 inches the gain is only 14 inches! That is as limited as a depth of a regular size book resting on a table. Further extension on a seated chair position will more than likely be painful or at the least very uncomfortable for most if not all wheelchair bound individuals.
The other thing to notice here is that this 31 inch radius is by no means a smooth transition. First off in a seated position even an able-bodied person cannot reach behind him by more than 45 degrees. A disabled individual loses most of that ability. Starting off from somewhere close to 180 degrees to the center of the wheel as his or her arm form the outside of the reach circle, the firs immediate obstruction is the wheel first and the arm rest ! Ever thought of that? Look at graphic# 3, it shows the dimension from armrest to armrest to be at the most 22 inches at the most. It becomes obvious that if a person grabs an item from his side and intends to bring to his lap or front view, each and every time he or she has to go over the armrest.
Please take note of the 17 inches to the center of gravity plus the 31 inches for the reach range that give the total of 48 inches. Most Codes point this out as a required total depth dimension of 48 inches. Now let us look at the width dimension of 30 inches. Again most Codes refer to these 30 inches as the required dimension. But wait! Let us go to graphic# 3 again so that we can see real wheelchair sizes. And let us compare that the graphic # 4. As it is shown in graphic # 4 if you take 7 inches on both sides for the wheels and the overall depth is supposed to be 30 inches, which only leaves the person a 16 inches wheelchair seat width. You should be able to see that we are asking for this person that is being sandwich between the armrests on a narrow seat to reach very rigidly to perform a function in a limited space, while if the reach radius in a seated position is 17 inches, then this depth in reality should be closer to 50 inches. And if the reach radius in an extended position is 24 inches, then this depth in reality should be closer to 78 inches.

So in short please pay attention to the specific dimension of real wheelchairs and compare them to what codes are asking you to do. Then put yourself in the position of the disabled person, sitting on the wheelchair, facing perhaps a routine day but knowing that the built environment is going to be challenging.  Whenever possible provide additional maneuvering room or more readily available futures of the space you are about to design.

Don’t forget as a Licensed Architect in California you are required to take at least five 5 hours of continuing education on disabled access.

You should leave me a comment!


Disabled Access Architect


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