How to Design and Calculate a Ramp?
We already know that the ramp, aside from its different design possibilities, allows—without forgetting the notion of promenade architecturale—its users to overcome physical barriers in the urban and architectural context.
Although it basically consists of a continuous surface with a particular angle of slope, it is necessary to point out the many constructive specifications, which of course may vary due based on the standards of different governing bodies. The following clarifications are intended to assist and determine the appropriate dimensions for comfortable and efficient ramps for all, based on the concept of universal accessibility.
To what extent can the slope of a ramp be modified? How can we determine its width and the space needed for maneuvering? What considerations exist regarding the handrails? Here we review some calculations and design examples for different ramps, below.
How is the Slope of a Ramp Calculated?
The slope can be expressed as a percentage that results from the ratio between the height to be overcome (h) and the length of the horizontal plane (d), multiplied by 100.
Slope expressed as a percentage = (h/d) x 100
From this expression, we can solve for the unknown values of each term. An existing ramp of 1 meter in height with a horizontal distance of 10 meters, will have a slope of 10%.
Accordingly, knowing the height to overcome on a project allows us to review recommendations for a slope consistent with the required needs.
A Schematic Example for an Outdoor Ramp
The recommended maximum slope for outdoor ramps can be established in relation to the height to be overcome and depends on the length of the plane. Based on averages and considerations from different countries -both regulatory and from manuals from Latin America—a slope of between 12-10% can, for example, be used only for very small heights, such as a step of up to 20 centimeters. As the heights require greater efforts, the slopes begin to reduce to reach recommendable values of 8% for heights of up to 50 centimeters; 6% for heights of up to 100 centimeters; 5% for heights of up to 150 centimeters; and 4% for ramps being used by the elderly.
In relation to the length of the ramp, for short distances—up to 1.5 meters—the slope should be less than 12%. For distances of up to 3 meters it must be less than 10%, and for distances of up to 9 meters, it should be less than 8%, always taking the above considerations regarding height into account.
The ramps should not have an excessive length without breaks—a maximum length of 9 meters—due to the efforts required to ascend without help in a wheelchair, or the force needed to transport heavy cargo.
An Example of the Calculated Distance Required (d)
As an example, to overcome a height of 54 centimeters, we will use a slope of 6%, which results in a horizontal plane of 9 meters.
6 = (0.54m / d) x 100
d = 0.54m / 0.06
d = 9 meters
A Schematic Example for an Indoor Ramp
Likewise, the percentages for the slopes of interior ramps allow for a 10% slope only to overcome very small heights, such as a step of up to 30 centimeters. Again, as the heights require greater efforts, the slopes are reduced to reach, for example, 8% for heights that go up to 75 centimeters; 6% for up to 150 centimeters; and 5% for the elderly.
Regarding the length of the ramps, for short distances—up to 3 meters—the slope should be less than 10%. For medium distances—between 3 and 6 meters—the slope should be less than 8%, and for distances between 6 and 9 meters, the slope must be less than 6% (also taking into account the previous recommendations regarding height).
Example of Calculated Distance Required (d)
To overcome a height of 90 centimeters, we will use a slope of 6%, which results in a 15 meter horizontal length.
6 = (0.9m / d) x 100
d = 0.9m / 0.06
d = 15 meters
Frequently Asked Questions
What shape/form must the ramp have?
The lengths of ramps must always be straight, as curved ramps make it difficult for the movement of a person in a wheelchair; in reference to this, the transverse slope of a ramp should also not exceed 2%, thereby avoiding any lateral slippage. In addition, it must be taken into account that with each change of direction, there must be a horizontal plane of at least 150 cm in diameter—a measurement that allows the 360 ° rotation of a wheelchair.
At their ends, ramps must have another horizontal plane of a minimum of 150 cm in diameter, free of obstacles and not impeded by the opening of doors. A person in a wheelchair cannot perform the opening maneuvers while sitting on the slope of the ramp.
What considerations exist for handrails?
Ramps must have continuous handrails—without interruptions—along their entire length, on both sides, and with different heights, ideally one between 65-75 cm and another between 90-100 cm. In addition, it is necessary that the handrails extend at their ends more than 30 centimeters so that anyone can reach it from the horizontal plane. They must be built in a fixed position and with smooth materials that don’t change with temperature variations (imagine a handrail exposed to the sun throughout the day or in areas that experience freezing temperatures).
Leaving aside handrails, we can’t forget that there is also a protective element on the perimeter of the ramp that exists to avoid any accidents on the clear edges, both by the sliding of wheelchairs, baby carriages, canes, or to warn people with reduced visual capacity.
How do we determine the width of a ramp?
Depending on local regulations, we find recommendations that range from a clearance width between handrails of at least 120 centimeters, as it comfortably allows the passage of a wheelchair and enables anyone to hold on both sides and a minimum clearance width of 180 centimeters for public spaces. In cases where a ramp width exceeding 180 centimeters is required, it would be appropriate to place an intermediate handrail that meets the above requirements.
When determining the width of a ramp, it is important to consider the maneuvering space of both a person with a wheelchair and a person with a baby carriage, mainly as a function of the intermediate breaks.
What materials can be used to construct a ramp?
Outside of any material used for the structure, the finishing materials of the ramp should use those that result in a hard non-slip surface that can be used in dry or wet conditions.
In addition, at the beginning and end of the ramp the horizontal surface there should be a tactile pavement, with different colors extending along the entire width of the ramp, to serve as a warning for people with reduced visual capacity. This same type of prevention should highlight the perimeter where the ramp opens, up to at least two meters clear of the passage.
We want to clarify that what is presented in this article is auxiliary information for the design of a ramp. All considerations for the construction of a ramp should always consider the specific characteristics of each project and should be prepared after evaluating the local regulations and according to the decisions taken by architects and/or professionals in the area.