How to Measure Sloping Ground

The Americans with Disabilities Act (ADA) requires wheelchair ramps to have a slope no steeper than 1:12 so that people in wheelchairs can go up and down without assistance. This means that for every inch of rise in the threshold, the wheelchair ramp must be 12 inches (one foot) long. For example, a door threshold height of 25″ requires a 25′ ramp along with a 5’ x 5’ threshold platform. Any threshold that is more than 30″ off the ground requires at least one resting platform in the middle of the ramp to break it up. Why? Because the ADA requires a resting platform for every additional 30′ of ramp run. Therefore, if the threshold is 32″ high, one resting platform is required; if the threshold is 62″ high, two resting platforms are required.

What you will need:

• Stakes
• String or twine
• Hammer
• Line level
• Tape measure

Why is it important to measure?

In a perfect world, every construction site would be completely flat, but all site workers know that is not the case. Therefore, ground slope measurements are required to make sure that the slope of the handicap ramp is accurate. If the ground is sloping upwards from the door threshold, the ramp will likely require less ramp material than if the ground is flat or sloping downwards. This typically means that the ramp will be less expensive if the ground is sloping upwards and more expensive if it is sloping downwards.

Diagram 1The 30" threshold height correlates to a 30' ramp because the ground is neither sloping upwards or downwards; it is completely flat.
Diagram 2On the left side of the building, the ground is sloping upwards, which means that the 30" threshold will require a ramp that is less than 30'. On the right side of the building, the ground is sloping downwards, which means that the ramp will have to be longer than 30'. It will also require a resting platform in the middle of the ramp that will add an additional cost. A resting platform is required for every additional 30' of ramp run.

Where to measure:

Slope measurements need to be taken where the wheelchair ramp will sit, so you will first need to figure out the best layout. To determine the best layout:

1. Measure the height of the door threshold
2. Determine the required ramp length
1. For every inch of rise, a foot of ramp run is needed (i.e. door threshold height = 20”, so ramp run = 20’)
2. Make sure to account for the required 5’ x 5’ platform at the door threshold
3. Remember, for every additional 30′ of ramp run, an additional 5’ x 5’ resting platform is required
3. Note any obstacles or space limitations
4. If there are no obstacles or space limitations, the ramp layout does not matter; choose the preferred layout
5. If there are obstacles or space limitations, a switch back ramp or L-ramp would be best
6. If there are two buildings side-by-side, a common platform ramp could be used to maximize space utilization

Once the layout is determined, measure the ground slope every 10′ in the direction(s) that the ramp will travel. To measure an L-ramp, measure from where the threshold platform would sit to where the first platform would sit in increments of 10′. Then measure from the platform down to where the ramp would end.

Types of Ramp Layouts

How to measure:

1. Roughly mark the area on the ground where the 5’ x 5’ door threshold will sit
2. At the edge of the outline, put a stake in the ground, and tie a string to it at the base
3. Walk 10 feet in the direction that the ramp will travel, and put another stake in the ground
4. Tie the same string from the first stake to the second stake, making sure it is taut
5. Place a line level in the center of the string
6. Move the string around the second stake either up or down until the line is level
7. Measure the distance from the ground to the string on the second stake to determine the slope
8. Repeat every 10′
Where to Place Stakes
Calculating Slope

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