What a ramp has to be, and whether it fits RAMP

“One in twelve” is the steepest of three, not the answer

The rule people carry in their heads is a single number, and the guidance is not a single number. What it says is that the gradient allowed depends on how long the flight is, because a long push at a shallow angle and a short push at a steep one are different amounts of work for the person doing the pushing:

• a flight going up to 10 m may be 1:20, rising 500 mm
• a flight going up to 5 m may be 1:15, rising 333 mm
• a flight going up to 2 m may be 1:12, rising 166 mm

So 1:12 is not the rule; it is what you are allowed for a short flight only. A design drawn at 1:12 for a rise of 600 mm is not a steep ramp that complies; it is a flight four times longer than 1:12 is permitted for.

The landings are what people forget

A ramp is not one slope. It is a series of flights with landings between them, and the landings are usually discovered after the levels are set and the space is gone.

A rise of 900 mm at 1:15 is not one slope of thirteen and a half metres. It is three flights of 300 mm each, with a landing between each pair and one at the top and the bottom. Those landings are flat, they have a minimum length of their own, and they have to go somewhere. The total run is the sum of the flights plus the landings, and it is substantially more than the number you get by dividing the rise by the gradient.

That difference is the single most common reason a ramp is redesigned late: the arithmetic was done on the slope alone, the space was allocated from that, and the landings had nowhere to go. Work out the whole run before you commit to where the ramp starts.

What the arithmetic does not settle

Getting the gradient and the landings right is necessary and it is not the whole design. Still to think about, and all of it on the ground rather than on the page:

The approach and the turn. A landing at the top has to be big enough to turn on and to open a door from, and a door that opens outward over the landing takes that space away.

The handrails, on both sides, continuous past the ends, at the heights the guidance gives, and the edge protection that stops a wheel going over the side, which is a separate requirement from the rail.

The surface, which has to stay slip-resistant when it is wet, and the cross-fall, which drains the ramp and which is limited because too much of it pulls a chair sideways.

And the honest question underneath all of it: whether a ramp is the right answer here. A rise that needs four flights and three landings is a very long structure and often a worse solution than moving the entrance, regrading the approach, or fitting a lift. The arithmetic here is quick enough that you can find that out before anybody has drawn it.

This works it out in the tab and nothing is uploaded. Check the figures against the current edition of the guidance that applies where you are building, because the numbers above are the common ones and they are not the same everywhere. Nearby: FALL and EVACUATE cover the other side of getting people up and down safely, and LEVEL handles the setting out.