Stairs and Ramps.Design and Calculations

Unit Standard 24389 Calculation Guide

Example 1A single flight of stairs must have a rise between 165 and 175. The total rise is 1200. Calculate a suitable rise and going.

1200

To calculate the rise for each step you need to divide the total rise by a number between 164 and 172 . We will choose 168.1200÷ 168 = 7.142

1200

Now divide 1200 by 7. This will give us a rise that will add up to exactly 1200.1200 ÷ 7 = 171.42 ( As the fraction of a millimetre is less than .5 we round down to 171)

Now we know that each riser is 171 mm.( 171 X 7 = 1197)

171

1

2

3

4

5

6

7

Sometimes the tread or going of the stair is restricted. We can design a suitable going in the same way that we designed the rise in the previous example

2660

3650

Minimum gap to door 400mm

Total rise 2660Restricted going 3650A formula to achieve this is No. of steps =(2x total rise+ total going) ÷ 600

Total rise 2660Restricted going 3650A formula to achieve this is No. of steps =(2x total rise+ total going) ÷ 600

Total rise 2660Restricted going 3650No. of steps =(2x total rise( 2660)+ total going)(3650) ÷ 600=14.95 ( try 15)So 2660 ÷ 15= 177.33mm (step height).

2660

3650

Minimum gap to door 400mm

So now we know that we have 15 steps 177mm high

2660

4000 – 400 = 3600

Minimum gap to door 400mm

The going can now be worked out with the formula going = 600 –( 2x rise)Or 600- (2x177) = 246Total going = 14 x 246= 3444 Less than 3600 so this will work

Note that there are is one more riser than treads.