Stairs and Ramps. Design and Calculations Unit Standard 24389 Calculation Guide

1. Stairs and Ramps. Design and Calculations Unit Standard 24389 Calculation Guide

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

3. 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

4. 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) 7 6 5 1200 4 3 Now we know that each riser is 171 mm.( 171 X 7 = 1197) 171 2 1

5. 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

6. Total rise 2660 Restricted going 3650 A formula to achieve this is No. of steps =(2x total rise+ total going) ÷ 600 Minimum gap to door 400mm 2660 3650

7. Total rise 2660 Restricted going 3650 A formula to achieve this is No. of steps =(2x total rise+ total going) ÷ 600 Total rise 2660 Restricted going 3650 No. of steps =(2x total rise( 2660)+total going)(3650) ÷ 600=14.95 ( try 15) So 2660 ÷ 15= 177.33mm (step height).

8. So now we know that we have 15 steps 177mm high Minimum gap to door 400mm 2660 3650

9. The going can now be worked out with the formula going = 600 –( 2x rise) Or 600- (2x177) = 246 Total going = 14 x 246= 3444 Less than 3600 so this will work Minimum gap to door 400mm 2660 4000 – 400 = 3600

10. Note that there are is one more riser than treads.