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

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

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.

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 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 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).

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) = 246 Total going = 14 x 246= 3444 Less than 3600 so this will work

Note that there are is one more riser than treads.

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