In the UK most spiral staircase kits use vertical spindles in their guard rail designs. It is important to ensure you use the correct spacings between spindles so that the railing can be used safely. The building regulations state that there should not be a gap greater than 100mm between spindles. To make calculating the number of spindles straightforward, and to comply with the regulations, we use a gap of 99mm maximum for our examples below.
The first thing to check is the diameter (width) of the spindles you will be installing - for example a Gamia spiral staircase has spindles 22mm diameter, and an Artemis spiral staircase has 21mm diameter spindles.
For our calculations we are using a spindle width of 22mm and a max spindle spacing of 99mm
Firstly, measure the length of the gap that you wish to fill with your guard rail or balustrade.
Next, deduct 99mm from your total measurement. Then divide the result by the width of a spindle plus the maximum spacing allowed. For example, if your balustrade is 1250mm long, and spindle spacing is a maximum 99mm, and spindle width is 22mm, the formula would be (1250 - 99) divided by 121mm (which is your 22mm spindle plus 99mm spacing) = 9.5 spindles. This is then rounded up to the next whole number, 10. So in summary you need 10 spindles to fill a balustrade length of 1250mm.
To give the best aesthetic results you should space the spindles equally in the run of balustrade - they don't need to have the same spacing as on the spiral staircase, by the way. Simply multiply the width of each spindle by the number of spindles in the run, in our example this is 10 no. Subtract the result from the total length of the run of balustrade.
The calculation in our example is; 10 x 22mm diameter = 220mm, where 10 is the number of spindles and 22mm the width of each spindle 1200mm minus 220mm = 980mm, the total space left.
If you divide the result, 980mm, by the number of spindles you get 98mm which in this example gives equal spindle spacing and also complies with the building regulations.
As previously noted other spiral staircase brands will use different spindle sizes so don't forget to adjust the calculations for the brand of spiral staircase you are installing.