Notes on bar spacing and design for wrought iron railings, and Juliet balconies
Added this video to help explain the waffle below.
There are no rules on bars spacings or gaps between bars on railings, with the exception of Juliet balcony railings, patio railings and stair railings (these are 100mm gap maximum as they should comply to building regulations)
Bar spacing are very important part of any design. A railing that is 1220mm (4ft) with bars centres every 4 inches (102mm) is fine, it works. In that the gap from the wall to the first bar is same as the gap from the first bar and the second bar. In other words it looks nice and uniform, its evenly spaced.
Now assume the panel is 1270mm long (4ft 2inches), that spacing of 102mm (4inches) starts to fall apart, The gap from the end to the first bar is larger than that of the rest. It no longer has that nice uniform look
The alternative, add in an extra bar, but that still has the same problem as the previous one, the gap at the end is still different, its now smaller but smaller looks better than larger. Fine for mass produced railings available on the internet. but does not look quite as good as it should.
Assuming that you have two railings, one panel is 1220mm and the other panel is 1270mm, if these panels sit next to each other on a wall, they are going to look very different because of the extra bar.. It may have created an additional problem, if the railing has a design pattern to it, one has a centre bar one does not. If the design pattern was created from the centre bar which is often the case. it really has caused a problem.
To do it right you really are left with one alternative, change the spacings on the bars. On the 1270mm panel increase the bars spacings by 4mm, so instead of 102mm apart they are now 106mm apart. No one is going to notice the difference of a few millimetres in bar spacings, and you have two panels that will look exactly the same.
If you are using preformed parts in the railing design, like circles or scrolls, they no longer fit, if you adjust the gaps. There are plenty of pre manufactured parts that can be “bought in”, mass produced scrolls and circles. Trouble is they come in limited number of sizes, usually made to fit a gap of 90mm, 100mm and 120mm, SO changing bar gap sizes now means they are no longer of use, and the only option is to make them by hand, which is not as cheap as the mass produced option.
An option for reducing the price is to increase the gap between the bars. At 102mm centres (90mm gap between bars if using 12mm uprights) a 6ft long railing will have 17 upright bars. At a spacing of 152mm centres (140mmm between bars) that has now reduced the bar count to 11. Obviously that means less material, less labour, less paint So can be a way of saving money.