I have been asked by a frustrated homeowner why his Kompact modular staircase kit has caused problems with his building inspector over the 50mm. minimum going on tapered stair treads rule.
Under the Building Regulations part K.1.18 tapered stair treads should have at least 50mm going at the narrow end. This refers to the triangular treads (winding treads) that are used to change direction on a flight of stairs. It cannot be applied to spiral stairs these are covered by alternative rules under BS 5395.
I have to confess that I have never seen the reason for this strange rule. I can only assume that the powers that be saw reason to maintain enough tread to stand on at the pointy end of of winding stair treads. In my ignorant and humble opinion this is not called for, A. you have no reason to walk there, and B. it is almost impossible to do so. You try it; I think you will agree. By the nature of the beast, I believe that you tend to automatically walk up the middle of a typical domestic stair winding treads. However for whatever reason the rules are the rules and we have to live them.
The problem that Mr frustrated homeowner has is fairly uncommon in this enlightened age. It all hinges on the difference between traditional staircases with stringers (wooden side supports) plus newel posts, and modern open plan staircases with centre spine supports and no newel posts. This second category covers all kit modular kit staircases such as the Kompact, Genius or Reflex.
With traditional staircases the newel post in the corner of the winder treads tends to cut the treads off short. that in turn tends to create the required 50mm going. However take away the newel post and continue the tread to a point as you do with a modern open plan kit stair, and you will have no going at all at the point. So it is really a question of where you measure to when you are talking about counts as the effective end of the tread.
Thankfully this is a rare issue, most inspectors are by now well versed in the ins and outs of modern open plan kit staircases, and realise that the taper detail meets with the spirit of this rule. Unfortunately Mr frustrated seems to have met the exception. Hopefully a little polite discussion will change things for the better.