The nose makes the tread more comfortable to climb in socked feet or bear feet. It mustn’t over hang too much or it becomes a tripping hazard. A nose is not an essential part of a tread. There are plenty of staircases, particularly more contemporary designs that are constructed without a nose.
Treads and Risers
25.4cm) is dictated by the average adult foot size, although it is not necessary to be able to fit your entire foot on a tread in order for walking up the stairs to be both comfortable and safe.
The riser height (max 7¾ins / 19.7cm) is limited by the way in which we come down the stairs. If you think about it, you could climb up far more than 7¾ inches very easily and you could climb down far more than 7¾ inches very easily if you are facing backwards. The rungs of a ladder are placed at more like 12ins / 30cm apart. But we go down the stairs facing forwards, and it’s this that limits the riser size to being much smaller.
The maximum dimension between balusters is 6ins / 15.2cm. I don’t know for certain what this is based on, but I’m thinking the idea is that it shouldn’t be easy to get a foot or arm trapped in between a baluster. Having said that there are plenty of staircase designs where the outer hand rail has bigger gaps or is absent altogether.
The diagram below indicates the minimum ceiling heights required. These are very much the minimum and a ceiling height approaching the regular ceiling height is more ideal.
The minimum staircase width is the same as the minimum circulation zone width of 3ft / 0.91m