It is surprising how many times one sees steps that have not been constructed correctly; that is the risers have been built and then the tread is merely planted on top of them. This is not only bad practice but is aesthetically unattractive and gives the impression of inferior workmanship. Step treads should always be built in to the masonry surrounding them, once the first riser has been constructed and the flag stone that is to form the first tread has been placed then the second riser can be built. This second riser must catch the flag of the first tread by at the very least four inches (100mm), at this point if the steps or stairway is to be in a stair well or have wing walls then these side walls should also be constructed on top of the treads. By repeating this process step after step you will ensure the steps look right and the treads will not move or come loose as the whole stairway, treads, risers and side walls are integral to each other . This technique is relevant equally to mortared and dry stone walling but more so to the latter as obviously there is no mortar to cement the treads in place.
This rule also applies to stone seats built into recesses, sills in alcoves, in fact anywhere a slab is to be fitted into any adjacent stonework. It is also worth noting some basic dimensions for steps and stairways. Risers should ideally be within the range of five inches ( 125 mm ) to eight inches (200 mm ) for comfort and treads of between eight inches (200mm) and 14 inches (350mm). Outside these dimensions steps can feel awkward to use particularly when a long tread and a short riser is used. On longer flights when a step can be widened to form a landing then a width of three feet (900 mm) to four feet (1200mm) feels most comfortable. Obviously these dimensions are just intended as a guide or starting point and need to be adapted to suite individual applications but it is good to have a basic understanding of what works well.
Next time I will be dealing with the contentious subject of coursed work verses random, which side are you on!