Staircases are often taken for granted yet they are complex pieces of carpentry which give many years of trouble-free use. They rarely need replacing: just as well, since they are often tailor-made to fit. Even so you can buy ready made versions, which cater for common storey heights and these can often be easily adapted to fit exactly.
A staircase comprises a number of steps fixed between two long boards which are fixed to the joists of the floors they connect. These boards are called strings, the horizontal surfaces of the steps are called treads and sometimes they have vertical boards between them known as risers.
Strings can be in two forms: closed and cut. With the former the ends of the treads and risers are housed in shallow slots cut in the face of the string and held there by wedges driven in from behind and below. The risers are fixed to the treads below with housing joints or screws, and to the treads above by triangular blocks glued and nailed in place. The top edge of a cut string is shaped to provide horizontal ledges to which the treads are fixed. Sometimes both foul’s of string will be used in the same staircase, the closed string being fixed against a wall with the cut string on the outside.
Further support for the steps can be provided by a beam that runs below the treads and risers parallel to the strings. This is known as a carriage.
There are two basic types of staircase: the closed tread and open tread. Of the two, the former is most common, having treads and risers in a boxed-in construction. The underside of the strings are usually clad with lath and plaster or gypsum board or there may be a closet below the stairs. The latter is preferable since it allows easy inspection and repair. The open tread staircase has no risers and is completely exposed.
In a closed tread staircase the treads are about lin thick and will overhang the risers by a similar amount, their leading edges or noses being rounded off. A decorative molding is often fitted below the nose. An open tread staircase will tend to have thicker treads because they are not supported by risers, although sometimes a batten will be set on edge immediately below them to stiffen the tread.
All staircases must have at least one handrail and if wide they must have one on each side, depending on the requirements of your local code. The handrail forms part of the balustrade, the other parts of which are the newel posts and balusters.
The newel posts fit at each end of the stairs with the handrail running between them. Not only do they support the handrail but often the strings as well which will be slotted into them and fixed with wooden dowels. Further support for the handrail is provided by the balusters which fit between it and the strings.
Though straight staircases are common, where space is limited it is often necessary for the stairs to change direction on the way up. A small quarter landing is used to provide a 90° change of direction and a half landing will turn the stairs back on themselves.
If there is not room for a half or quarter landing a turn can be put into the stairs by inserting triangular treads called winders. Winders are also used in spiral staircases which can be great space savers. Unfortunately they are not very practical since carrying furniture and other bulky items up them is difficult.