staircase construction – design – building

Staircase constructionTraditionally, staircases were built on the spot by master carpenters working on the staircase construction of the house. Staircase construction has long been discontinued. Instead staircases are supplied to the site as factory-made units. Usually the staircase is fitted in the hall, with one side against a wall and the other side open. The part of the stair on which you actually walk is the tread, and the vertical timber that closes the gap between two treads is the riser. The riser is usually merely butted up to the treads and fixed by screws or nails. A better but rare practice, however, is for the riser to be joined by means of tongues and grooves. Sometimes too, a length of molding is fitted to the top of the riser, just underneath the projection of the tread, to mask any gap that may develop as the wood shrinks. The front edge of the tread – the nosing – is usually rounded off. Some modern staircases are of an open-tread design – to make it seem less bulky in the confines of the hall of a small house. It is dangerous to attempt to convert a conventional staircase into an open-tread one, however, for structural reasons. At each side of the staircase is a long length of timber, called a string. Two types of string are found — open and closed. An open string has a cut-out profile, into which the treads and risers are fitted.

A closed string has straight edges, and the treads and risers fit into grooves cut into its side. Wedges are fitted to hold the tread and riser tightly in the groove. The two strings in a staircase construction need not necessarily be of the same type. It is not uncommon for the wall string (the one against a wall) to be closed, and the outer string (the one away from the wall) to be open. A safety barrier or balustrade (also called a banister) is fitted to the open side (or sides) of a staircase. The length of timber which you hold as you climb a stairway is a baluster rail and the large upright members into which the baluster rail joins at each end are newel posts. The rail is supported by uprights known as balusters. Modern staircases have fewer balusters than older ones, but you should never alter the number of balusters, because you risk weakening the structure. A balustrade can also be fitted to the landing, if required. When a staircase has a wall on both sides, there is no balustrade,  but instead a handrail is fitted to the wall by means of metal brackets. Underneath, the staircase construction is supported on lengths of timber on edge known as carriages. There may be just one central carriage, or there may be an additional two to one near each edge. Lengths of timber, called brackets or sometimes cleats, are fixed to the carriages, to give extra support to the treads. In addition, triangular pieces of wood, known as glue blocks, are fixed to strengthen the join between tread and riser.

stairs_exteriorIn many small houses it is customary to have a cupboard under the stairs. In some instances, the underside of the staircase construction is in full view from within the cupboard. More usually, however, the underneath is covered with either plaster (plasterboard in modern homes, lath and plaster in older ones) or some form of board, such as hardboard.  The floorboards will need at least six months to dry out thoroughly. While they are moist they could damage synthetic floor coverings, such as vinyl a. In the meantime, use a temporary covering, or use a natural material such as cork, which would be immune to chemical attack. It has been suggested that lining a floor with hardboard will give sufficient protection, so you could lay any floor covering you like on top of it, but in fact the woodworm killer is so penetrative that it will work its way up through the nail holes and stain the top of the hardboard.