DESIGN AND BUILD – TIMBER STAIRCASES

Basically a staircase consists of two sloping piect of timber, called strings, with treads fixed between them and a handrail. There is. however, a variety of ways in which these and other components are arranged and the form of the staircase will vary depending on the amount of space available and design of the house. The most common forms of timber staircase are the straight flight stair, the quarter-turn stair and the half-turn stair. Where there is a space between the flights of a staircase, it is called an open-well staircase.

The type of staircase you have and its method of construction will govern the type of repairs thai may be needed and whether you can do them yourself or need expert help.

Closed-riser staircases

Whatever form a staircase takes it will be con structed according to basic patterns in that it will be either a closed riser or an open-riser structure. Traditionally, the staircases found in most homes are of a cl er type and it is therefore worth considering the construction of this type of staircase at the outset, while remembering that many of its components are the same as those of open-riser staircases and that repairs can often be carried out in a similar fashion.

Treads and risers In a closed-riser staircase the horizontal treads are connected by vertical risers. with a tread and a riser together forming a step.

The protruding front edge of a tread is called a nosing; this usually has a rounded profile. Where the side edge of a tread is exposed a planted, or return, nosing is fixed. Usually the bottom step projects in front of the staircase and this step will be shaped in one of three ways. It may be a bullnose step, which is rounded, a curtail step, which is similar to a bullnosc step except it projects to the side as well as to the front of the staircase, or A splayed step, which is more angular in design. When a staircase turns there will be either a quarter or half-space landing. Where space is restricted taper steps or winders may be used. STRINGS Treads and risers are supported at each side by strings, which can take two forms: close strings and cut strings. Normally a string against a wall is a close string with the top and bottom edges parallel and the string deeply grooved to secure the treads and risers. The outer string may also be a close string or it may be a cut string with the lower edge of the string parallel with the pitch line or slope of the stairs, while the upper edge is CUT TO accept the treads and risers. Cut strings are common in older closed-riser staircases. but are not found so often in modern ones since they are more costly to construct.

With close strings the treads and risers are glued and wedged in position: if both strings are the close type, repairs can be carried out only from beneath the stairs – which may be difficult if the underside of the staircase is boarded over or plastered and in this case it may be better to call in a professional.

BALUSTERS These are the rails which give rigidity to the handrail and provide safety on the open side of the stairs. The balusters, and any infilling panels, together with the handrail and upper portions of the newel posts, form the balustrade.

NEWEL POSTS The outer strings and’ handrails are supported by newel posts at the top and bottom of the stairs; a newel post is also placed at even’ change of direction of a flight of stairs. Where a newel projects below a landing ceiling, the projecting portion, which is usually moulded or shaped at the end. is known as a newel drop. Half newels are often found on landings fixed to a wall to support the end of the landing balustrade away from the upper stair newel.

SPANDREL This is the triangular surface between the outer string and the floor; it may be panelled with wood or plasterboard or made of building blocks and plastered.

Carriage There may be other hidden components in the construction which can further complicate staircase repairs. For example, there could be a softwood beam, called a carriage, fixed below a flight where the width of the stairs is 900mm or more. Wood support blocks nailed to each side of the carriage support the treads. The bottom of the carriage beam is notched over a timber plate nailed to the floor and the top is fixed to a suitably placed supporting beam known as a landing trimmer or pitching piece. If the underside of the stairs is to be plastered, then beams similar to the carriage beam are fixed at cither side of the staircase.

When a close string staircase is fitted with a carriage, il is extremely difficult to replace treads or risers and such work should be left to the professional.

FIXING AND JOINTS Treads and risers are fixed into the grooves of close strings with adhesive and wedges are hammered home. With cut strings they are fixed with adhesive and nails and balusters are usually dovetailed to the treads, which may be given extra support with bearer blocks screwed to ‘.he inside face of the cut string. The exposed edge of long. On some stairs there are additional glued blocks to reinforce the joints between treads and strings.

Wall strings are fixed to the wall with screws and wallplugs. Outer strings are fixed to newel posts by tenons, which are usually secured with hardwood dowels: handrails are usually fixed in a similar way. Newels are mortised to receive the string and handrail ; tenons are notched and bolted to a floor joist at the stair base and to a trimmer joist on the landing. GEOMETRICAL STAIR This has a continuous outer string and handrail round an open well, tapered steps and newels at the top and bottom of the stairs; it is a complicated construction and all but the simplest, repairs should be left to a professional.

OPEN-RISER STAIRCASES

IN new houses and with conversions it is common to find open-riser stairs which are economical in their use of timber, take up a minimum amount of space and have an airy appearance which is ideal for open-plan layouts. These staircases do not have risers and the treads must be thicker than normal so they do not bend in use – they range in thickness from 38 to 50mm. Because it is difficult to carpet open-riser stairs apart from wrapping a short length of carpet round each tread, it is usual to use a timber which can be finished with a clear sealer. A hardwood such as mahogany may be used, or A strong, straight-grained softwood such as parana pine. Sometimes treads are made with a man-made board like plywood with an attractive hardwood for the outer veneer; usually the tread is finished with a hardwood lip.

With open-riser stairs in the home, close strings may be used although cut strings, with treads protruding beyond the strings, are more popular. Because of the size of the limber required, it is common for the strings to be made from laminated limber planks; these will look attractive when finished with clear sealer.

Sometimes the treads are mounted on hardwood blocks so the size of the timber required for the strings can be reduced. The blocks are filtcd, usually with hardwood dowels, to the lop edge of the strings, or screwed lo the inside face of the strings. Whichever method is used for cut string construction, the treads are normally fixed with adhesive and screws; the screw heads are recessed into the treads and covered with wood plugs.

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