The most primitive stairs relied on footholds chopped into a log, the next stage was the ladder form, still used in adventure playgrounds (Figures 6.2a and 6.2b). Robust treads can be cut from quartered

Figure 6.1a Ladder steps made from planks, circa twelfth century, Norway logs and secured down to a carriage timber. Ships' ladders reveal considerable refinement with members whittled down to give the most efficient use of timber. Such construction is the prototype of today's open tread stairs (Figure 6.2c). The stability relies on effectively connecting the outer strings in the absence of overlapping rungs or treads of the more primitive pattern. The essential elements can be summarized as follows:

• Uncut strings to maximize longitudinal strength.

• solid plank or multi-ply treads with adequate glue line to mortices.

• Steel cross ties with plate bolt ends to tie the strings together.

• Refinements such as part risers will assist with the load-bearing quality of the treads. This will increase the glue-line and help comply with the National

Figure 6.1d Spiral stairs, called the Miraculous Stairs, built without nails, 1878, Our Lady of Light Chapel, Sante Fe, New Mexico

Figure 6.1c Elegant wooden flight reinforced by a wrought iron flitch within the strings (late eighteenth century), Stamford Assembly Rooms

Figure 6.1d Spiral stairs, called the Miraculous Stairs, built without nails, 1878, Our Lady of Light Chapel, Sante Fe, New Mexico

Building Regulations concerning the maximum 100 mm gap.

The width-to-span proportions are dictated by engineering and the economics of timber supply. Open tread flights are usually limited to a metre width and for runs up to 16 risers. The sizings given in Figure 6.2c are for domestic purposes, say 900 mm width x 14 risers.

Wider designs, up to 1800 mm, will involve carriage pieces with cantilever treads or a combination with steel brackets to fully support long span treads, shown in Figure 6.2d. Cut-string open stairs appear clumsy and present problems in effectively framing treads and

Figure 6.2a Framing timber stairs: Log pole with footholds chopped out, circa twelfth century, Norway
Figure 6.2b Framing timber stairs: Log ladder, circa twentieth century, children's playground

strings; such construction is more appropriate to composite assemblies. Narrow ladder-like steps are permitted in the UK for access to a single room, see Section 4.2.5 for details. Conventional framing relies on 'box construction' where a set of stairs is 'cased' together, hence the term 'staircase'. Mass production and preferred dimensions have ensured that costs are well below custom-made designs. Staircase kits from suppliers include a range of modules that come with all the ancillary details - newels, balustrades, handrailing and trim for platform treads and return nosings where cut strings are preferred. It is also possible to directly assemble dog-leg and multiple-turn flights from standard components. Figure 6.3 is a typical page from a manufacturer's cat-alogue.2 Compare that to the superior quality of profile where an experienced architect is involved, as with the replacement stair in Figure 6.4b. The newel post has a framing role in

Figure 6.2c Framing timber stairs: Details of open tread stairs

Figure 6.2d Framing timber stairs: Open treads with carriage pieces

conventional wood-framed stairs, it provides a bearing plane for flights and hand-railing as well as masking jumps in handrail alignment (refer forward to Figure 6.5e). In times past such work was entirely framed in oak enriched with carvings and statuary as at Hatfield House (Figure 6.4c), perhaps the finest Jacobean staircase in England. More comely versions exist in the Inns of Court and at the former offices of the Architectural Press in Queen Anne's Gate (Figure 6.4a).

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