This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The following are the technical names for the parts of stairs: - "Flight" is 1 the term for one continued series of steps without any break; " landing " is the level flat between two flights; " tread " is the horizontal surface of a step; " riser " is the vertical part between 2 steps; " winders " are the winding steps round a curve when there is no landing.
The convenience of stairs is largely dependent upon the proportioning of the height ] of riser and width of tread. Blondel's rule, which adopts as a module of measurement the length of a man's pace walking leisurely on level ground, or 2 French feet = 25 ■ 56 in. English, and assumes that every 1 in. of ascent is equal to 2 in. of progress, is a correct theory within certain limits only. The energy expended by a man in lifting himself 40 ft. up a ladder nearly vertical is vastly more than twice the energy required to advance 40 ft. on a level plane. This is sufficient to show that the rule is only correct when the rate of ascent is moderate. Probably, an English architect, working out the same theory, would have adopted 2 English feet or 24 in. as his module. Corson takes the mean (nearly) of these two, or 24.75 in., as being a reliable guide to an easy stair suitable for houses of moderate size.
The height of riser, which should not be exceeded, he fixes (by experience) at 6 • 75 in., deducting twice this, or 13.50 from 24.75, we have 11.25 for the breadth of tread. (Blondel's rule would give 12.06, which would be found too broad for that height of riser.) Of course, the breadth of tread is from riser to riser, disregarding torus or moulding, if there is one. Obviously the experience of short and tall people will differ somewhat. Also it is necessary to consider the length of the step: the longer the step, the broader should be the tread.
Again, for steps outside, leading up to the doorway or a terrace, decrease the riser and increase the tread; how much must be matter of judgment with the architect, according to the number and length of steps and character of house. Terrace slopes ought to be 3 to 1. To suit that slope, steps of 5.10 in. rise and 15.30 in. tread would be a fit dimension, and would agree with Blondel's formula. There is, however, for stairs generally, another and very simple rule, namely: Keep the slope of the stair to 30°, or as little over that angle as possible. A step of 6 3/4 in. rise would in that case have a tread of 11 5/8 in.; but it would be better to have less rise and less tread, say 6 1/2 in. and 11.20 in. It is needful to have in mind old people and children, to whom a low riser is of great moment.
When the size of the house will not allow the use of such proportions as are given above, diminish the tread rather than increase the height of the riser. Blondel's rule becomes absurd when followed out, and the stair becomes a step ladder, as when you find steps 8 in. tread and 9 1/2 in. rise, making breakneck stairs. The minimum width of tread may be called 9 in. It is too little, but sometimes economy of space compels it, and if only the riser be kept to the maximum of 6 3/4 in., the stair will be reasonably easy and safe. There are exceptions to every rule, and it will be found that the steps of a turnpike stair winding round a 6-in. or 8-in. newel, must deviate from the proportions given above, i.e. when measured as winding stairs usually are, at the centre of the length of step. The head room must be preserved at all costs.
With regard to the planning and sotting out of stairs, a volume might ho written, and illustrations given without end. The staircase often is, and oftener might be, tin-most picturesque feature of the interior of a house; most often it is so treated that it would be best hidden away out of sight. A stair in 2 flights, with narrow well-hole, offers the least opportunity for effective design; a wide well-hole removes the difficulty, and with a stair in 3 flights almost anything may be done. A stair with the first (light (only) between 2 walls, and then opening out to the double width, is capable of beauty and picturesque treatment. Stairs with winders are not desirable, but sometimies are unavoidable, and very well adapted for warehouses when planned with a well-hole, say, 20-30 in. wide. The winders should radiate, not to the true centre, but to a centre removed half a step or so farther back from the string; thereby the narrow ends are made wider and the ramp of the handrail is improved. The arrangement of a central stair and 2 side flights should only be used on the grand scale and in buildings of palatial character.
In houses of less importance, either it will be cramped in dimensions, or it will be too large for the house, and out of keeping and pretensions.
A convenient height for the handrail of a stair is about 3 ft. from the surface of the treads. The upper surface of it should be semicircular and about 2 1/4 in. diam.; it should be continuous, without break of any kind from top to bottom of the stairs. The "balusters" which support the handrail are sometimes also intended to fill up the space between it and the stairs, so as to prevent any one falling through. When for the former object only, as is generally the case in barracks, the fewer balusters there are the better, as they are very liable to injury and so cause expense in repair; for this reason it is better to have a few strong posts well framed into and connected by iron straps with the bearers of the stair. In private houses, where the balusters are generally required to fill up the space, the ordinary practice is to make them square wooden bars of small size, and to place iron balusters of the same size at intervals to strengthen the whole structure. But in all public buildings, especially in military buildings, it is desirable to use balusters of a much larger size, and more firmly fixed to the stairs, and at just sufficient interval to prevent children falling through.
The construction of the steps is illustrated in Fig. 1419 : the tread a, say 10 in. broad and 2 in. thick, is supported by the riser b of the same thickness and about 7 in. high, a " blocking " or "rough bracket" c being placed underneath the tread and behind the riser, the ends being dovetailed or notched into the face of the "outer string." The outer string is the woodwork flanking the side of the stairs not next the wall. In front of the riser, and occupying the corner formed by it with the front edge of the tread, is a moulded fillet d; the rounded edge of the tread e is termed the nosing.