Wooden stairs of the commonest description are thus constructed.2
Two "strings," SS, are fixed at the slope determined upon for the stairs; in these rectangular notches are cut, each equal in depth to the rise, and in width nearly equal to the tread of a step: upon these boards are nailed, forming the treads, t, and risers, r. Cut and Mitred Strings. - In stairs of a better description the outer strings are cut as above described; but the ends of the risers, instead of coming right through and showing on the outer surface of the string, are mitred against the vertical part of the notch in the string, as shown at aa in Fig. 217, the other end of the step being, as before, housed into a groove formed in the wall string.
1 Sc. Stringers. 2 Stairs of this construction are never used in ordinary house-building.
The outer extremity of the tread is also cut and mitred, as shown in Fig. 217, to receive a return moulding, forming the nosing of the end of the step.
BB show the mortises for the balusters, which should be dovetailed into the treads ;l the dovetails may be formed as at x or as at y, Fig. 218.
In many staircases the strings, instead of being notched out to receive the steps, are left with their upper surfaces parallel to the lower, and grooves are cut into their inner sides to receive the ends of the treads and risers; these grooves are called "housings," and the steps are said to be "housed" into the strings.
Fig. 219 is an elevation of the inner side of a housed string, showing the sinkings or housings formed to receive the steps.
Fig. 216. Elevation. Scale, ½ inch = 1 foot.
Fig. 217. Plan. Scale, ½ inch = l foot.
Scale, ½ inch = 1 foot.
Fig. 218 is a sectional elevation through the steps, showing the treads, t, and the risers, r, in position. These are secured by means of wedges, x y, which should be well covered with glue before insertion.
1 In speculative work the ends of balusters are simply skew-nailed to the treads or let into them without dovetailing, so that the balusters simply hang from the handrail.
The treads are sometimes formed with two tenons at each end, which fit into mortises cut through the string.
Open Strings are those, such as the cut strings, or cut and mitred strings, described above, which are cut so as to show the outline of the steps.
Close Strings have their upper and lower surfaces parallel, the steps being housed into them as above described (see Fig. 218).
The Wall String is the string up against the wall, and plugged to it. WS, Fig. 225.
The Outer String is the string at the end of the steps farthest from the wall. OS, Fig. 225.