This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
The plan (a) and the elevation (5) of a half-turn platform stairway, with a continued hand rail around a 7-inch cylinder, is shown in Fig. 21. This kind of a stairway is easy of ascent, breaking the flight, as it does, with a roomy platform, and allowing space for a window to light the stairway and hall from above the platform, while below it affords room for a doorway to the outside. With the last mentioned purpose in view, the soffit of the platform must not be less than 7 feet in height. The plan indicates also the timber framing of the well hole and platform. A jib panel F is shown at the start of the stairway in the elevation (b), the object of which is to close and neatly finish the angular space formed by the intersection of the stringer and the floor. The height of the jib panel is such as to receive the hand rail of the basement stairway. Where it is desired, the latter stairway may be enclosed by a paneled or lath-and-plaster partition extending up to the stringer of the upper flight.
The hand rail on the flight is 2 feet 2 inches in height from the center of the short baluster at the top of the step to the bottom of the rail; along the hallway the bottom of the rail is 2 feet 6 inches from the floor. These heights are based upon the commercial custom of turning ordinary pin balusters in lengths of 2 feet 4 inches and 2 feet 8 inches, 1 inch being allowed for entering the hand rail and 1 inch for the dovetail entering the tread, thus leaving the exposed part the length mentioned.
This kind of platform stairway can be altered in various ways, without changing the number of risers. For instance, a step can be taken from the upper flight, and added to the lower flight, increasing the run 9 inches and raising the platform one riser, making it 7 feet 11 inches. Then the well hole for the same headroom must be 9 inches longer, and the beam at the landing of the short flight must be brought forward the same distance. On the other hand, a step may be added to the short flight, making 4 risers in the short, and leaving 12 risers in the long flight. The well hole can now be shortened 9 inches, and have the same headroom as before; but it will be necessary to move the landing beam of the short flight back 9 inches, to accommodate the additional step. The platform, however, is one riser lower, making it 6 feet 8 inches; but if the total depth of the platform can be made 6 inches, thus reducing its depth 4 inches, the height to the soffit of the platform will be 7 feet.