Figure 6-15.—Unit rise and run.are cut from solid pieces of dimensional lumber (usually2 by 12s) and are called cutout, or sawed, stringers.STAIRWAY LAYOUTThe first step in stairway layout is to determine theunit rise and unit run (fig. 6-14, view B). The unit riseis calculated on the basis of the total rise of the stairway,and the fact that the customary unit rise for stairs is7 inches.The total rise is the vertical distance between thelower finish-floor level and the upper finish-floor level.This may be shown in the elevations. However, sincethe actual vertical distance as constructed may varyslightly from that shown in the plans, the distance shouldbe measured.At the time stairs are laid out, only the subflooringis installed. If both the lower and the upper floors are tobe covered with finish flooring of the same thickness,the measured vertical distance from the lower subfloorsurface to the upper subfloor surface will be the same asthe eventual distance between the finish floor surfaces.The distance is, therefore, equal to the total rise of thestairway. But if you are measuring up from a finish floor,such as a concrete basement floor, then you must add tothe measured distance the thickness of the upper finishflooring to get the total rise of the stairway. If the upperand lower finish floors will be of different thickness,then you must add the difference in thickness to themeasured distance between subfloor surfaces to get therise of the stairway. To measure the vertical distance, usea straight piece of lumber plumbed in the stair openingwith a spirit level.Let’s assume that the total rise measures 8 feet11 inches, as shown in figure 6-15. Knowing this, youcan determine the unit rise as follows. First, reduce thetotal rise to inches-in this case it comes to 107 inches.Next, divide the total rise in inches by the average unitrise, which is 7 inches. The result, disregarding anyfraction, is the number of risers the stairway willhave—in this case, 107/7 or 15. Now, divide the totalrise in inches by the number of risers-in this case,107/15, or nearly 7 1/8 inches. This is the unit rise, asshown in figure 6-15.The unit run is calculated on the basis of the unitrise and a general architect’s rule that the sum of the unitrun and unit rise should be 17 1/2 inches. Then, by thisrule, the unit run is 17 1/2 inches minus 7 1/8 inches or10 3/8 inches.You can now calculate the total run of the stairway.The total run is the unit run multiplied by the totalnumber of treads in the stairway. However, the totalnumber of treads depends upon the manner in which theupper end of the stairway will be anchored to the header.In figure 6-16, three methods of anchoring the upperend of a stairway are shown. In view A, there is acomplete tread at the top of the stairway. This means thenumber of complete treads is the same as the number ofFigure 6.16.—Method for anchoring upper end of a stairway.6-12

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