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Stairs
Figure 6-17.Layout of lower end of cutout stringer.

Builder 3&2 Volume 02 - Construction manual for building structures
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Figure 6-15.—Unit rise and run. are cut from solid pieces of dimensional lumber (usually 2 by 12s) and are called cutout, or sawed, stringers. STAIRWAY LAYOUT The first step in stairway layout is to determine the unit rise and unit run (fig. 6-14, view B). The unit rise is calculated on the basis of the total rise of the stairway, and the fact that the customary unit rise for stairs is 7  inches. The  total  rise  is  the  vertical  distance  between  the lower finish-floor level and the upper finish-floor level. This may be shown in the elevations. However, since the actual vertical distance as constructed may vary slightly from that shown in the plans, the distance should be  measured. At the time stairs are laid out, only the subflooring is installed. If both the lower and the upper floors are to be  covered  with  finish  flooring  of  the  same  thickness, the measured vertical distance from the lower subfloor surface to the upper subfloor surface will be the same as the  eventual  distance  between  the  finish  floor  surfaces. The distance is, therefore, equal to the total rise of the stairway. But if you are measuring up from a finish floor, such as a concrete basement floor, then you must add to the measured distance the thickness of the upper finish flooring to get the total rise of the stairway. If the upper and lower finish floors will be of different thickness, then you must add the difference in thickness to the measured  distance  between  subfloor  surfaces  to  get  the rise of the stairway. To measure the vertical distance, use a straight piece of lumber plumbed in the stair opening with a spirit level. Let’s assume that the total rise measures 8 feet 11 inches, as shown in figure 6-15. Knowing this, you can determine the unit rise as follows. First, reduce the total rise to inches-in this case it comes to 107 inches. Next, divide the total rise in inches by the average unit rise, which is 7 inches. The result, disregarding any fraction,  is  the  number  of  risers  the  stairway  will have—in this case, 107/7 or 15. Now, divide the total rise in inches by the number of risers-in this case, 107/15, or nearly 7 1/8 inches. This is the unit rise, as shown in figure 6-15. The unit run is calculated on the basis of the unit rise and a general architect’s rule that the sum of the unit run and unit rise should be 17 1/2 inches. Then, by this rule, the unit run is 17 1/2 inches minus 7 1/8 inches or 10 3/8 inches. You can now calculate the total run of the stairway. The total run is the unit run multiplied by the total number  of  treads  in  the  stairway.  However,  the  total number of treads depends upon the manner in which the upper end of the stairway will be anchored to the header. In figure 6-16, three methods of anchoring the upper end of a stairway are shown. In view A, there is a complete tread at the top of the stairway. This means the number of complete treads is the same as the number of Figure 6.16.—Method for anchoring upper end of a stairway. 6-12







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