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Stairway Layout
Stairway Construction

Builder 3&2 Volume 02 - Construction manual for building structures
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Figure 6-17.—Layout of lower end of cutout stringer. risers. For the stairway shown in figure 6-15, there are 15 risers and 15 complete treads. Therefore, the total run of the stairway is equal to the unit run times 15, or 12 feet 11 5/8 inches. In view B, only part of a tread is at the top of the stairway. If this method were used for the stairway shown in figure 6-15, the number of complete treads would be one less than the number of risers, or 14, The total run of the stairway would be the product of 14 multiplied by 10 3/8, plus the run of the partial tread at the top. Where this run is 7 inches, for example, the total run equals 152 1/4 inches, or 12 feet 8 1/4 inches. In view C, there is no tread at all at the top of the stairway. The upper finish flooring serves as the top tread. In this case, the total number of complete treads is again 14, but since there is no additional partial tread, the total run of the stairway is 14 times 10 3/8 inches, or 145 1/4 inches, or 12 feet 1 1/4 inches. When  you  have  calculated  the  total  run  of  the stairway, drop a plumb bob from the header to the floor below and measure off the total run from the plumb bob. This locates the anchoring point for the lower end of the stairway. As mentioned earlier, cutout stringers for main stairways are usually made from 2 by 12 stock Before cutting the stringer, you will first need to solve for the length of stock you need. Assume that you are to use the method of upper-end anchorage shown in view A of figure 6-16 to lay out a stringer for the stairway shown in figure 6-15. This stairway has a total rise of 8 feet 11 inches and a total run of 12 feet 11 5/8 inches. The stringer must be long enough to form the hypotenuse of a triangle with sides of  those  two  lengths.  For  an  approximate  length estimate, call the sides 9 and 13 feet long. Then, the length of the hypotenuse will equal the square root of 92 plus 132. This is the square root of 250, about 15.8 feet or 15 feet 9 1/2 inches. Extreme  accuracy  is  required  in  laying  out  the stringers. Be sure to use a sharp pencil or awl and make the lines meet on the edge of the stringer material. Figure 6-17 shows the layout at the lower end of the stringer. Set the framing square to the unit run on the tongue and the unit rise on the blade, and draw the line AB. This line represents the bottom tread. Then, draw AD perpendicular to AB. Its length should be equal to the unit rise. This line represents the bottom riser in the stairway. You may have noticed that the thickness of a tread in the stairway has been ignored. This thickness is now about to be accounted for by making an allowance in the height of this first riser. This process is called “dropping  the  stringer.” As you can see in figure 6-14, view B, the unit rise is measured from the top of one tread to the top of the next for all risers except the bottom one. For the bottom riser,  unit  rise  is  measured  from  the  finished  floor surface to the surface of the first tread. If AD were cut to the unit rise, the actual rise of the first step would be the sum of the unit rise plus the thickness of a tread. Therefore,  the  length  of  AD  is  shortened  by  the thickness of a tread, as shown in figure 6-17, by the 6-13







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