Johnson Level & Tool Mfg. RAS-1 User Manual
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The ideal inch rise is 7 or 8 (or 30° to 35°) but may be from a
5-inch rise to a 14-inch rise depending on the circumstances. The
step rise or run may be modified if the run becomes impractical
or if the minimum head room is under 6 1/2 ft. Check the head
room by measuring down along a plumb line dropped from the
lowest ceiling point to where the tread beneath would be. To find
the tread height, count the number of steps necessary to get
under the plumb line and then multiply by the step rise. Another
consideration is to have a minimum of 4" from the inside corner
of the step to the bottom edge of the stringer (See Figure 18). A
quick test is to use the square as you did for the common rafter
top plumb cut (using the step inch rise) and make a plumb line
the distance of the step rise, then measuring from the end of the
plumb line directly to the edge of the stringer.
The tread length depends on available room and intended use.
For instance, for two-way traffic a length of 36 to 42 inches is
needed, whereas one-way traffic doesn’t require over a 24 inch
length. Also, the calculated tread width does not include a nosing
width (1-3/4" being maximum).
FIG. 18 Stringer Layout.