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Section 4 Finishing
the carpenter, who must have a thorough under-
standing of basic stair design and how to lay out
and make the installation.
All stairs, whether main or service, are
shown on the fl oor plans. When details of the
stair design are not included in the complete set
of plans, the architect usually specifi es on the
plan view the number and width of the treads
for each stair run. Sometimes, the number of
risers and the riser height are also included.
Working Knowledge
In a given run of stairs, be sure to make
all of the risers the same height and all of the
treads the same width. An unequal riser, espe-
cially one that is too high, may cause a fall.
18.5 Stair Calculations
To calculate the number and size of risers
and treads (less nosing) for a given stair run,
fi rst divide the total rise by 7 to determine the
number of risers. Some carpenters divide by 8.
Either number is accurate enough. For example,
if the total rise for a basement stairway is 7′-10″
(94″), dividing by 7 yields 13.43. Since there must
be a whole number of risers, round 13.43 to 13.
Divide the total rise by that number to deter-
mine the unit rise:
Total rise: Vertical distance from one fl oor to
another.
Figure 18-12. Architectural drawings show stair layouts. Note the information given for riser-tread ratios.