Chapter 18 Stair Construction
605
94″ ÷ 13 = 7.23 or 7 1/4″
Number of risers = 13
Riser height = 7 1/4″
In any stair run, the number of treads is one
less than the number of risers. A 10 1/2″ tread is
correct for this example. The total run is calcu-
lated as follows.
Number of treads = 12
Total run = 10 1/2″ × 12
= 126″
= 10′-6″
The stairs in this example will have 13 risers
7 1/4″ high, 12 treads 10 1/2″ wide, and a total
run of 10′-6″.
Since this example is for basement stairs, the
total run can be shortened by using a steeper
angle. To do so, decrease the number of risers
and shorten the treads. The calculations are:
94″ ÷ 12 = 7.83 or 7 5/6″
Number of risers = 12
Height of risers = 7 5/6″
Number of treads = 11
Tread width selected = 9″
Total run = 9″ × 11″
= 99″
= 8′-3″
Some manufacturers supply tables for deter-
mining rise and run, riser, and tread ratios. See
Figure 18-13.
18.6 Stairwell Length
The length of the stairwell opening must be
known during the rough framing operations.
If not included in the architectural drawings, it
can be calculated from the size of the risers and
treads.
It is also necessary to know the headroom
required. Add to this the thickness of the fl oor
structure and divide this total vertical distance
by the riser height. This gives the number of
risers in the opening.
When counting down from the top to the
tread from which the headroom is measured,
there is the same number of treads as risers.
Therefore, to fi nd the total length of the rough
opening, multiply the tread width by the number
of risers previously determined. Some carpen-
ters prefer to make a scaled drawing (eleva-
tion) of the stairs and fl oor section to check the
calculations.
Total rise
floor to floor
H
Number
of
risers
Height
of
riser
R
Number
of
treads
Width
of run
T
Total
run
L
Well
opening
U
Length
of
carriage
Use stock
tread width
Dimension
of nosing
projection
Well Openings Based on Minimum Head Height of 6'-8"
Dimensions Based on 2 x 10 Floor Joist
8'-0"
8'-4"
8'-6"
8'-9"
8'-11"
9'-1"
12
14
13
14
13
14
14
15
14
14
14
14
14
11
13
12
13
12
13
13
14
13
13
13
13
13
8"
6 7/8"
9 1/2"
10 5/8"
8'-8 1/2"
11'-6 1/8"
9'-5"
10'-1"
9'-5"
9'-0"
10'-2"
9'-5"
10'-8"
9'-2"
10'-8"
10'-0"
11'-1"
9'-1"
10'-10"
12'-10 3/4"
13'-6 1/2"
13'-5 3/4"
14'-7 3/4"
13'-1 1/4"
12'-10"
13'-10 1/4"
12'-5 1/4"
13'-7"
12'-5 1/2"
13'-7 5/8"
11'-4 5/8"
13'-8 1/2"
10 1/2"
11 1/2"
1"
7/8"
1 1/4"
1 1/2"
1 1/8"
1 7/16"
1 1/4"
7/8"
1 5/16"
11/16"
1 1/8"
10 1/2"
11 1/2"
10 1/2"
11 1/2"
10 1/2"
11 1/2"
10 1/2"
11 1/2"
10 1/2"
10 1/2"
11 1/2"
10'-6"
11'-11 1/2"
10'-1 7/8"
9'-9 7/8"
11'-1 1/4"
10'-0 1/4"
10'-10"
9'-7 1/2"
11'-0 1/2"
9'-9 3/4"
11'-2 7/8"
9 13/16"
10 3/8"
9 11/16"
10 1/4"
9 3/8"
9 1/16"
10 1/4"
9 1/4"
10"
9 5/8"
10 3/16"
7 13/16"
7 1/4"
7 11/16"
7 1/8"
7 7/8"
7 5/16"
7 1/2"
7 1/2"
7 5/8"
7 5/8"
7 5/8"
13/16"
1 1/4"
Figure 18-13. A table can be used to determine the number of risers and treads and their dimensions.
(C-E Morgan)