Competency: 305.00
Design and Draw Stair
Systems
Objective: 305.03
Explain the calculations for rise, run, total
rise, total run, and floor cutout.
Building Considerations
 Minimum headroom = 6’-8”
 Riser height = 7” to 7-5/8”
 Riser material thickness = ¾”
 Tread depth = 10” to 11-1/2”
 Tread material thickness = 1-1/4”
 Tread width = 36” clear above/below
handrail
 Handrail height = 30” to 38”
Building Considerations
 Guardrail heights
 Required
if landing is 30” above floor or
grade
 Minimum height = 36”
 Vertical members spacing maximum = 4”
 Do not allow passage of 6” diameter
sphere
Building Considerations
 Require handrail for 4 or more risers
 Minimum 1-1/2” between handrail and
wall
 Handgrip does not exceed 2-5/8” in
cross-section
 Local codes for winders, spiral stairs,
illumination, etc
 Nosing projects 1-1/8” to 1-1/2”
General Design Rules
 Slope (rise-to-run) ratio between 300
and 350
 Sum or two risers & one tread equals
approximately 25”
 Riser height multiplied by tread width
equals approximately 75”
 Sum of one riser & one tread equals 17”
to 18”
Stair Calculation
 Total rise





Distance: finished
lower floor to finished
Thickness of ceiling
material
Width of floor joist
Thickness of subfloor
Thickness of finished
floor
 Example:
8’-0”
(gypsum board or drywall) 1/2”
(2”x 8” joist)
7-1/4”
(1/2” plywood sheathing) 1/2”
(floor & underlayment)
1”
Total Rise =
8’-10 ¼”
Stair Calculation
 Number of risers
 Example:

Convert TOTAL
RISE to inches

TOTAL RISE =
106.25”

Divide TOTAL
RISE by 7

106.25 / 7 =
15.17

Number of risers =
15 or 16
Stair Calculation
 Height of riser

 Example:
106.25”
TOTAL RISE
inches
/ 15


Divide by number
of risers
Each riser must be
equal in height

TOTAL RISE =
7.08”
Stair Calculation
 Ensure accuracy of riser and tread
dimensions
 One less tread than risers
Stair Calculation
 Total Run

Tread width
multiplied by
number of treads
 Example
10”

Tread width =

Number of treads =
14

TOTAL RUN = 140”
Stair Calculation
 Floor cutout size (upper level)
Lay out scaled drawing and calculated
rise/run information
 Draw a line, along stair nosing, from
bottom tread to top tread
 Measure vertical line representing
headroom
 Draw a parallel line from bottom tread to
top tread
 Measure resulting stairwell rough opening
