1. Competency: 305.00 Design and Draw Stair Systems
Objective:
Explain the calculations for rise, run, total rise, total run, and floor cutout.

2. 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”

3. 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

4. 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”

5. 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”

6. Stair Calculation Total rise Example: 8’-0”
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”

7. Stair Calculation Number of risers Example:
Convert TOTAL RISE to inches
Divide TOTAL RISE by 7
Example:
TOTAL RISE =
106.25”
/ 7 =
15.17
Number of risers =
15 or 16

8. Stair Calculation Height of riser Example: TOTAL RISE inches 106.25”
Divide by number of risers
Each riser must be equal in height
Example:
106.25”
/ 15
TOTAL RISE = 7.08”

9. Stair Calculation Ensure accuracy of riser and tread dimensions
One less tread than risers

10. Stair Calculation Total Run Example
Tread width multiplied by number of treads
Example
Tread width = 10”
Number of treads = 14
TOTAL RUN = 140”

11. 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