competency: 305.00 design and draw stair systems objective: 305.03 explain the calculations for...
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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 Convert TOTAL
RISE to inches
Divide TOTAL RISE by 7
Example: TOTAL RISE =
106.25”
106.25 / 7 =
15.17
Number of risers =
15 or 16
Stair Calculation
Height of riser
TOTAL RISE inches
Divide by number of risers
Each riser must be equal in height
Example:
106.25”
/ 15
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 Tread width =
10”
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