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**Competency: 305.00 Design and Draw Stair Systems**

Objective: Explain the calculations for rise, run, total rise, total run, and floor cutout.

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**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”

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**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

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**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”

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**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”

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**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”

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**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

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**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”

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**Stair Calculation Ensure accuracy of riser and tread dimensions**

One less tread than risers

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**Stair Calculation Total Run Example**

Tread width multiplied by number of treads Example Tread width = 10” Number of treads = 14 TOTAL RUN = 140”

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**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

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