Deck Stair Calculator

Building Code Requirements

The 7-11 Rule

The most comfortable stair relationship follows the "7-11 rule":

• 7-inch rise: Comfortable step height for most people
• 11-inch tread: Adequate foot placement space
• Alternative formula: 2 x Rise + Tread = 24-25 inches
• Example: 2 x 7" + 11" = 25" (ideal relationship)

Stair Layout Process

1. Measure total rise: Vertical distance from ground to deck surface
2. Calculate number of steps: Divide rise by ideal step height (7-7.5")
3. Determine actual rise: Total rise / number of steps
4. Calculate total run: (Number of steps - 1) x tread depth
5. Check the formula: Ensure 2 x rise + tread = 24-25"

Stringer Requirements

Step-by-Step Construction

1. Layout the stringers:
   • Mark rise and run on framing square
   • Use stair gauges for consistent layout
   • Mark all cuts on first stringer
   • Test fit before cutting others
2. Cut the stringers:
   • Use circular saw for straight cuts
   • Finish corners with handsaw
   • Sand all cut edges smooth
   • Test fit against deck and ground
3. Install stringers:
   • Attach to deck with joist hangers
   • Set on concrete pads at bottom
   • Check for level and square
   • Secure with carriage bolts
4. Add treads and risers:
   • Install risers first (if using)
   • Overhang treads 1" to 1.5"
   • Use 2.5" deck screws
   • Pre-drill to prevent splitting

Handrail Requirements

• Required for: Stairs with 4 or more risers
• Height: 34" to 38" measured vertically from tread nosing
• Graspability: 1.25" to 2" in diameter
• Returns: Must return to post or wall at ends
• Continuous: Should run full length of stair
• Clearance: 1.5" minimum from wall or other surface

Common Construction Mistakes

• Inconsistent rise heights: More than 3/8" variation between steps
• Inadequate bearing: Stringers not properly supported at bottom
• Poor attachment: Insufficient connection to deck framing
• Narrow treads: Less than 11" depth (excluding nosing)
• Missing drainage: No slope or gaps for water runoff
• Wrong lumber: Using undersized stringers for span

Foundation and Landing

• Concrete pads: 2" thick minimum, below frost line
• Gravel base: 4" compacted gravel under pads
• Landing size: Minimum 3' x 3' at bottom
• Drainage: Slope away from structure 1/4" per foot
• Level stringers: Use shims if necessary on uneven ground