IRC 2018 Stair Building Code Reference
Complete reference for residential stair building code requirements per the International Residential Code (IRC) 2018. Always check with your local building department — local amendments may apply.
Riser Height
- •Maximum: 7-3/4 inches (196mm)
- •Minimum: 4 inches
- •Ideal range: 7" to 7-1/2" for comfort
- •Maximum variation between any two risers: 3/8 inch
- •Open risers: max 4" opening (for child safety)
Tread Depth
- •Minimum: 10 inches (254mm) nosing to nosing
- •Minimum: 11 inches if measuring tread board depth (with 1" nosing overhang)
- •Maximum variation between any two treads: 3/8 inch
- •Nosing overhang: 3/4" to 1-1/4" projection beyond the riser
Stair Width
- •Minimum: 36 inches clear width
- •Measured between finished walls or between wall and guard
- •Handrails may project up to 4.5" into the required width on each side
- •Minimum width at and below handrail: 31.5" (with handrails on both sides)
Headroom
- •Minimum: 6 feet 8 inches (80 inches / 2032mm)
- •Measured vertically from the nosing line to the ceiling above
- •Must be maintained for the full length of the stairway
Handrails
- •Required when there are 4 or more risers
- •Height: 34 to 38 inches above the stair nosing
- •Must be continuous for the full length of the stairs
- •Must extend horizontally at least 12" beyond the top riser
- •Must extend at the slope of the stair for one tread depth beyond the bottom riser
- •Graspable profile: 1-1/4" to 2" diameter (circular) or perimeter 4" to 6-1/4"
Guardrails
- •Required on open sides of stairs more than 30" above grade
- •Minimum height: 36 inches (residential)
- •Baluster spacing: 4" sphere rule (no opening larger than 4")
- •Must resist 200 lbs of force applied in any direction at the top rail
Landings
- •Required at top and bottom of every stairway
- •Required where stairs change direction
- •Depth must be at least equal to the stair width (min 36")
- •Width must be at least as wide as the stair
- •Maximum vertical rise between landings: 12 feet (147 inches)
Spiral Stairs (Special Provisions)
- •Minimum clear width: 26 inches
- •Minimum tread depth at 12" walk line: 7-1/2 inches
- •Maximum riser height: 9-1/2 inches
- •Minimum headroom: 6 feet 6 inches
- •Must have a handrail on the outer wall
Note: These are IRC 2018 requirements. Your local jurisdiction may have adopted a different edition or added amendments. Always verify with your local building department before construction.