Stair Building Code — Rise, Run, Headroom and Railings (IRC)

Rule	Requirement	IRC
Riser height	max 7 3/4"	R311.7.5.1
Tread depth	min 10" (nosing to nosing)	R311.7.5.2
Variation in a flight	max 3/8" between largest and smallest riser or tread	R311.7.5
Nosing	3/4"–1 1/4" when treads are under 11"	R311.7.5.3
Stair width	min 36" above the handrail	R311.7.1
Headroom	min 6' 8" measured from the nosing line	R311.7.2
Handrail height	34"–38" above the nosings	R311.7.8.1
Handrail required	with 4 or more risers	R311.7.8
Guard (railing)	min 36" where the drop is over 30"	R312.1
Baluster gap	a 4" sphere must not pass; 6" in the stair triangle	R312.1.3
Landing	at top and bottom, at least as deep as the stair is wide, min 36"	R311.7.6
Max rise of a flight	151" (12' 7") between landings	R311.7.3

Rule

Requirement

IRC

Riser height

max 7 3/4"

R311.7.5.1

Tread depth

min 10" (nosing to nosing)

R311.7.5.2

Variation in a flight

max 3/8" between largest and smallest riser or tread

R311.7.5

Nosing

3/4"–1 1/4" when treads are under 11"

R311.7.5.3

Stair width

min 36" above the handrail

R311.7.1

Headroom

min 6' 8" measured from the nosing line

R311.7.2

Handrail height

34"–38" above the nosings

R311.7.8.1

Handrail required

with 4 or more risers

R311.7.8

Guard (railing)

min 36" where the drop is over 30"

R312.1

Baluster gap

a 4" sphere must not pass; 6" in the stair triangle

R312.1.3

Landing

at top and bottom, at least as deep as the stair is wide, min 36"

R311.7.6

Max rise of a flight

151" (12' 7") between landings

R311.7.3

Which code applies

Most US states and towns build houses to the International Residential Code (IRC), often with local amendments. The numbers above are from the IRC; your building department has the final say, so check before you build. Decks and deck stairs follow the same rules.

Designing stairs that pass

Start from the total rise, pick the fewest risers that keep each one at or under 7 3/4", and give each tread at least 10". The stair calculator does this and flags any rule you miss. For the railing, the baluster spacing calculator keeps every gap under 4".

Frequently asked questions

What is the maximum stair riser height?

7 3/4" under the International Residential Code (R311.7.5.1). Commercial stairs under the IBC are stricter: 7" maximum and 11" minimum treads.

What is the minimum tread depth?

10" measured horizontally from nosing to nosing (IRC R311.7.5.2).

How much headroom does a stair need?

6' 8" measured vertically from a sloped line through the tread nosings (IRC R311.7.2).

When is a handrail required?

On any flight with four or more risers, 34" to 38" above the nosings, on at least one side (IRC R311.7.8).