# How do you fit a straight flight of stairs?

###### Wiki User

###### September 20, 2007 3:09AM

Very simple to explain, very dificult to get right. Here is my

best shot. The 2006 International Building Code states the

following: R311.5.3 Stair treads and risers.

R311.5.3.1 Riser height.

The maximum riser height shall be 7¾ inches (196 mm). The riser

shall be measured vertically between leading edges of the adjacent

treads. The greatest riser height within any flight of stairs shall

not exceed the smallest by more than 3/8 inch (9.5 mm).

R311.5.3.2 Tread depth.

The minimum tread depth shall be 10 inches (254 mm). The tread

depth shall be measured horizontally between the vertical planes of

the foremost projection of adjacent treads and at a right angle to

the tread's leading edge. The greatest tread depth within any

flight of stairs shall not exceed the smallest by more than 3/8

inch (9.5 mm). Winder treads shall have a minimum tread depth of 10

inches (254 mm) measured as above at a point 12 inches (305 mm)

from the side where the treads are narrower. Winder treads shall

have a minimum tread depth of 6 inches (152 mm) at any point.

Within any flight of stairs, the largest winder tread depth at the

12 inch (305 mm) walk line shall not exceed the smallest by more

than 3/8 inch (9.5 mm). So taken that a flight of stairs is the

measurement of floor to floor, or approximately 9ft use the

following to find the rise and run: Floor to Floor Dimention

divided by number of risers that will give you an answer somewhere

between 4 inches and 7 3/4 inches. Some trial and error is needed

here to get an even number that you can work with. 9ft/15 = 7.2

inches for riser height. Run is equal to the depth of each tread

plus any landings. 15*10 = 150 inches or 12.5ft long. The with is

described in the IRC as follows: R311.5.1 Width.

Stairways shall not be less than 36 inches (914 mm) in clear

width at all points above the permitted handrail height and below

the required headroom height. Handrails shall not project more than

4.5 inches (114 mm) on either side of the stairway and the minimum

clear width of the stairway at and below the handrail height,

including treads and landings, shall not be less than 31.5 inches

(787 mm) where a handrail is installed on one side and 27 inches

(698 mm) where handrails are provided on both sides. Hope this

helps!

Terry