Stairs by floor height · 11 ft 9 in
Stairs for an 11 ft 9 in floor-to-floor height
11 ft 9 in (141″) from floor to floor takes 20 risers of 7 1/16″ and 19 treads 10 5/8″ deep: a pitch of 34°, and two risers and a going make 24 3/4″, an easy stride. A straight flight is 16′ 9 15/16″ long and needs an opening of 10′ 10 5/8″ in the floor above.
How it’s worked out
The fewest risers that keep each at most 18 cm (7″) high, all the same: 11′ 9″ ÷ 20 = 7 1/16″. The going follows the stair builders’ rule that two risers and a going make a stride of about 63 cm (25″). There is one tread fewer than risers: the last riser goes up to the upper floor itself.
If 11 ft 9 in is your ceiling height, the stair is taller: add the floor above it, usually 10–14″.
More or fewer steps
Fewer risers make a shorter, steeper stair; more make a longer, easier one.
| Risers | Each riser | Going | Pitch | Run of a straight flight | How it walks |
|---|---|---|---|---|---|
| 18 | 7 13/16″ | 9 13/16″ | 39° | 13′ 11 5/16″ | over the IRC’s 7¾″ riser |
| 19 | 7 7/16″ | 9 13/16″ | 37° | 14′ 9 3/16″ | treads under the IRC’s 10″ |
| 20 | 7 1/16″ | 10 5/8″ | 34° | 16′ 9 15/16″ | comfortable (drawn here) |
| 21 | 6 11/16″ | 11 7/16″ | 30° | 19′ 3/8″ | comfortable |
The IRC (US homes) allows risers up to 7¾″ and asks for treads of at least 10″, 6′8″ of headroom and a width of 36″; states and towns amend it. Check the code that applies to yours.
This stair in each layout
Each drawn for 11 ft 9 in: the flights 36″ wide, the spiral 5 ft across, the square one in a 6 ft stairwell. The size is over the treads. Pick one for its plan, its sizes and its parts.
Change anything
A different width, a turn the other way, closed risers, a steel frame: open the stair in uCAD and set it in the panel, or tell the AI what the stair has to fit into.
Other heights
Other heights: 11 ft 6 in · 12 ft · all heights
Measured between finished floors. A few centimetres change the riser, not the count, until a riser passes 18 cm.