StairGen Pro › U-Shaped Winder Stair Calculator (180° Winders)
Guide & codes
This U-shaped winder stair calculator designs a 180° half turn in wood with the treads of the turn fanned around a newel post instead of a landing. It takes up less floor area than a U-shaped stair with a landing and is common in houses where the stairwell is tight.
Enter the total rise (Y), the run of the upper flight (X), the width (W), the steps in each flight (P and Q) and the winders in the turn (K). The calculator divides the 180° between the winders and outputs each one as a separate part, with its shape and its mark. Not to be confused with a double winder stair, which turns twice by 90° with a straight middle flight in between: that one has its own calculator.
When to choose this stair
Choose the 180° winder stair when the stair has to make a half turn in the least possible space: the 5 winders turn around a newel post and replace the double-width landing. It is the compact stair of many houses and duplexes, and the wooden alternative to a spiral when you would rather have straight flights.
A winding half turn is the hardest on the going: next to the newel the treads almost disappear. That is why a wide stair (W = 1,000 mm or more) and a handrail on the outer side are advisable. If a landing fits, the U-shaped stair with a landing is more comfortable; if even less space is available, look at the spiral.
Calculator parameters
Each dimension carries the letter used in the editor and on the drawings.
- YTotal rise
- default 2,600 mm · 500 to 8,000 mm
- Height from the lower floor to the finished upper floor.
- XTotal run
- default 2,400 mm · 500 to 12,000 mm
- Plan length available for the flight (on turning stairs, the upper flight).
- WStair width
- default 1,000 mm · 500 to 2,500 mm
- Clear width of the flight.
- ZTread thickness
- default 50 mm · 3 to 120 mm
- Thickness of the tread (board or plate).
- FNosing
- default 50 mm · 0 to 100 mm
- How far each tread overhangs the one below.
- PSteps, lower flight
- default 5 · 1 to 25
- Steps before the turn.
- KWinder steps
- default 5 · 3 to 10
- Winder treads in each turn.
- QSteps, upper flight
- default 5 · 2 to 25
- Steps after the turn, up to the top.
- TStringer thickness
- default 50 mm · 20 to 120 mm
- Thickness of the stringer board.
How it's calculated
The total rise Y = 2,600 mm is shared between 15 risers (5 below, 5 winders and 5 above): 173.3 mm per step. On the straight flights the run is 280 mm and the tread depth 330 mm.
The 5 winders share the 180° turn around the central newel; each has a different shape, so they appear separately in the bill of materials and in the DXF. Step formula: 627 mm; pitch: 31.8°; verdict: “Comfortable stair”.
If the pitch falls below 30°, the stair is shallow and makes the climb longer than necessary: shorten X or add steps, as the Summary panel suggests.
Result with the default values
Comfort verdict: Comfortable stair.
Complies with IRC / IBC
| Step formula 2R + G | 627 mm | 600 – 660 mm |
| Tread depth | 330 mm | ≥ 280 mm |
| Pitch | 31.8° | 30° – 40° |
| Riser | 173 mm | ≤ 197 mm |
| Going | 280 mm | ≥ 254 mm |
| Clear width | 1,000 mm | ≥ 914 mm |
| Guarding height | 900 mm | ≥ 864 mm |
Steps
| Risers | 15 pcs |
| Riser height | 173 mm |
| Run (going) | 280 mm |
| Tread depth (run + nosing) | 330 mm |
| Open riser gap | 123 mm |
| Pitch | 31.8° |
| Nosing-to-nosing distance | 329 mm |
Wood
| Tread area | 4.992 m² |
| Winder tread angle | 36.0° |
Building codes
The winder rules are the same as on a quarter turn: at least 10 in (254 mm) of tread at the walkline and 6 in (152 mm) at any point under the IRC, and at least 50 mm at the narrow end under Approved Document K. On a 180° turn the treads next to the newel are the critical ones, so check them on the winder sheets of the drawings.
The calculator checks comfort (2R + G, going and pitch) and the building code of the country you pick in the panel (here, IRC / IBC for a dwelling): only the limits that code sets for riser, going, 2R + G, width, pitch, risers per flight and guarding. It is for guidance only: always confirm the code in force and local rules.
Building codes by country, with sourcesParts with the default values
The DXF (AutoCAD 2007, in millimetres or inches) carries these parts with their shop marks: one dimensioned sheet per part, the general arrangement and the bill of materials with weights.
What's in the DXF- Z1StringerBoard 50 × 2
- Z2Winder stringerBoard 50 × 2
- Z3Winder stringerBoard 50 × 1
- Z4StringerBoard 50 × 2
- E1Treadt=50 × 10
- E2Treadt=50 × 1
- E3Treadt=50 × 1
- E4Treadt=50 × 1
- E5Treadt=50 × 1
- E6Treadt=50 × 1
- P1PostTimber 100×100 × 1
- T1Risert=20 × 10
- B1HandrailRound timber Ø50 × 2
- B2BalusterBatten 35×35 × 10
Frequently asked questions
What is a U-shaped winder stair?
A half-turn stair without a landing: the 180° turn is made with winder treads that share the angle around a newel post. It is also called a half-turn winder stair or a 180-degree winder stair.
How many winders in a 180° turn?
Usually between five and seven. With fewer, the treads are very narrow next to the newel; with more, the stair takes up more space. Change K and watch the tread depth and the verdict.
Are 180° winders comfortable?
They are if the going on the walkline is close to that of the straight flights and the riser height stays constant. The weak spot is the newel side, where the treads are narrow, so people tend to use the middle or the wide side.