Winder stairs: what it means on an inspection

Use this diagram

Copy this HTML to show the diagram with a credit link<img src="https://raftertie.com/charts/raftertie/winder-stairs.svg" alt="A plan view of a quarter turn in a stair with three wedge-shaped winder treads around an open inside corner and a dashed walkline arc marking where tread depth is measured, with labels for the two minimum depths" width="100%"><p><a href="https://raftertie.com/guides/winder-stairs?utm_source=embed&amp;utm_medium=referral&amp;utm_campaign=figure_embed&amp;utm_content=winder-stairs.svg">Shapes are invented. Tread depth is measured on the walkline, a set distance in from the narrow side. by Rafter Tie</a></p>

How to check a winder

1. Find the walkline. It is a line a set distance in from the side of the stair where the treads are narrower, running along the path a person would walk. Tread depth is measured here.
2. Measure the depth at the walkline. Measure from nosing to nosing along the walkline and compare with the minimum the IRC sets; check the current edition.
3. Measure the narrowest point. A winder also has its own, smaller minimum depth at its narrowest point within the width of the stair. The wedge cannot come to a point.
4. Compare winders in the same flight. The depths at the walkline within one flight should be consistent. The code limits how much the largest and smallest may differ. Check the limit in your edition.
5. Do not forget the rest of the stair. Riser height, headroom, stair width and handrails still apply. The IRC stair check covers the riser and tread limits for straight flights.

Common mix-ups

• Winder versus landing. A landing is a flat platform. A winder is a sloping tread that turns. A turn made with a landing and one made with winders are measured differently.
• Winder versus spiral stair. A spiral stair turns around a center column and has its own relaxed rules. Do not apply winder numbers to it.
• Walkline versus centerline. The walkline is set a fixed distance from the narrow side, not at the middle of the stair. Read that distance in the stair section of your edition.
• Narrow end versus walkline. Both are measured, with different minimums. A tread can pass at the walkline and fail at the narrow end.

Winders on the B1

Stairs are part of public safety and special construction, 17% of the B1. Expect a described winder with two dimensions and a question about which one controls. The stair section is R311.7 in the 2021 IRC and R318.7 in the 2024 edition, so find it by name in your table of contents and confirm the numbers in your own book.

Practice it

Check the general stair limits with the IRC stair check, then read guard versus handrail for the parts of a stair that sit beside the treads. Then run a guard's height and openings through the guard and handrail check. Egress window covers the other half of that area of the book. The IRC terms glossary links the rest of the terms.

Know your stairs? Check the rest of the B1

Take the free 10-question check. It is weighted to the seven B1 areas, scored by area and needs no signup, so you see which area costs you the most points. The Rafter Tie course adds timed practice exams, a lesson for each outline area and a study plan built from your exam date.

Sources

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• B1 Residential Building Inspector Content Outline, International Code Council.
• 2021 IRC contents and 2024 IRC contents, International Code Council. Chapters are named, not quoted; open your own copy for the text.
• 2021 IRC Chapter 3, Building Planning and 2024 IRC Chapter 3, Building Planning, International Code Council free public access. Stair, handrail and guard rules are cited by topic, not quoted.