# Winder Staircase Code Requirements

### Winder staircase code requirements

**Winder stairs are allowed under the IRC.** The main rule is tread depth at the **walkline**. Under **IRC R311.7.5.2.1**, **winder treads** must be at least **10 inches deep at the walkline** and at least **6 inches deep at any point** within the clear stair width.

This is the rule most people mean when they search for **winder staircase code**, **winder stair code**, **winder tread depth**, or **winder stair dimensions**.

### Winder stair code at a glance

| Requirement                         | IRC rule                                                |
| ----------------------------------- | ------------------------------------------------------- |
| Are winder stairs allowed?          | Yes. Winder stairs are permitted on residential stairs. |
| Walkline location                   | **12 in.** from the inside of the turn.                 |
| Minimum tread depth at walkline     | **10 in.**                                              |
| Minimum tread depth at any point    | **6 in.**                                               |
| Maximum tread variation at walkline | **3/8 in.** within one flight.                          |
| Maximum riser height                | **7 3/4 in.**                                           |
| Maximum riser variation             | **3/8 in.** within one flight.                          |

### What is a winder staircase?

A **winder staircase** uses tapered or wedge-shaped treads to turn without a full landing. The IRC defines a **winder tread** as a tread with nonparallel edges.

This layout helps fit a stair into a smaller footprint. It is common in **L-shaped stairs**, **U-shaped stairs**, and some **curved stair** layouts.

### What is the walkline on a winder stair?

The **walkline** is the reference line used to measure **winder tread depth**. Under **IRC R311.7.4**, the walkline is located **12 inches from the inside edge of the turn**, measured from the widest point of the clear stair width.

It must stay concentric with the turn and parallel to the direction of travel. On a **winder staircase**, the walkline matters because tread depth changes across the width of the stair.

### Winder tread depth requirements

Under **IRC R311.7.5.2.1**, a **winder tread** must meet three core rules:

* **minimum 10 inches deep at the walkline**
* **minimum 6 inches deep at any point** within the clear stair width
* **no more than 3/8 inch variation** between the deepest and shallowest winder tread at the walkline within one flight

These are the main **winder stair code requirements** for tread geometry. They work with the standard residential stair rules for **riser height**, **riser consistency**, **handrails**, and **guards**.

### Do winder treads need to match rectangular treads?

Not exactly.

Consistently shaped **winder treads** do not need to match adjacent **rectangular treads** within **3/8 inch**. The uniformity rule applies within the winder group and within the rectangular tread group separately.

That means a flight can include both tread types when each group stays internally consistent and code compliant.

### How to measure a winder stair for code compliance

Use this sequence when checking **winder stair dimensions**:

1. Mark the **walkline** at **12 inches from the inside of the turn**.
2. Measure each **winder tread depth** at that walkline.
3. Confirm each tread is at least **10 inches** at the walkline and at least **6 inches** at the narrowest point.
4. Confirm walkline depth variation stays within **3/8 inch** across the flight.
5. Confirm risers, handrails, and guards also meet the applicable code.

### Frequently asked questions

<details>

<summary>How deep do winder treads need to be?</summary>

Under **IRC R311.7.5.2.1**, **winder treads** must be at least **10 inches deep at the walkline** and at least **6 inches deep at any point** within the clear stair width.

</details>

<details>

<summary>Can winder stairs be code compliant?</summary>

Yes. **Winder stairs** can meet code when the treads satisfy the **walkline depth**, **minimum narrow-point depth**, and **uniformity** rules, and the stair also meets the other required **riser**, **handrail**, and **guard** standards.

</details>

<details>

<summary>What code section covers winder stairs?</summary>

The main residential sections are **IRC 2021 R311.7.4** for the **walkline** and **IRC 2021 R311.7.5.2.1** for **winder tread depth**.

</details>

<details>

<summary>Do winder stairs need a landing?</summary>

Not at the turn itself. A **winder staircase** changes direction with tapered treads instead of a full landing. Landings are still required at stair tops and bottoms where the code requires them.

</details>

### Related pages

* [Tread Depth and Risers](/code-compliance/stair-code/tread-depth-and-risers.md)
* [Open Riser Code Requirements](/code-compliance/stair-code/open-riser-code-requirements.md)
* [When is Handrail Required?](/code-compliance/getting-started/when-is-handrail-required.md)


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