Ship stair design

What is the correct angle for ship stairs?

Last Updated on: September 5, 20268 min read

For workplaces covered by federal OSHA’s general-industry rules, ship stairs must be installed at a slope of 50 to 70 degrees from horizontal. Choosing an angle within that range also requires attention to feasibility, tread geometry, headroom, rails, loads and the complete installation.

How federal OSHA classifies access systems by angle under 29 CFR 1910.25 and Figure D-10

Access system	Angle from horizontal	Important qualification
Ramp	30 degrees or less	Other ramp and walking-surface requirements may apply
Standard stair	30–50 degrees	The required rise, tread depth and width also apply
Ship stair	50–70 degrees	Permitted only when standard stairs are not feasible
Alternating tread-type stair	50–70 degrees	Uses alternating treads and has separate dimensional criteria
Ladder	60–90 degrees	A ladder is a different access system governed by different provisions

What is the correct ship-stair angle?

The correct regulatory range for a ship stair in a workplace covered by federal OSHA’s general-industry rules is 50 to 70 degrees from horizontal. OSHA states this range in 29 CFR 1910.25(e)(1). The agency also defines a ship stair—sometimes called a ship ladder—as a stairway equipped with treads, stair rails and open risers that has a slope between 50 and 70 degrees from horizontal. An angle inside this range is necessary, but it does not by itself make an installation compliant. OSHA allows ship stairs only when the employer can demonstrate that standard stairs are not feasible. The stair must also satisfy requirements for rise, tread depth, width, uniformity, clearance, landings, structural capacity, handrails and fall protection. The correct angle is therefore an output of a complete access decision: it must fit the physical space, remain within the 50-to-70-degree range and work with every other requirement that governs the installed system.

Why ship-stair angle matters

Angle governs the basic tradeoff in a compact stair. As the angle becomes steeper, the horizontal run needed to reach a given elevation becomes shorter. That reduced footprint is the principal reason to consider a ship stair. But a steeper climb also changes tread engagement, body position and the experience of ascending or descending. At a given vertical rise between treads, increasing the angle reduces the horizontal run between successive tread nosings. Designers cannot treat angle, rise and tread arrangement as independent selections. OSHA’s minimum tread depth for ship stairs is 4 inches, while the vertical rise between tread surfaces must be 6.5 to 12 inches. Those are regulatory limits, not a statement that every combination inside the limits is equally appropriate for every workforce or task. A sound design considers frequency of access, expected footwear, whether users carry tools, exposure to oil or weather, emergency planning and the way a user approaches each landing. The objective is not to choose the steepest angle that fits. It is to use the least constrained configuration that safely and lawfully solves the access problem.

Where ship stairs sit between stairs and ladders

OSHA’s angle ranges help distinguish access systems, but the ranges overlap at their boundaries. Standard stairs are installed at 30 to 50 degrees from horizontal. Ship stairs and alternating tread-type stairs are installed at 50 to 70 degrees. Figure D-10 depicts ladders from 60 to 90 degrees. This does not mean that angle alone converts one system into another. A ship stair has full-width treads, open risers and stair rails. An alternating tread-type stair has staggered treads designed so users normally step on alternating levels. A fixed ladder uses rungs, steps or cleats and is separately defined in §1910.21. The distinction matters between 60 and 70 degrees, where the illustrated angle bands for ship stairs and ladders overlap: the system’s construction and intended use determine its classification and applicable requirements. At 50 degrees, a project team should likewise not select whichever category offers the preferred dimensions. Standard stairs are the required choice for regular and routine travel, and ship stairs are available only after the employer can demonstrate that standard stairs are infeasible.

How angle changes footprint and tread geometry

A stair angle is measured between the stair’s line of travel and a level horizontal reference. In simplified geometry, horizontal run equals vertical rise divided by the tangent of the angle. For the same floor-to-floor height, a 50-degree layout requires substantially more horizontal run than a 70-degree layout. That relationship is useful during early planning, but an installed stair is not defined by one triangle alone. The number of risers, actual rise between tread surfaces, tread spacing, top transition, nosing geometry and landing conditions must be resolved together. Tread depth is also not necessarily identical to the horizontal run between adjacent nosings when treads overlap. OSHA’s 2025 interpretation for standard stairs explains that required tread depth is measured horizontally between vertical planes at the foremost projections of adjacent treads, excluding steeply beveled or rounded portions. That interpretation addresses §1910.25(c), not the ship-stair rule in paragraph (e), so it should not be presented as a new ship-stair formula. It does illustrate why drawings should define exactly what each dimension represents instead of relying on informal terms such as step size.

How to measure a ship-stair angle

Measure the angle from a true horizontal reference to the stair’s pitch line, not from a wall, handrail or individual tread surface. A digital inclinometer placed on a straight reference aligned with the pitch can support a field check, while coordinated shop drawings should establish the intended angle before fabrication. Field measurements also need context. Floors and platforms can be out of level; finishes can change the finished elevation; supports can shift during installation; and a reading taken from a rail may not represent the stair pitch. Confirm the finished floor-to-floor rise and the available horizontal run, then compare the calculated pitch with the fabricated and installed condition. Record the method, instrument and location of the measurement when compliance documentation matters. Angle verification should occur alongside checks of the 6.5-to-12-inch vertical rise, minimum 4-inch tread depth, minimum 18-inch tread width, tread and riser uniformity, and required vertical clearance. A compliant nominal angle cannot cure a nonuniform flight or an obstruction that reduces headroom below the required 6 feet 8 inches.

When OSHA permits a 50-to-70-degree ship stair

A constrained footprint is relevant, but OSHA requires more than a preference for compactness. Section 1910.25(b)(7) requires standard stairs where operations necessitate regular and routine travel between levels, including access to operating platforms for equipment. Section 1910.25(b)(8) says ship, spiral or alternating tread-type stairs may be used only when the employer can demonstrate that standard stairs are not feasible. The standard does not reduce this to a single clearance number. A practical feasibility record can identify the elevation change, available plan area, structural boundaries, equipment and process conflicts, required access route, and layouts considered. Cost or convenience alone should not be treated as proof of physical infeasibility. When ship stairs are permitted, §1910.25(b)(9) requires them to be installed, used and maintained according to the manufacturer’s instructions. The selected angle should be documented in the context of that decision. This creates a clearer compliance record than beginning with a 70-degree product and working backward to justify it after the access arrangement has already been chosen.

What angle cannot tell you about compliance

Angle is only one element of OSHA compliance. Under §1910.25(b), covered stairs must have uniform riser heights and tread depths between landings, adequate vertical clearance, landings of prescribed width and depth, and the capacity to support at least five times the normal anticipated live load—never less than a 1,000-pound concentrated load applied at any point. Section 1910.28(b)(11)(iii) requires handrails on both sides of every ship stair and alternating tread-type stair. Landings four feet or more above a lower level may require guardrail or stair rail protection at exposed sides and edges. Section 1910.29 establishes detailed criteria for those systems, including height, openings, clearance, graspability, surface condition and strength. Connections, supporting structures and adjacent openings must also be considered. A stair at 60 degrees can still be noncompliant because its tread depth is insufficient, its rise varies, its rails do not meet the applicable criteria or standard stairs were feasible. Compliance belongs to the complete workplace condition—not to the angle printed on a product description.

How to choose an angle for the application

Begin with the required access and the assumption that standard stairs are used where feasible. If a documented constraint supports ship stairs, establish the finished rise, clear run, required width, landing space and overhead envelope. Then model candidate angles inside OSHA’s 50-to-70-degree range. A shallower candidate consumes more floor area but generally provides greater horizontal progression per step; a steeper candidate conserves space but demands closer review of user movement and operating conditions. Evaluate the design with the people who understand the work: the employer’s safety representative, facility owner, qualified designer or engineer, fabricator and installer. Consider expected travel frequency, tools or materials carried, drainage, slip resistance, corrosion, lighting, access control and rescue or emergency procedures. Confirm that doors and gates do not reduce the effective landing depth below the permitted condition. Finally, check federal OSHA applicability. Construction, maritime and other work may involve different standards, and OSHA-approved State Plans can have requirements that differ from federal administration. Building, fire and accessibility codes and the authority having jurisdiction may impose additional constraints.

Configure the angle before requesting a quote

The Ship Stair Builder helps teams explore how angle changes a custom stair configuration. Enter the floor-to-floor height, available dimensions and a target angle to view the resulting concept geometry and test alternatives within the builder’s selected dimensional checks. The tool can flag an angle outside OSHA’s 50-to-70-degree ship-stair range and help identify related dimensional inputs that need correction or review before a quotation moves forward. Early checks can reduce avoidable specification errors, redesign and conditions that may contribute to OSHA citations or penalties. The builder does not certify a stair, guarantee OSHA compliance or eliminate the risk of a fine. It cannot demonstrate that standard stairs are infeasible, assess how employees will use the stair, verify structural capacity, design all fall-protection components, validate installation or resolve state and local requirements. Use the configuration as a planning and quotation aid. A qualified party should review the complete application, engineering, rails, landings, connections, surrounding walking-working surfaces and jurisdictional requirements before fabrication and use.

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Sources

This article summarizes selected federal requirements and is not a site-specific compliance determination, engineering approval or legal opinion.