Ship’s ladder code requirements sit at the intersection of two rulebooks: the International Building Code, which sharply limits where a ship’s ladder can serve as a means of egress, and OSHA’s general industry standard at 29 CFR 1910.25, which treats ship stairs as a recognized stairway type in workplaces and sets dimensional and structural specifications for them. If you are designing, installing, or inspecting one, you need to check both, because the standard that applies depends on the building’s use, and the requirements are not identical.
Where a Ship’s Ladder Is Allowed
The IBC does not allow ship’s ladders as a general substitute for stairs. Under Section 1011.15, they are permitted as a means of egress only in Group I-3 occupancies (detention and correctional facilities) for access to control rooms or elevated observation stations that do not exceed 250 square feet and serve no more than three occupants. They are also allowed for access to unoccupiable roofs.1International Code Council. IBC Chapter 10 – Section 1011.15 Ship’s Ladders The three-occupant cap is strict; some secondary sources cite a ten-occupant figure, which is wrong.
OSHA covers a broader set of situations. Under 29 CFR 1910.25(e), ship stairs are permitted in general industry workplaces subject to the dimensional and structural rules in that section.2Occupational Safety and Health Administration. 29 CFR 1910.25 – Stairways In practice that opens the door to access to mechanical platforms, mezzanines, and equipment areas where a conventional stairway will not fit, provided no overriding IBC restriction applies.
Local jurisdictions amend the IBC frequently, so the permitted uses in your area may be broader or narrower than the model code. Check the locally adopted version before assuming the baseline IBC governs.
The 50 to 70 Degree Angle
Both the IBC and OSHA define a ship’s ladder by its pitch: between 50 and 70 degrees from horizontal.2Occupational Safety and Health Administration. 29 CFR 1910.25 – Stairways Anything shallower has to meet standard stairway rules. Anything steeper is treated as a fixed ladder under a separate set of requirements. A few degrees off the pitch during installation can reclassify the entire structure at inspection.
Tread and Riser Dimensions
The IBC and OSHA specify tread and riser dimensions differently, and if both apply to the installation you meet the stricter of the two.
- IBC tread depth: minimum 5 inches, with tread depth plus nosing projection totaling at least 8½ inches.3International Code Council. IBC Chapter 10 – Section 1011.15.2 Treads of Ship’s Ladders
- OSHA tread depth: minimum 4 inches, with no separate nosing projection requirement.2Occupational Safety and Health Administration. 29 CFR 1910.25 – Stairways
- IBC riser height: maximum 9½ inches.
- OSHA riser height: open risers with a vertical rise between 6½ and 12 inches between tread surfaces.
The IBC’s nosing rule catches people out. A bare 5-inch tread does not pass on its own; the nosing has to project far enough that the combined figure reaches 8½ inches, which gives the foot a usable landing surface on a stair much shallower than a normal one.
Handrails on Both Sides
The IBC requires handrails on both sides of a ship’s ladder, with no exception for short runs or low mounting heights.4International Code Council. IBC Chapter 10 – Section 1011.15.1 Handrails of Ship’s Ladders Users should maintain three points of contact throughout the climb.
The IBC’s ship’s ladder provisions do not set a separate handrail height, so the general handrail rules in Section 1014 apply. OSHA-regulated workplaces look to 29 CFR 1910.28 for handrail and guardrail obligations, which addresses fall protection broadly rather than fixing a ship-stair-specific height.5Occupational Safety and Health Administration. 29 CFR 1910.28 – Duty to Have Fall Protection and Falling Object Protection Handrail heights between 30 and 37 inches, measured vertically from the tread nosing, generally satisfy the applicable standards. Rails need enough clearance from any adjacent wall to allow a full hand wrap, and they should run continuously without interruption.
Width, Load Capacity, and Landings
The IBC sets minimum clear width at and below the handrails at 20 inches.1International Code Council. IBC Chapter 10 – Section 1011.15 Ship’s Ladders OSHA sets a minimum tread width of 18 inches.2Occupational Safety and Health Administration. 29 CFR 1910.25 – Stairways Where both apply, the 20-inch IBC number controls. These widths assume one person at a time; ship’s ladders are not built for two-way traffic.
OSHA requires every stairway, including ship stairs, to support at least five times the anticipated live load, with a minimum concentrated load of 1,000 pounds at any point.2Occupational Safety and Health Administration. 29 CFR 1910.25 – Stairways Prefabricated units rated at only 250 or 300 pounds do not meet that requirement for workplace use.
Landings at the top and bottom have to be level and clear. The upper platform should be at least as wide as the ladder so a person is not stepping off into open space during the transition. Anchoring at the floor and upper structure must be secure enough that the structure does not shift or deflect noticeably in use.
Anchoring and Fastening
Federal specifications for metal ladders call for attachment to concrete or masonry using expansion bolts of at least ½-inch diameter, with clip angles riveted or bolted to the stringers and spaced no more than 48 inches apart along the ladder. Attachments to structural steel are welded or bolted. Misaligned bolt holes are treated as a rejection defect during inspection because the 1,000-pound concentrated load transfers through those connections and a sloppy hole invites fatigue and loosening.
Fall Protection at the Top
Where a ship’s ladder passes through a floor opening on the upper level, the opening itself becomes a fall hazard. OSHA requires guardrails with toeboards on all exposed sides of the hole except the entry point, and at the entry either a self-closing gate or an offset that keeps a worker from walking straight into the opening.5Occupational Safety and Health Administration. 29 CFR 1910.28 – Duty to Have Fall Protection and Falling Object Protection Self-closing gates are the common choice because they cannot be left open by accident. Missing top-of-ladder protection is one of the more common citations OSHA writes on otherwise compliant installations.
ADA Accessibility Boundary
A ship’s ladder cannot serve as part of an accessible route. The 2010 ADA Standards for Accessible Design limit accessible routes to walking surfaces no steeper than 1:20, doorways, ramps, elevators, and platform lifts.6ADA.gov. 2010 ADA Standards for Accessible Design A structure pitched between 50 and 70 degrees does not qualify. The corollary is that a space reachable only by a ladder, catwalk, crawl space, or very narrow passageway is exempt from ADA accessibility requirements entirely. So a mechanical room or roof served only by a ship’s ladder is fine; a space that any occupant needs accessible access to must have a compliant path in addition to the ladder.
Ship’s Ladder or Alternating Tread Device?
Alternating tread devices solve a similar tight-space access problem but are treated separately under IBC Section 1011.14. They can serve mezzanines up to 250 square feet with up to five occupants, which is a broader allowance than the base IBC gives ship’s ladders. Their dimensions differ too: a minimum 5-inch tread depth with a projected depth of at least 10½ inches, and a maximum 8-inch rise per step. For access to a small mezzanine, the alternating tread device is often the code-compliant option where the ship’s ladder is not.
Penalties for Getting It Wrong
OSHA violations related to ship stairs fall under the standard penalty structure. Effective January 15, 2025, OSHA can assess up to $16,550 per serious violation and up to $165,514 per willful or repeated violation, with failure-to-abate penalties of $16,550 per day past the abatement deadline.7Occupational Safety and Health Administration. OSHA Penalties These figures adjust annually for inflation. The most common citations involve missing or non-compliant handrails, pitches outside the 50-to-70-degree range, tread dimensions below the minimum, and missing fall protection at the top. Building code violations are handled separately through local permitting and inspection, and a failed inspection means the structure cannot be used until it is corrected.