What Is the Ship Ladder Calculator?
Calculate ship ladder and alternating tread stair dimensions for steep-angle access in compact spaces. Ship ladders (also called ship stairs or alternating tread stairs) are allowed by building codes for specific applications where conventional stairs don't fit.
How to Use This Calculator
- Enter the total rise and available floor space.
- Set the tread depth and alternating tread offset.
- Review the steep angle, handrail requirements, and code compliance.
Why Accurate Ship Ladder Calculations Matter
Ship ladders operate at steep angles (50° to 70°) and require different code provisions than standard stairs. The IBC Section 1011.15 permits alternating tread devices for specific uses, typically as access to equipment platforms, mezzanines, or single-occupant spaces.
Common Ship Ladder Mistakes to Avoid
- Installing a ship ladder where code actually requires a full compliant stair, such as a primary means of egress for an occupied room. Alternating tread devices are limited to specific secondary-access uses, not general circulation.