A ship ladder is another type of stair system that the code provides guidance on. However when provided it is very clear that the code does not allow ship ladders to be used in-lieu of conventional stairs as a means of egress.
When ship ladders are installed within an individual dwelling unit, the International Residential Code (IRC) provides some guidelines as to the width, riser, tread, and handrail requirements.
Although this type of stair system might be difficult to use, it is only allowed where the space it serves is provided with an egress compliant stairway or ramp, or if the space it serves does not require a means of egress.
It is important to note that there is an exception in the code that does allow a ship ladder to be used as a means of egress only if the space it serves is a loft, mezzanine, or similar area that is 200 gross square feet or less.
However the space must not provide exclusive access to a kitchen or bathroom. Meaning that if the loft, mezzanine, or space contains or provides the only access to a kitchen or bathroom, it cannot be used as a means of egress and another egress compliant stair must be provided.
This exception was added to address small lofts or mezzanines within a tiny house where this would be convenient.
Therefore to understand if a ship ladder meets the size and clearance requirements of the 2018 International Residential Code (IRC), we need to look at Section R311.7.12.
Ship Ladder Width
What is the required width of a ship ladder?
The clear width at and below the handrails shall be not less than 20 inches.
Ship ladders must be at least 20 inches in width where measured at and below the handrails.
Riser Height for Ship Ladder
What is the maximum height of a ship ladder riser?
The riser height shall be not more than 9-1/2 inches.
Tread Depth for Ship Ladder
What is the minimum depth of a ship ladder tread?
Treads shall have a depth of not less than 5 inches. The tread shall be projected such that the total of the tread depth plus the noising projection is not less than 8-1/2 inches.
Handrail Height for Ship Ladder
What is the required handrail height for a ship ladder?
Handrails shall be provided on both sides of ship ladders and shall comply with Section R311.7.8.2 to R311.7.8.6. Handrail height shall be uniform, not less than 30 inches and not more than 34 inches.
For adequate safety to be provided for the user, unlike conventional stairs that only requires a handrail at one side, ship ladders require handrails at both sides due to its steepness.
As for the handrail projection, clearance, and grip size, this section refers you to the conventional staircase handrail standards found in Section R311.7.8.2 through R311.7.8.6. To graphically see what this looks like be sure to check out this POST.
When it comes to the height, it differs from conventional stair handrails. The top of the handrail must be located not less than 30 inches and not more than 34 inches when measured vertically above the imaginary line connecting the leading edge of the treads.
To best illustrate this, see the image above.
So this basically sums up the basic code requirements for ship ladders within residential dwelling units that are subject to the International Residential Code (IRC).
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* Reference Source – 2018 International Residential Code – [Buy on Amazon]
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