STEP 1 - Find a location - often in or near a stair is convenient for building occupants as well as contractors. In a 1-story building an oversized custodial closet might be a good choice.
STEP 2 - 10 Ft. Distance - bear in mind that codes require a safety margin of 10’ from the point at which you emerge onto the roof to the nearest edge of the roof. Less than 10’ requires a permanent guard rail.
STEP 3 - Draw a section - by drawing a section you will have an idea of how much room your ship’s ladder will require. Research this link to see how to design a ship’s ladder.*
STEP 4 - Work out head room - another cross section issue. Draw a line parallel to the nosings of the stair with a 7’ vertical clearance. This determines the minimum length of the roof hatch.
STEP 5 - Size opening - you worked out the length, now the width. This depends on your stair width, but should be at least 12 inches wider. The structural drawings need to show how this opening is framed.
STEP 6 - Detail roof opening - the components of this detail include the structural framing of opening, the roof hatch, flashing to the roofing, and anchorage of the stair. I like to include a ladder extension device made by Bilco, the Ladder-Up. This device telescopes up through the open roof hatch to give you something to hold onto as you enter and exit the roof hatch. (A customized installation is required for a ship's ladder.)
STEP 7 - Locate on floor plan - you will need to tie down the exact location so that the roof opening can be coordinated with roof structure.
STEP 8 - Show on roof plan - positioning the roof hatch on the roof plan helps coordinate everyone’s work, like roof drains, HVAC equipment, roof edge guard rail...
Finally, if your roof has multiple levels, work out how to get to all the levels - more roof hatches, ladders, stairs? After you have designed the first ship’s ladder roof access, each succeeding one will be a breeze. One added step is to remind your client how you are “helping with maintenance” by your thorough attention to design.
* This link to the OSH is intentional. I can’t find any OSHA regulation that applies. The 2012 IBC has this to say:
“1009.14 Ship ladders.
Ship ladders are permitted to be used in Group I-3 as a component of a means of egress to and from control rooms or elevated facility observation stations not more than 250 square feet (23 m2) with not more than three occupants and for access to unoccupied roofs.
Ship ladders shall have a minimum tread depth of 5 inches (127 mm). The tread shall be projected such that the total of the tread depth plus thenosing projection is no less than 81/2 inches (216 mm). The maximum riser height shall be 91/2 inches (241 mm).
Handrails shall be provided on both sides of ship ladders. The minimum clear width at and below the handrails shall be 20 inches (508 mm).”
Check out Other Roof Conditions
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Original post date 2FEB14.