Stairway and Exterior-Door Landing Check
The flat part at each end, which the stair-layout and stair-code tiles both skip. IRC R311.7.6 wants a landing at the TOP AND BOTTOM of every flight, at least as WIDE as the flight and, on a straight run, 36 in deep in the direction of travel. IRC R311.3 wants 36 in at an exterior door too, plus the rule that catches people: the floor at a required exit door not more than 1.5 in below the top of the threshold -- a landing set a full step down is a fall, not a step. The trap the tile makes visible is that AREA does not settle it: a 30 x 48 in landing has 10 sq ft against a 9 sq ft minimum and still FAILS, because the 36 in is measured along the path you actually walk, not across the landing. Both minimums are editable; IBC and accessible routes want more.
Formula and source
depth ok when landing depth in the direction of travel >= 36 in; width ok when landing width >= the width of the flight or door served; at a door, threshold ok when the landing is not more than 1.5 in below the top of the threshold; smallest compliant landing = minimum depth x served width.
IRC R311.7.6 (a floor or landing at the top and bottom of each stairway, width perpendicular to the direction of travel not less than the width of the flight served, and on a straight run a depth in the direction of travel not less than 36 in) and IRC R311.3 (landings at exterior doors not less than 36 in measured in the direction of travel, with the floor or landing at the required exit door not more than 1.5 in lower than the top of the threshold).
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