Ramp Slope Compliance Under a Property-Line Constraint
A church is installing a temporary accessibility ramp at a side door whose threshold sits 27 inches above the sidewalk. The available horizontal distance from the door to the property line is 26 feet. A 5-foot-square landing is required at the top of the ramp, and nothing may extend past the property line. The code the contractor cites limits ramp slope to 1:12 - one unit of rise for every 12 units of run - and also limits the rise of any single run to 30 inches, with a 5-foot landing required at the top, bottom, and between runs. The contractor proposes a 21-foot run beyond the landing and says, “27 inches over 21 feet is about 1:9.3, close enough.” A volunteer measures the same 27 inches and 21 feet and reports “27 ÷ 21 = 1.29, so the slope is 1.29:1 and far too steep.” The building committee must decide whether the proposal can be approved, and if not, what layout would fit.
1. Convert units and determine the actual slope of the proposed 21-foot run. State whether it complies and how much run would be required at the maximum allowable slope.
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Convert the run to inches so rise and run share a unit: 21 ft × 12 = 252 in.
Slope as a ratio: 27 in rise to 252 in run = 27:252 = 1:9.33. The maximum permitted is 1:12, so the proposal is too steep; it rises 27 inches in the run that should be used for only about 27/12 = 2.25 ... more directly, dividing 252 by 27 gives 9.33, well short of 12.
Required run at 1:12: 27 in × 12 = 324 in = 27 ft.
With the mandatory 5-ft top landing, the project needs 27 + 5 = 32 ft of horizontal distance. Only 26 ft is available, so no single straight run can satisfy both the slope limit and the property line. The proposal fails on slope and cannot be repaired by relabeling it.
2. Diagnose the volunteer's “1.29:1” conclusion. Where exactly did the reasoning break down, and what should the number 1.29 actually be called?
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The volunteer divided 27 inches by 21 feet without converting, producing 1.286 with mixed units. That quotient is 1.29 inches of rise per foot of run - a perfectly usable description of slope, but not a unitless ratio of 1.29:1.
To express rise:run as a ratio comparable to 1:12, both quantities must be in the same unit: 27 in : 252 in, which reduces to 1:9.33. The volunteer's 1.29 in/ft converts to the same thing: 1.29 in per 12 in of run is 1:9.3.
So the volunteer reached the right verdict (too steep) through a unit mismatch, and the contractor reached the right number (about 1:9.3) while drawing the wrong conclusion (“close enough”). The lesson is that a slope ratio only means something when rise and run are expressed in the same unit, and that “close to 1:12” on the steep side is still noncompliant.
3. Propose a compliant layout that fits within the 26-foot horizontal limit, showing that it satisfies the slope, landing, and single-run rise rules.
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Use a switchback with two runs. Total rise is 27 in, so split it into two runs of 13.5 in each - well under the 30-in limit for a single run.
Each run at 1:12 needs 13.5 in × 12 = 162 in = 13.5 ft of run. The layout is: 5-ft top landing at the door, upper run of 13.5 ft, 5-ft intermediate landing, lower run of 13.5 ft returning, and a 5-ft landing at the bottom.
Horizontal extent along the wall: the return leg doubles back, so the footprint length is the top landing (5 ft) plus the depth of the two runs and intermediate landing (about 5 ft) plus one run length (13.5 ft) - roughly 23.5 ft, inside the 26-ft limit. Width must accommodate two run widths plus a landing turn, typically about 10–11 ft, which must be confirmed against the side yard. Each run is 13.5 ft long with 13.5 in of rise, satisfying the 1:12 slope and the 30-in rise cap, and every transition has a 5-ft landing.