Foundation setback from slope: H/3 (max 40 ft) from top, H/2 (max 15 ft) from toe; for slopes > 1:3
2025 RCNYS §R403.1.7 Footings on or adjacent to slopesDescription
On slopes steeper than 1:3 (33%): footings must be set back from the top of an ascending slope by at least H/3 (where H is slope height), capped at 40 ft. Footings near a descending slope must have ≥ H/2 setback (capped at 15 ft) and adequate embedment. The top of any exterior foundation must rise at least 12 in + 2% above the elevation of the street gutter or drainage inlet. Alternate setbacks need building-official approval (often supported by a geotechnical investigation).
Why this exists
Hillside building lots benefit from these setbacks — building too close to the top of a slope creates a failure path where the foundation slides off the hillside; building too close to the toe of an ascending slope risks getting hit by debris. Architects working hillside sites should book a soils investigation early; geotechnical recommendations often supersede this prescriptive guide.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
slopeTrigger | min | 0.333 | vertical / horizontal (1:3) | Slope steepness triggering setback rule |
topSetbackFraction | min | 0.333 | H/3 | Setback from top of slope as fraction of slope height |
topSetbackMax | max | 40 | ft | Maximum required setback from top |
Categories
Applies to
- Jurisdiction: New York State
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Habitable space minimum ceiling height · IRC R305.1
- Wind design · IRC R301.2.1
- Seismic provisions · IRC R301.2.2
- Snow loads · IRC R301.2.3
- Floodplain construction · IRC R301.2.4
Last reviewed 2026-05-15.