Deflection limits: floors L/360, ceilings L/240-360, interior walls H/180
2025 RCNYS §R301.7 Allowable deflection of structural members (Table R301.7)Description
Maximum allowable deflection under live (and wind) loads, expressed as a fraction of the span L or height H: Floors L/360. Ceilings with brittle finish (plaster, stucco) L/360; with flexible finish (gypsum board) L/240. Rafters >3:12 with finished ceiling not attached: L/180. Interior walls + partitions H/180. Exterior walls with plaster/stucco H/360 (wind); brittle H/240; flexible H/120. Lintels supporting masonry veneer L/600. Cantilever members: L = 2× the cantilever length.
Why this exists
Deflection limits prevent cracking, bouncing, and visual sag. L/360 on a floor means a 12-ft span may deflect no more than 0.4 in — visible-but-acceptable. Tile + stone finishes generally need stricter limits (L/720 is a common upgrade) because they crack at smaller deflection. Architects specifying stone floors or tile counters should call out the stricter deflection on the structural drawings.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
floors | min | 360 | L/N (denominator) | Floor deflection denominator (L/360) |
ceilingsBrittle | min | 360 | L/N | Ceilings with brittle finish |
ceilingsFlexible | min | 240 | L/N | Ceilings with flexible finish (gypsum) |
interiorWalls | min | 180 | H/N | Interior walls + partitions |
masonryVeneerLintel | min | 600 | L/N | Lintels supporting masonry veneer |
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.