Habitable rooms: openable area ≥ 4% of floor area (or mechanical 0.35 ACH whole-house)
2025 RCNYS §R325.1.2 Natural ventilationDescription
Habitable rooms must have an aggregate openable area to the outdoors equal to at least 4% of the floor area — through windows, skylights, doors, or louvers. Openings must be readily accessible / controllable by occupants. Alternative: a whole-house mechanical ventilation system capable of 0.35 air changes per hour per M1505, OR a kitchen local-exhaust system per M1505. Adjoining sunrooms / porches count for ventilation under specific conditions.
Why this exists
4% openable area is roughly half the 8% glazed-area requirement — a typical double-hung window meets both at once. Mechanical alternatives matter in tight envelopes (modern high-R homes can't rely on infiltration). Architects designing to current energy code should plan whole-house mechanical ventilation from day one.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
openableShare | min | 4 | % of floor area | Openable area as share of room area |
wholeHouseACH | min | 0.35 | ACH | Mechanical whole-house ventilation rate (M1505 alternative) |
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
- Garage / dwelling fire separation · IRC R302.6
- Natural light in habitable rooms · IRC R303.1
- Habitable space minimum ceiling height · IRC R305.1
- Egress window net opening dimensions · IRC R310.2
- Stair riser, tread, and headroom · IRC R311.7
Last reviewed 2026-05-15.