| Primary value | ≥ 50% of window area (≈ 5% of floor area) |
| Applies to | Bedrooms · Living rooms · Kitchens (separate) |
| Exceptions | Mechanically ventilated rooms → ventilation rule waived |
| Measured as | Openable (operable) sash area as a fraction of the total window area, AND as a fraction of the floor area. |
| Source | NBC 2016 — Part 8, Section 1 📚 Cross-referenced |
Cross-ventilation is the primary cooling strategy in non-AC Indian housing. The 50% openable rule ensures windows aren't just decorative — at least half can be opened to let air through.
Most window types meet this naturally — sliding windows have ~50% openable, casement windows have 80–100% openable. Fixed glazing alone fails the rule.