Measures · Window-to-floor ratio
Window-to-floor ratio calculator (RAI) FREE
Work out the minimum window area of a room from its floor area. Below the result you find the formula and the standard.
Indicative pre-sizing. It does not replace a structural calculation signed by a licensed engineer. For seismic zones with agS (design ground acceleration) > 0.15g, long spans or use classes III/IV → talk to a structural engineer.
Pick a calculation from the list to start.
Formula, example and standard
S_window ≥ S_floor / 8 (= 12.5%)
Example with the starting values (Floor area: 16 m²): Minimum window area: 2.00 m². Average daylight factor (FLD) ≥ 2% (for habitable rooms).
- National rule: DM 5/7/1975 art. 5 (Italian health ministry decree) → S_window ≥ 1/8 S_floor.
- Average FLD ≥ 2% for habitable rooms (the stricter lighting criterion).
- Always check the municipal building code (regolamento edilizio).
Source: DM 5/7/1975 art. 5 · local building codes · biblus.acca.it
Indicative pre-sizing: it does not replace a calculation signed by a licensed engineer.
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