Acceptable CO₂ levels in offices

Below 800 ppm: excellent. Below 1000 ppm: meets BS EN 16798-1 Category II — the standard UK office target. 1000–1500 ppm: acceptable transient, action if sustained. Above 1500 ppm: ventilation failure, measurable productivity impact, occupant complaints likely.

BS EN 16798-1 derives the 1000 ppm threshold from the 10 L/s per person outdoor air rate at typical CO₂ generation. The Harvard COGfx studies tested 600, 945 and 1400 ppm with measurable cognitive differences across the range.

Measure at breathing-zone height in every meeting room and in a representative grid across open-plan workspace. Use the steady-state value, not the instantaneous peak. Compare against occupancy data.