COUNCIL DIRECTIVE 2007/43/EC of 28 June 2007 laying down minimum rules for the protection of chickens kept for meat production.
-EXTRACT FROM ANNEX II
Requirements for the holdings -- control of environment parameters
3. The owner or keeper shall ensure that each house of a holding is equipped with ventilation and, if necessary, heating and cooling systems designed, constructed and operated in such a way that:
(a) the concentration of ammonia (NH3) does not exceed 20 ppm and the concentration of carbon dioxide (CO2) doesnot exceed 3 000 ppm measured at the level of the chickens heads;
(b) the inside temperature, when the outside temperature measured in the shade exceeds 30 °C, does not exceed this outside temperature by more than 3 °C;
(c) the average relative humidity measured inside the house during 48 hours does not exceed 70 % when the outside temperature is below 10 °C.