Ammonia (NH3), methane (CH4), nitrous oxide (N2O) and particulate matter (PM2.5 and PM10) emissions were monitored in two different buildings for laying hens in Italy, both housing approximately 60,000 hens each. The first unit had an in-house prolonged droppings storage (deep-pit), the ground floor was for manure storage and the hens were housed on the first floor. The second unit had a manure removal system for lower environmental impact, where the droppings are dried on ventilated belts. The data were collected continuously in six periods of approximately 1 week each, over one whole year, using a photoacoustic detector (Bruel&Kjaer) to measure NH3, CH4 and N2O and an on-line instrument to measure PM. The ventilation rate was also continuously recorded in order to determine emissions. NH3 emission factors were 0.163 kg yr−1 hen place−1 for the deep-pit system and 0.062 kg yr−1hen place−1 for the ventilated belt. The ventilated belt emission factor is significantly higher than that given for the corresponding technique reported in the IPPC ILF BREF (0.035 kg yr−1 hen−1 place−1), based on Dutch studies. The emission factor for the deep-pit house is fully compatible with the value assessed by Italy in the IPPC-TWG, 2002 (0.154 kg yr−1 hen−1 place−1), but much lower than the Dutch value (0.386 kg yr−1 hen−1 place−1) for the same technique. This result confirms that the technique can reduce NH3 emissions in countries with warmer climates, where higher temperatures and ventilation rates lead to faster and improved drying of the manure in the pit. The NH3 emission reduction factor for the ventilated belt technique, compared to the deep-pit technique, was 61%.The CH4 emission factors measured in our work were 0.08 kg yr−1 hen place−1 for the ventilated belt technique and 0.03 kg yr−1 hen place−1 for the deep-pit technique. No significant emissions were registered for N2O, which was consistently close to zero for both techniques. PM emissions were greater from the deep-pit system in comparison with the ventilated belt system.