It is guaranteed by the different density existing between the indoor-air (warmer) and the outdoor one (colder) . By means of a ridge-opening and side openings, placed at a lower level, it is possible to get a natural circulation of the air coming in through the windows and going out through the ridge-opening.

Besides the different temperature existing between internal and external air, wind as well contributes to float the air around. Of course, it is important that the shelter’s location and its orientation, as well as the control of its openings, guarantee a synergic exploitation of both climatic factors.

In order to avoid the likely inconveniences related to this type of ventilation, lots of devices have been conceived, when proceeding to the building phase:
the arrangement of deflectors near the openings, in order to reduce the negative effect of the wind, mainly in winter;
the realization of doors and windows (for both windows and the small dome), easily adjustable and mechanized by means of an automatic control unit.

The natural ventilation system shows some drawbacks due to the heavy influence that the external climatic conditions have on the air conditioning; as a consequence, this system is mainly suitable for shelters where the concentration of animals is not so huge and, preferably for adult animals, which are less sensitive to climatic changes. The main advantage of the natural ventilation compared to the artificial one, is related to its reliability and to its limited dependence on the employment of energy.
When it is necessary to guarantee a perfect airtight, it is possible to turn to wasistass-type and false frames windows, with the addition of an artificial ventilation system.