because the crawl spaces must be ventilated

According to the dictates of organic construction, the deep and systematic excavation of foundations is not a desirable thing as it modifies the permeability of the soil to the natural fumes of certain gases that escape from the subsoil.

One of these is the Radon gas, which is naturally radioactive, which would tend in the absence of not properly ventilated crawl spaces or crawl spaces to concentrate on the ground floor rooms.

The national environmental protection agency has ascertained a sample of 5000 houses accumulations of radon radioactivity almost double the natural level.

To avoid this problem, the rooms must be ventilated often and moreover the vespaio underlying the ground floor floor must be equipped with ventilation grilles to allow the gas to escape and keep the structures dry.