Radon gas is a well-known building´s pollutant which can affect negatively people´s health (WHO, 2009). Radon´s source is the soil underneath buildings. Radon moves from the soil to the buildings by advection through cracks and joints, and diffusion through porous materials. Once radon enters buildings it can accumulate in lower areas due to lack of ventilation. Ventilation is one of the main ways to prevent radon from accumulating in enclosed spaces in the case of moderate radon concentrations up to 600 Bq/m3 (Collignan, 2008).
This paper presents the research that has been conducted in a building with moderate levels of radon, using precisely ventilation to reduce these levels. The building is placed in a granitic area at the North of Madrid (Spain) with a high presence of radon (García-Talavera, 2013). The results show how even little ventilation can lower radon concentration up to acceptable levels.