A large part of the school building stock in Andalusia lacks ventilation facilities, so that
the air renewal of the classrooms is achieved through the building envelope (air infiltration) or the
opening of windows. This research analyses the airtightness of the classrooms in Andalusia and the
evolution of CO2 concentration during school hours through in situ monitoring. Pressurization and
depressurization tests were performed in 42 classrooms and CO2 concentration was measured in
two di erent periods, winter and midseason, to study the impact of the di erent levels of aperture
of windows. About 917 students (11–17 years of age) were surveyed on symptoms and e ects on
their health. The mean n50 values are about 7 h-1, whereas the average CO2 concentration values
are about 1878 ppm, with 42% of the case studies displaying concentrations above 2000 ppm with
windows closed
