In Spain, houses are built with so-called cottage foundations as is the case in the Nordic countries.
The difference is that cottage foundations in the Nordic countries have a ventilation function.
In Spain, however, you fill the foundations with construction waste and cover it with cement.
This is meant to work as isolation against earth masses and of course for drainage of water.
After 5-10 years, the warm and cold weather forms so much condensation that it will rise up in the floors and walls which in turn causes a strong odor of mug and mildew.
We open up these foundations and install proper cement valves for venting them.
This form of ventilation is offered to fixed prices.