Device and method for measuring the gas permeability of a porous building material

An arrangement and a method for measuring the gas permeability of a porous building material (12) in a building (10) with a surface (11) provide in each case that a closed cavity (20) in the interior of the building (10) at a distance from the surface ( 11) of the building material (12) is provided. Both in the cavity (20) and in the environment (30) outside of the structure (10) in each case an air pressure sensor (42, 43) are arranged. The data of the two air pressure sensors (42, 43) are sent to an evaluation unit (45). The variable air pressure in the environment (30) draws with a time delay, a corresponding pressure curve in the cavity (20) after, so it comes to a delayed adaptation to the atmospheric external pressure.