The authors used a testing program in order to determine the thermal resistance of terra-cotta walls; built with vertical hollow bricks. These bricks could be standard ones, so cavities were 25 cm high, or they could reach 250 cm (story-height bricks). Different hollow shapes were tested under different boundary conditions on temperature. The authors tried to determine for this class of bricks used in France, the most performing outline, from a thermal point of view, under different boundary conditions.