Most buildings of architectural heritage in Paris and its surroundings are built with Lutetian limestone. Several historic buildings of the ‘Vexin Normand’ region show Lutetian limestone in the upper parts of their walls, while the lower parts are built with a chalk known as ‘Pierre de Vernon’. The ‘Pierre de Vernon’ appears up to the first metre, although in exceptional cases it can reach the middle height of a building. Commonly, chalks exhibit low durability due to their high porosity. However, ‘Pierre de Vernon’ is supposed to have greater durability than other chalks because of its historic use for basement construction. The objective of this research was to understand the use of the ‘Pierre de Vernon’ in the lower part of the constructions. A petrophysical characterization of Vernon chalk and Lutetian limestone was carried out, focusing mainly on the differences in porosity and water uptake. Salt crystallization tests were done to contrast their response to decay. Colour and roughness measurements and scanning electron microscope observations were performed. Results show that the different porous networks of these two limestones lead to a high contrast in their hydric properties and responses to decay, and the use of Vernon chalk in the lower sections of buildings has been found to be appropriate.