The concept of gross square footage versus net square footage requires special attention. The gross living area of a building is measured from the exterior walls and half of the common walls. This calculation method is uniform across the construction industry. That said, in order for the notary to draw up the deed of sale, a surveyor must come and measure the net area, i.e. the final interior space available between the walls. In other words, it is perfectly normal and expected that there is a discrepancy between the gross and net surface area (i.e. in the certificate of location) since these are two different calculation methods.