Spanish to English Tech/Engineering Construction / Civil Engineering Demolition

This comes in a text about the expansion of a railway line from single track to double track under the "demolition" sub-heading. Apparent volume in English seems to be something to do with pharmacy and drugs so it must be something else. Does anyone know? I'm guessing it just means demolition of the volume of a building as it appears from the outside, including the spaces inside since you can't see inside the building to know how much is structure and how much is open spaces, but I have no idea what this would be called in English if it can't be translated directly.