The description herein refers to a structural heat- insulation spacing, element (1) used for making a "disposable" heat-insulation formwork (10) used to cast reinforced concrete into a crawl space, made up of at least one supporting body (3) defining, inside itself, at least one through-hollow (5) co-axial to such supporting body (3), such through-hollow (5) being suited to minimize a contact surface on the ground provided by such spacing element (1).