In order to achieve consistency in national income calculations, industries are defined according to the Standard Industrial Classification. ‘Construction’ covers the erection, repair and demolition of all types of buildings and civil engineering structures. Specialist subcontracting trades, such as asphalting, electrical wiring, flooring, plastering, roofing and plumbing are included, as well as the hiring of contractors’ plant and scaffolding. Open-cast coalmining and the erection of overhead line supports and aerial masts are included largely for convenience reasons.