The former have their origin or destination outside of the building site, such as resources coming from supply markets, byproducts for secondary markets and waste, whose value or price has to be estimated in order to be incorporated to the works.
Los primeros tienen su origen o destino fuera del centro de producción, tales como recursos provenientes de mercados de suministro, subproductos destinados a su comercialización exterior y residuos que han de valorizados para ser incorporados a la obra.