Pre-erection work; new construction and repair, alteration, restoration and maintenance work on residential buildings, non-residential buildings or civil engineering works. This work can be carried out either by general contractors who do the complete construction work for the owner of the project, or on own account; or by subcontracting parts of the construction work to contractors specializing, e.g., in installation work, where the value of work done by subcontractors becomes part of the main contractor's work. The products classified here are services which are essential in the production process of the different types of constructions, the final output of construction activities.