Official definition
This subsector comprises establishments primarily engaged in trade activities generally needed in the construction of buildings and structures, such as masonry, painting, or electrical work. The work performed may include new work, additions, alterations, maintenance, and repairs. Specialty trade contractors usually work under contract to general contractors or operative builders to carry out a component of an overall project. However, they may contract directly with the owner of the property, especially in renovation and repair construction. Not all specialized trade activities are classified in this subsector. In order to conform to the generally accepted distinctions made by construction businesses themselves, some types of specialized establishments involved in heavy and civil engineering construction are classified in subsector 237 Heavy and civil engineering construction. Usually most of the work is carried out at the construction site. Some trade contractors operate shops in which they carry out job-specific prefabrication and other work. However, establishments that manufacture structural components such as steel and pre-cast concrete, or that manufacture building equipment such as boilers and elevators, are classified in sector 31-33 Manufacturing even if they install these goods themselves. The specialized activities classified in this subsector range from the initial site preparation for new construction, through the construction of building foundations and structures, the installation of building equipment and systems, to the finishing of buildings and other structures.