In Situ Construction

Housing built on-site is sometimes called in situ house construction. This is the dominant method of residential construction, including multifamily housing. The approach refers to building in which a greater proportion of work on the final house assembly is accomplished on-site compared with work done off-site. Since the light wood frame was first used in the 1830s, a gradually increasing percentage of value added to elements used in house building has migrated off-site. Today, a site-built house may have prefabricated floor and roof trusses, windows, fireplaces, and kitchen and bathroom elements. Although foundations remain largely site operations, new products are being introduced to speed foundation work. Developments in [Page 386]mass-produced items, such as new exterior and interior finishes, structural elements, glazing, prehung doors, fasteners and sealants, and heating, ventilation, and air-conditioning systems, have also helped increase the efficiency of site building.

There are basically two classes of site builders. One is “production homebuilders,” large organizations that may also have a modular and panelized division and may operate in multistate or national markets. The other is “small-volume homebuilders,” who build, on average, fewer than 50 houses each year and who focus on local markets. A large number of single-family houses are built by contractors, sometimes called “pickup truck” builders, who build one house at a time on a speculative basis, operating from their home offices with very low overhead and no permanent construction crew.

Both types of site builder have adopted rationalization procedures to increase their efficiency in competition with builders using the output of modular and panelized producers. This has included improvements in scheduling and management, arrangements with suppliers, computer-assisted design and accounting, and the adoption of new tools and material that speed work, reduce the labor component, and improve quality.

Also part of in situ building is remodeling activity, which accounted for more than $112 billion in expenditures in 1996. This activity includes both rented and owned units, single-family and multifamily units, and construction improvements and upkeep.

In situ residential construction volume is difficult to quantify because it uses both prefabricated and mass-produced elements and may thus be counted as panelized housing or “industrialized housing” in some documentation.