An additive manufacturing installation has a main housing with an upper part containing a process chamber and a lower part containing a build housing defining an open topped build chamber and containing a build platform in the build chamber, the lower part of the housing having an access opening spaced laterally from the build chamber and an access panel secured over the access opening. A powder dispensing system enables deposition of successive layers of a heat fusible powder over a build plane across the process chamber, adjacent to the build chamber. A directed beam energy source in the upper part of the main housing is operable in a build cycle to selectively scan and thereby selectively sinter or melt powder in a respective defined area of each of successive powder layers. An adjustment device in the build chamber is operable during the build cycle to lower the build platform in the build chamber from an upper position in which an upper surface of the build platform is at or adjacent to the build plane. A holding device is operable to release the build housing, with completion of the build cycle, from a position in which it is retained during the build cycle. With the build chamber released by the holding device and with the access panel moved to open the access opening, a drive system is operable to move the build chamber laterally through the access opening to a position outside the main housing, beyond the access opening.