Present status of the GTC installations design

The maximum exploitation of the excellent astronomical quality of the `Roque de los Muchachos' Observatory is one of the most important design criteria for the GTC Project. The installations of the GTC are being designed in such a way as to minimize local seeing degradation while providing adequate support for the operation and maintenance of the facility. The paper will firstly describe the options that have been adopted as a solution for specific subsystems of the installations, such as: the dome, the auxiliary service areas or the thermal control, with special attention to the environmental conditions in the telescope chamber. Other subjects discussed are: the solutions proposed to minimize the possibility of turbulent surface-layer air negatively affecting astronomical observations; the minimization of wind-induced telescope vibrations and transmission of vibrations between the separate foundations of the buildings and the telescope pier through the ground; the guidelines to carry out the tasks of operating and maintaining the GTC and of course, the solutions for protection against adverse weather conditions.