In recent years school buildings, containing the workshop in high school, are old in Japan. Therefore most of them need renovating. Any air-conditioning systems are not often installed in the workshops. Workshops without air-conditioning systems often have bad indoor thermal environments. Since bad thermal environment is exhausting and likely to cause some accidents, eco-renovation method for improvement of thermal environment is required. In this paper, various kinds of eco-renovation methods are examined by CFD simulation. The examined methods are insulation of the PC roof and the walls to decrease the surface temperature, and utilization of more ventilation rate in summer.