Youth housing prototypes are widely spread all over Egypt as a cheap economic housing for youth which are designed in a number of different shapes. A post occupancy evaluation (POE) has been conducted to one of these prototypes to assess some modifications spontaneously done by users to the original design for the sake of enhancing building performance, e.g., creating new openings to improve lighting and natural ventilation thermal comfort, and making sunshades to control direct sunlight and thermal radiation. These assessments have been validated using simulation techniques i.e. CFD, thermal and daylight simulations, to compare natural ventilation, thermal comfort, and daylight energy efficiency in the original designs to that in the user modified. A wind tunnel test has been conducted to validate the standardk–epsilon turbulence CFD simulation in addition to daylighting in-situ measurements to validate natural lighting. The outcome of this research could be widely used as an important feedback tool in the future designs of the same prototype to evaluate user behaviour role in building performance efficiency. The research showed that some of these behaviours has improved thermal comfort by 60％ to 87％ from the original design while daylight efficiency has been improved by 31.8％ to 41.4％ while sensible cooling loads’ improvement ranges from 27.4％ to 77.2％ for the north zone and 29.9％ to 91.6％ for the south one, and thus, it could be used as a reliable POE feedback tool.