The weakest part of concrete high-rise block are their envelopes, so most of regenerations are dealing with reconstruction of existing envelopes. It related of the replacement of window openings, the installation of additional contact thermal insulation or modifications of projecting structures, including loggia glazing and, last but not least, changes in the colour shading of the surface façade layer. These adjustments can improve energy efficiency of the building, but secondary negative effects on the interior environment in terms of the daylight level must also be considered. In this study we tried to take account of both width and shape of jamb of the window with taking into account the effect daylight inside the room.