Making the building at Leidseplein 36 / 36 RD in Haarlem more sustainable to energy label A / A+. In general, this involves a complete insulation of the outer shell; first floor insulation underneath, insulation of the outer walls, insulation of the attic floor and the roof of the temporary extension at the rear. The roof of the temporary extension and all other flat roofs will receive a retention roof: sedum planting on top of the new insulation. In addition to the complete preservation of the building, overdue maintenance needs to be done. Especially the wooden joists on the first floor are partly in a bad condition, some need to be replaced completely and others partly. A thorough inspection of the crawl space is necessary also the natural ventilation of this crawl space must be repaired. The attic space will be transformed into a team room, library and office spaces.