The theme of my work is, how to adapt historic rural houses to the existing requirements for family living. This includes requirements for modifications of the layout, adding new functions and energy savings. Therefore, during reconstructions, the perimeter shell of the house is mainly insulated. Walls, ceilings, floors and roofs are insulated with thermal insulation, windows are replaced with new thermal insulation. These are very expensive measures. Therefore, I wonder if they are all necessary with regard to the return on investment. Moreover, these interventions significantly change the appearance of the building and the whole environment. Based on partial calculations of energy intensity, I look at how individual building modifications are beneficial for reducing energy intensity and whether their benefits are financially worthwhile in view of the costs. I have narrowed my interest to buildings of historical, rural character, which are built from locally available, natural and secondary materials, perfectly adapted to their environment.