This research provides insight into difficulties encountered by housing associations if they decide to implement energy-saving measures in building complexes inhabited by tenants as well as owner-occupiers. The urgency of this topic is high considering the effects on the environment, the rising energy prices and the increasing number of these so-called mixed complexes. The difficulties are scrutinized in a literary study and through interviews with several housing associations. The research shows that difficulties may occur on three different areas: juridical, financial and technical. Most of the complications can be mitigated by preventive or curative measures. Preventive measures can be used in homogeneous complexes to avoid future problems. The curative measures to reduce current problems are translated into two models. One model focuses on solutions in juridical field, the other one on those in financial field. Using these models could improve the efficiency of the procedures and the measures taken by housing associations.