The objective of the research is to establish a methodology to optimise the combinations of passive (building envelope) and active (installations) measures that lead to (extremely) low energy and low pollution residential buildings. Energy consumption and energy savings, environmental impact and costs are considered simultaneously without neglecting the boundary conditions for thermal comfort and indoor air quality and the legal requirements for the energy performance of buildings. The methodology combines advanced evolutionary multi-objective optimisation techniques, life cycle inventory and cost-benefit assessment and is applied to buildings as a whole. Starting from non insulated reference dwellings, the optimisation process is executed in two steps. Firstly, the net energy demand is minimised by optimisation of the building envelope. In the second step, the focus is shifted towards the most effective installation techniques to meet the very low energy demand. The methodology has been used to derive cost-effective energy saving investments in new and retrofitted buildings for the Brussels urban context and to develop concepts for extremely low energy and low pollution dwellings for the Flemish Region. Also the economical optimal combination of energy saving measures and a hierarchy of energy saving investments have been derived.