Finding cost-optimal solutions towards nearly-zero-energy buildings (nZEBs) in accordance with European energy performance of buildings directive (EPBD-recast 2010) is a challenging task. It requires exploring a huge number of possible combinations of energy-saving measures (ESMs) and energy-supply systems including renewable energy sources CRESS), under a comparative framework methodology. The current study introduces efficient, transparent, and time-saving simulation-based optimization method for such explorations. The method is applied to find the cost-optimal and nZEB energy performance levels for a study case of a single-family house in Finland. Different options of building-envelope parameters, heat-recovery units, and heating/cooling systems as well as various sizes of thermal and photovoltaic solar systems are explored as design options via three-stage optimization. The resulted economic and environmental trade-offs show that primary energy consumption >= 93 and <= 103 kWh/m(2)a is a cost-optimal energy performance level. It is economically feasible to achieve nZEB with 70 kWh/m(2)a. However, incentives (e.g., energy credits) are required to reach lower-environmental-impact houses. Investing in low-operating-cost environmentally friendly heating system (e.g. ground source heat pump) is a key element for optimal solutions. The optimal implementation of ESMs and RES depends significantly on the installed heating/cooling system and the escalation rate of the energy price. (c) 2012 Elsevier B.V. All rights reserved.