ENERGY EFFICIENCY IN THE LIFE CYCLE OF BUILDING AS A MITIGATION ACTION OF CLIMATE CHANGE. CASE STUDY ON THE EXAMPLE OF THE KINDERGARTEN BUILDING IN SIERAKOWICE VILLAGE. Abstract This article is an attempt to present the complex issue of energy efficiency in the field of architectural design, which was presented on the basis of a case study - a kindergarten in the village of Sierakowice. The building was realized in wooden technology, to minimize its impact on the natural environment. The facility is equipped with a number of devices for obtaining renewable energy (photovoltaic panels, wind turbines, heat pumps and ground heat exchangers). The author's analysis of the data in the author's opinion shows that the energy balance is not only the issue of the efficiency of energy-producing devices and energy consumption in the use phase. The content of the paper attempts to show that efficiency is rather the sum of energy generated and consumed in the use phase, but also in the phase of materials production, building implementation and its utilization. While in these periods of "life" of the building we deal mostly with the use of energy (negative balance), in the phase of use, energy can be produced. In this context, it can be assumed that the energy balance is not constant for a specific investment; it may change depending on the amount of energy produced and the variable efficiency of the devices used. The conclusion from the presented research is therefore the statement that the energy efficiency of the building is a variable function over time, and consequently, a building with zero energy consumption in a holistic approach can be easily implemented.