The paper presents an approach to evaluating a building throughout its whole life cycle in relation to its sustainable development. It describes basic tools and techniques of evaluating and analysing the costs in the whole life cycle of the building, such as Life Cycle Assessment, Life Cycle Management, Life Cycle Cost and Social Life Cycle Assessment. The aim of the paper is to propose a model of cost evaluation throughout the building life cycle. The model is based on the fuzzy sets theory which allows the calculations to include the risks associated with the sustainable development, with the management of the investment and with social costs. Costs incurred in the subsequent phases of the building life cycle are analysed and modelled separately by means of a membership function. However, the effect of the analysis is a global cost evaluation for the whole life cycle of the building.

Accommodation tourist industry is characterized by high variability. For this category of services not only the location is crucial- that does not change, but also the standard, prices and seasonality of services. In the recent years, leisure centers performing functions only during the summer time have seen the possibility to extend their activities beyond the summer months. The reasons for this are the local investments requiring qualified staff which comes from different parts of the country, Europe and the world while creating dernand for accommodations. To meet the possible demand needs and to adapt to cold season, performing thermo-modernization works is necessary. In order to find the best solution and answer those needs, analysis of the profitability of the investrnents in a chosen holiday resort was carried out. The article presents the results of the analysis based on the payback period, LCC analysis and assessment of the investments risk.

Planning maintenance costs is not an easy task. The amount of costs depends on many factors, such as value, age, condition of the property, availability of necessary resources and adopted maintenance strategy. The paper presents a selection of models which allow to estimate the costs of building maintenance, which are then applied to an exemplary office building. The two of the models allow a quick estimation of the budget for the maintenance of the building, following only indicative values. Two other methods take into account the change in the value of money over time and allow to estimate, assuming the adopted strategy and assumed costs, the value of the current amount allocated to the maintenance of the building. The final model is based on the assumptions provided for in Polish legislation. Due to significant simplifications in the models, the obtained results are characterized by a considerable discrepancy. However, they may form the basis for the initial budget planning related to the maintenance of the building. The choice of the method is left to the decision makers, but it is important what input data the decision maker has and the purpose for which he performs the cost calculation.

The main goal of the studies was to collect information on the impact of the identified risk factors on the amount of costs incurred in the life cycle of buildings. The own studies were focused especially on residential and non-residential buildings. The studies consisted in obtaining expert opinions on the subject of the research involves in the non-random (arbitrary) selection of a sample of respondents from among specialists corresponding to the industry purpose of the studies and the research material. The research used the expert questionnaire method. The studies were divided into three stages. In the first stage, the identification and division of risk factors in the life cycle of buildings was performed. Then, experts assessed 45 selected risk factors that may affect the amount of costs incurred in the life cycle of buildings. In the last step, the research results were developed in the form of a checklist knowledge base, containing information about the potential impact of the identified risk factors in the life cycle of buildings on the amount of the corresponding components of life cycle costs.

The model for estimating the whole life costs of the building life cycle that allows the quantification of the risk addition lets the investor to compare buildings at the initial stage of planning a construction project in terms of the following economic criteria: life cycle costs (LCC), whole life costs (WLC), life cycle equivalent annual costs (LCEAC) and cost addition for risk (ΔR_LCC). The subsequent stages of the model development have been described in numerous publications of the authors, while the aim of this paper is to check the accuracy of the model in the case of changing the parameters that may affect the results of calculations. The scope of the study includes: comparison of the results generated by the model with the solutions obtained in the life cycle net present value method (LCNPV) for time and financial input data, not burdened with the risk effect; the analysis of the variability of results due to changes in input data; analysis of the variability of results as a consequence of changing the sets of membership functions for input data and methods for defuzzification the result.