Calculations of building retrofit effectiveness have shown that the replacement of original windows with new ones is not as effective in terms of heat energy saving as are the insulation of a roof, walls and other improvements because the investments are large and take a long time to be repaid. However, in addition to energy saving, window replacement improves the indoor climate of the building, its interior and architectural appearance as well as its market value. The sequence of building operations determines when the replacement of windows should be done. When financial resources are limited, managers of public buildings often begin the renovation of a building's envelope with the replacement of windows. The client faces some problems in choosing among the great variety of windows to satisfy his/her needs, especially with respect to the cost-quality relationship. The method of multiple criteria complex proportional assessment (COPRAS) developed by the authors aims at solving the above-mentioned problems. The solutions based on multicriteria analysis allow for a more rational and realistic assessment of customer's needs as well as cutting down window renewal costs. In this paper, practical example (key-case) of selecting a contractor for the replacement of windows in the main building of Vilnius Gediminas Technical University (VGTU) is presented as a part of its retrofit multivariant design. (c) 2005 Elsevier B.V. All rights reserved.