The paper presents the energy evaluation of urban structures and the dimensioning of building sites using the iso-shadow method. Iso-shadows represent the ratio of incident solar radiation on a building or land to unobstructed solar radiation received at the same location during the chosen period of time, day or year, respectively. This method enables quantitative evaluation of energy efficiency of the selected layout organisation. For the calculation of thermal how the computer tool 'SENCE' (SHADOWS), developed at the Faculty of Civil and Geodetic Engineering at the University of Ljubljana, was used. Various building structures were investigated, First a building with reference floor geometry (length 60 m, width 12 m, height 6 m) was simulated. The site layout consisting of four parallel reference buildings was designed, taking into account the chosen minimum duration of solar radiation during the year, calculated with the iso-shadows module of the 'SENCE' programme. Then the building width was increased to 24 m and 36 m, respectively. Also the building height was varied in three steps, 6 m, 12 m and 18 m. The results of the simulations are presented in the form of iso-shadow charts. The comparison between various building types was made, taking into account: modified orientations, monitored density of residents and changed site size due to different building types. The evaluation of the results was carried out and the advantages and disadvantages of various building types are discussed. It was found that building width and height substantially influence the required site size, site layout and resident density. (C) 2000 Elsevier Science Ltd. All rights reserved.