Several studies analyze the thermal performance of vegetated roofs, presenting either mathematical models or experimental quantifications of heat transfer process through them, also showing the effect of vegetation and soil parameters on the thermal and energy performance of this type of roofing system. However, presently the level of availability of these parameters, has not been enough considered. This work intends to investigate this underestimated issue of the green roofs' thermal modeling, through the consideration of the availability of parameters pertinent to the shortwave radiation exchange, which are adopted by models based on leaf area index (LAI) and on the fractional vegetation coverage (sigma(f)). From the analysis of these models, the importance of a precise knowledge of such parameters arises, despite the availability of their values is still limited. In addition, the absence of a proper database including several green roof plant species and information on their stage of growth, to which a technician possibly will refer in the case of lack of field data, represents quite a worthwhile matter because it may lead to inaccurate estimations of the thermal loads for climatization of buildings equipped with green roofs. In this respect, the manuscript reports an estimation of the errors potentially occurring when not specific vegetation data are used. This evaluation is based on simulations, performed with the DesignBuildere((c)) software, showing the energy effects produced by different assumptions in the green parameters (that is by adopting experimental data revealed by authors and a potential mix of the literature available parameters). Thus, the mission of the paper is to enlighten a difficulty that a technician possibly will encounter when performing an energy and thermal simulation of a green roof; therefore a strong call for making the current database more tailored on green roofs has also arisen. (C) 2016 Elsevier B.V. All rights reserved.