Energy and Buildings 63 (2013) 1–14 Contents lists available at SciVerse ScienceDirect Energy and Buildings j ourna l ho me page: www.elsevier.com/locate/enbuild Experimental measurements and numerical model for the summer performance assessment of extensive green roofs in a Mediterranean coastal climate F. Olivieri a,∗ , C. Di Perna b , M. D’Orazio c , L. Olivieri d , J. Neila a a Department of Construction and Technology in Architecture, Escuela Técnica Superior de Arquitectura, Universidad Politécnica de Madrid, Av. de Juan de Herrera 4, 28040 Madrid, Spain b Industrial Engineering and Mathematical Sciences Department, Faculty of Engineering, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy c Construction, Civil Engineering and Architecture Department, Faculty of Engineering, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy d Instituto de Energía Solar, Universidad Politécnica de Madrid, Av. Complutense 30, 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 3 December 2012 Received in revised form 23 February 2013 Accepted 30 March 2013 Keywords: Experimental measurements Mediterranean coastal climate Summer conditions Numerical model Thermal resistance High insulated roof a b s t r a c t This paper presents the results of an experimental study carried out on an extensive green roof situated in a Mediterranean coastal climate zone. The aim of the study is to analyze the thermal energy behavior of a green roof during the summer so as to evaluate the effect of vegetation density on the energy performance of the roof and to identify the characteristics of the plants and substrate that have the greatest impact. The paper describes the results of monitoring carried out during the summer in 2010, 2011 and 2012, the development of a numerical model for calculating the thermal resistance of the substrate and the vegetation and the procedure for validating the model using the experimental data. The results show that a green roof which has high vegetation density acts as a passive cooling system when the roof is highly insulated (U value = 0.24 W/(m 2 K)) and that in these conditions the incoming thermal gain is about 60% lower than when the roof has no vegetation. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Although green roofs have been used for a very long time it is only during the last twenty years that there has been an increas- ing interest in their energy and environmental benefits, both for the urban area [1–7] as a whole and for the building itself [8–14]. In fact in recent years many studies have dealt with these aspects from both the qualitative and the quantitative point of view, even if the complexity of the phenomena associated with the thermo- physical behavior of green roofs has meant that no model for analysis which can easily be integrated in the building design pro- cess has yet been developed. For this reason, although green roof technology is well-established [15,16] and the cost of many exten- sive green roof solutions is competitive if compared with other types of roofing [17,18], in many countries green roofs have still not seen widespread use. Above all green surfaces integrated into architectural designs have not yet been regulated by legislation, and ∗ Corresponding author. Tel.: +34 913364239; fax: +34 913366560. E-mail addresses: francesca.olivieri@upm.es, francesca.olivieri.arch@gmail.com (F. Olivieri). no incentives are available for these solutions [19–22]. Many stud- ies concerning the energy effectiveness of green roofs are based on the development of complex mathematical models [23–26] which involve an understanding of the characteristics of the veg- etation and the substrate [27–30]. Generally this goes beyond the know-how of most architects. Moreover, these studies analyze the instantaneous performance of the solution without focusing on its overall seasonal heat balance, although this factor is of great use when a green roof is proposed as an energy efficient solution. On the contrary, research which is based on the observation of moni- toring data often refers to short periods of analysis and the results obtained, although of great interest for understanding the behav- ior of the type of roof analyzed, are difficult to extrapolate for other contexts and for other solutions. Furthermore, in most studies the green roof is considered as a single unit made up of plants and substrate and is always studied when there is the greatest density of vegetation, without bearing in mind that, unless it is a pre- vegetated green roof system, the vegetation takes time to develop after being installed and that the plants may die and the roof may have no vegetation for a certain period of time. Therefore, the aims of this work are (a) to analyze the impact of vegetation density on the energy performance of a green roof 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.03.054