9th International Conference LCA of Food San Francisco, USA 8-10 October 2014 Environmental assessment of urban horticulture structures: Implementing Rooftop Greenhouses in Mediterranean cities Esther Sanyé-Mengual 1,* , Jordi Oliver-Solà 1,2 , Assumpció Antón 3,1 , Juan Ignacio Montero 3,1 , Joan Rieradevall 1,4 1 Sostenipra (ICTA-IRTA-Inèdit) – Institute of Environmental Science and Technology, Universitat Autònoma de Barcelona (UAB), Campus de la UAB, 08193, Bellaterra (Spain) 2 Inèdit. Inèdit Innovació SL, UAB Research Park, Crta. de Cabrils, km2 (IRTA), 08348, Cabrils (Spain) 3 Institute of Research and Technology in Agrifood Sector (IRTA), Environmental horticulture, 08348, Cabrils (Spain) 4 Departament of Chemical Engineering, UAB, Campus de la UAB, 08193, Bellaterra (Spain)  Corresponding author. E-mail: Esther.Sanye@uab.cat ABSTRACT The Rooftop Greenhouse (RTG) of the Rooftop Greenhouse Lab (ICTA-UAB) is analyzed from an environmental perspective as a new form of urban agriculture. The global warming potential of an RTG structure was 2.5 kg of CO2 eq., while the cumulative energy demand was of 46.4 MJ, considering a functional unit of 1m 2 and 1 year. When comparing the RTG structure with a multi-tunnel greenhouse, these values resulted in 80% and 53% higher, respectively. 1 kg of tomato produced in an RTG had a GWP of between 178 and 297 g of CO2 eq. and a CED of between 2.9 and 4.8 MJ, depending on the crop yield. When compared with the horticultural production in a multi- tunnel greenhouse, 1 kg of tomato can be 33% less impacting or 25% more impacting for the GWP and 31% less impacting or 26% more impacting for the CED. Keywords: rooftop farming, greenhouse technology, urban agriculture, smart cities 1. Introduction Urban agriculture (UA) is spreading over the urban areas of developed countries in response to a growing awareness of the environmental impact of food systems (Howe and Wheeler 1999; Cohen et al. 2012; Mok et al. 2013). UA types are numerous and vary in placement, property and aim, such as community gardens for social inclusion, private backyard gardens for self-supply and public-property spaces for individual small gardens. Nowadays, UA is also colonizing buildings through building-based UA forms. These forms of UA have been de- fined by multiple authors as Vertical Farming (Despommier 2010), Skyfarming (Germer et al. 2011), Building- Integrated agriculture (Caplow 2009) or Zero-Acreage Farming (Specht et al. 2014). Within the multiple forms of building-based UA, rooftop farming is the most common since rooftops are cur- rently unused spaces that can be occupied and revalorized. Rooftop Greenhouses (RTGs) are greenhouses built on the rooftop of buildings devoted to, mostly, horticulture production (Cerón-Palma et al. 2012). Up to now, several companies in North America have built RTGs for their local production businesses. Gotham Greens (Brooklyn, New York) or Lufa Farms (Montreal) sell different kind of vegetables that have been produced in RTGs of 1400 m 2 and 2900 m 2 , respectively, by offering, thus, km.0-products that avoid food-miles. 1.1. Current research on rooftop greenhouses Only few studies have focused on rooftop greenhouses as urban horticulture systems. Cerón-Palma et al. (2012) identified the barriers to and opportunities of implementing RTGs in the Mediterranean region, by per- forming discussion groups with experts on architecture, agronomy and urban sustainability. Specht et al. (2014) did a literature review of urban horticulture in and on buildings, including RTGs, to determine the potentialities and limitations of these systems. Both studies found opportunities in the three pillars of sustainability: environ- ment (e.g., reducing food-miles and transport emissions), society (e.g., improving community food security) and economy (e.g., revaluation of unproductive spaces). Notwithstanding the large potential benefits, barriers were also noted. Particularly, the studies highlighted social (e.g., lack of acceptance) and economic limitations (e.g., investment costs). Sanyé-Mengual et al. (2013) quantified the potential environmental benefits of the local food production in terms of the avoided distribution of products from RTGs in Barcelona. A kilogram of tomato produced in a RTG in the city of Barcelona could substitute 1 kg of tomato from Almeria (1000 km), where 60$ of the tomatoes consumed in Barcelona are produced. The local production could avoid 441 g of CO2 eq. and 12 MJ of energy per kg due to the optimization of the packaging use, and the reduction in the transport requirements and in the