Vertical Greenery Systems (VGS) are relatively new structures for architectural green cladding that embed a curtain of plants (Living Wall -hereafter LW) or grass (Grass Wall -hereafter GW) fixed on building facades and nurtured by an automated watering system. An eMergy evaluation (EE) of both LW and GW was performed aimed at assessing potential 'environmental costs' relative to their manufacturing chain, from plants-grass nursery to the assembling of structural elements, until their sustenance in time. Contextually, benefits were estimated as the energy saving for cooling mainly due to their shading effect and airflow. A 98 m(2) south-oriented facade of a hypothetical 1000 m(3) building has been investigated. EE is an environmental accounting method that accounts for direct and indirect environmental resource use by systems-processes in terms of solar energy equivalents (i.e. solar emergy joule -sej). The Cost to Benefit Ratio has been introduced, as the emergy investment per saved emergy (CBR: sej sej(-1)), in order to compare the environmental cost of structure functioning to the overall energy saving, in emergy terms. Results highlighted that, in certain conditions (i.e. Mediterranean climate, massive envelope, integrated rainVvater harvesting system) both LW and GW can provide net environmental benefits and be valuable options for building retrofitting. (C) 2014 Elsevier B.V. All rights reserved.