Emergy based evaluation of environmental performances of Living Wall and Grass Wall systems

•Environmental performance of Vertical Greenery Systems is analysed based on eMergy.•‘Environmental costs’ were assessed as the resource use for maintenance–sustenance.•‘Environmental benefits’ refer to cooling energy saving due to the shading and airflow.•A ‘Cost to Benefit Ratio’ was calculated as an indicator of environmental performance.•In certain conditions environmental benefits were found to balance costs. 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 98m2 south-oriented façade of a hypothetical 1000m3 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: sejsej−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 rainwater harvesting system) both LW and GW can provide net environmental benefits and be valuable options for building retrofitting.