The development of new infrastructure increases energy consumption consequently, the need for nature-based solution arises. Motivation for modular green systems (MGs) are rooted in making the existing buildings more environmentally friendly. This work aims to investigate MGs, prefabricated greenery systems as a retrofitting approach to minimize energy consumption in buildings. Initially, façade and roof alternatives were designed with different plants, materials, and sizes. The investigation covers two levels: firstly, the product level, i.e., life cycle analysis that entails evaluating the energy consumption and CO2 footprint of the system. Plastic, recycled plastic, cork, and fiberglass module materials were evaluated using Granta Edupack for the stages of extraction, manufacture, transport, and disposal. Recycled plastic is the best in terms of environmental impact along its lifespan. Secondly, recycled plastic was applied with the retrofit alternatives for roof; RA1, RA2, and RA3 and façade; FA1, FA2, and FA3. Investigation on energy performance was conducted for an existing building, i.e., Faculty of Architecture, E block of IYTE using DesignBuilder software. Green roof and façade modules showed 4.46-6.52 % and 7.44-11.72 % heating consumption reduction range, respectively. Applying RA2 on all the roof area (ARA2) and FA3 on south façade (SFA3) save 12.65 % of 2773 kWh heating consumption and 1.60 % of 7555 kWh cooling consumption, ultimately saving 471.58 kWh on monthly average. To conclude, MGs can be an alternative to the retrofitting strategies due to providing lower environmental impact, reduced consumptions for heating energy on building basis and reduced cooling consumptions on city scale.