Sustainable Retrofit Pathways for Post-War Lamella Residential Buildings: A Comparative Energy Performance and Life Cycle Assessment in Novi Beograd, Serbia

This paper evaluates the energy performance and lifecycle environmental impact of three retrofit pathways—conventional insulation, an extensive green roof, and rooftop photovoltaics—for two lamella-type residential buildings (three-story, five-story; over 40 years old) in Blocks 45 and 70, Novi Beograd, Serbia. The study builds on an architectural concept treating the flat roof as an active environmental surface. Energy demand was quantified via calibrated dynamic simulation for a baseline and three scenarios—insulation (S1), insulation with an extensive green roof (S2), and insulation with rooftop photovoltaics (S3)—with environmental performance assessed using cradle-to-use LCA (1 m2 heated floor area, 50-year period) covering global warming potential, cumulative energy demand, and Environmental Footprint 3.1 indicators. Insulation and the green roof achieve nearly identical reductions in heating demand (27–31%) and lifecycle GWP/CED (10–13%), the green roof performing marginally better while also offering evapotranspirative cooling and urban co-benefits. Photovoltaics deliver the largest lifecycle GWP reduction (26% three-story, 15% five-story) and cut acidification by up to 36%, but increase mineral resource depletion, water and land use. Benefits of both roof-level measures scale with roof-to-floor-area ratio, favoring lower-rise buildings, supporting prioritization of green roof and photovoltaic retrofit across the district lamella stock.