In Algeria, the rapid increase in population and urbanization, evolving comfort needs, subsidized electricity prices, and climate change has significantly contributed to higher energy consumption for heating and cooling as well as greenhouse gas emissions, particularly in southern regions characterized by hot and arid climates. Most recent constructions in Algeria are highly energy-intensive, unlike traditional Saharan architecture, which is far more environmentally friendly. This paper presents eco-friendly and cost-effective design methods and solutions inspired by Saharan architecture to guide architects and project owners during the design phase of buildings in hot climate regions. A numerical simulation was performed using EnergyPlus 9.2 to compare the energy consumption of a semi-collective residential building in Béni Abbès with four design alternatives inspired by vernacular architecture, “O”, “L”, “U”, and rectangular configurations. The findings showed that the O-shape configuration achieved the highest cooling energy savings (38.55% on the ground floor, 27.68% on the first floor), followed by the L-shape (31% and 32%), U-shape (28% and 29%), and rectangular shape (26% and 25%), highlighting the effectiveness of form optimization in enhancing energy efficiency. The results obtained demonstrate the energy efficiency of the four variants compared with the initial cases, with a reduction in cooling needs while using the same materials. This reduction could reach up to 39% during the hot season. The pay-back period for the investment was estimated at approximately six years for the city of Béni Abbès and around five years for the city of Adrar. By incorporating full insulation into all four variants, a maximum reduction in air conditioning consumption of approximately 53% was observed for the “O” variant in Béni Abbès compared with the initial case without insulation. In Adrar, this reduction reached around 48% for the same variant. Passive design elements, such as shape optimization, compact urban fabric, patio integration, and window shading, offer moderate energy savings with a shorter payback period, whereas complete insulation achieves higher energy savings but requires a longer time to offset the investment costs.

This study proposes a sustainable multi-criteria optimization framework for the energy retrofit of collective residential buildings in Algeria, particularly those constructed between the 1970s and 1980s. Through on-site surveys, energy consumption analysis, and seasonal temperature measurements, the high energy demand of these buildings was confirmed. Using EnergyPlus simulations based on Meteoblue weather data, 16 retrofit strategies were assessed—incorporating various insulating materials applied internally or externally (via rendering or cladding). The ELECTRE III decision-making tool was employed, supported by the Simos Revised Framework (SRF) for weighting environmental, economic, and social criteria. Results demonstrate that all strategies significantly reduce energy demand—by up to 72.5%, with reductions reaching 94.4% in winter and 43.5% in summer, depending on insulation type and placement. Improvements in indoor thermal comfort were also observed, with exterior insulation beneath cladding offering the best performance during winter, while exterior rendering also proved effective in the summer. The ELECTRE III analysis identified rock wool and polyurethane with fiber cement cladding as optimal insulation solutions. The proposed approach supports national energy policies and aligns with the Sustainable Development Goals (SDGs), offering a replicable model for large-scale building retrofits in similar climatic and architectural contexts.