Building Energy Optimization Using Climate-Responsive Design and Lightweight Cementitious Materials in Residential Projects

Purpose: This study examines the energy inefficiencies of residential buildings in Pakistan, where poorly sealed envelopes and non–climate-responsive architectural practices result in excessive cooling loads. It aims to develop and validate, for the first time in Pakistan, a climate-responsive retrofit design framework integrating passive envelope optimization with experimentally verified Lightweight Aggregate Concrete (LWAC) to improve thermal performance and support sustainable housing in hot–humid climates. Design/Methodology/Approach: A representative 351.45 m² single-family dwelling was modelled in DesignBuilder using IWEC climate data for Karachi and Multan and calibrated against local residential load profiles. A comprehensive retrofit package—comprising R-20 roof and wall insulation, a reduced window-to-wall ratio (15%), low-U double glazing (1.5 W/m²·K), external shading, passive cooling, and enhanced cross-ventilation—was evaluated. LWAC samples were laboratory-tested for density, thermal conductivity, and compressive strength to assess their suitability as envelope materials. Findings: The integrated framework reduced Energy Use Intensity from 181.18 to 71.24 kWh/m²·year (60.7% reduction), equivalent to 38,639 kWh/year of avoided energy use, 377,188 PKR/year in utility savings, and 19,320 kg CO₂/year in avoided emissions. LWAC demonstrated 15–20% lower density, ~48% lower thermal conductivity, and ≥30 MPa compressive strength, confirming its structural adequacy and enhanced thermal resistance. The combined retrofit and LEED v4 measures resulted in a net premium of 336,298 PKR with a simple payback of 0.89 years, reduced to <0.7 years under a 6% annual tariff escalation. Implications/Originality/Value: The study provides the first validated climate-responsive retrofit and LWAC integration framework for Pakistan’s residential sector, demonstrating that high-performance, low-carbon housing is technically feasible, cost-effective, and rapidly scalable using local materials. The findings directly support ECBC-2023 implementation and offer evidence-based guidance for policymakers, designers, and developers seeking to promote sustainable construction in hot-humid regions