Assessment of building envelope thermal insulation and indoor air temperature

Abstract

This study investigated the impact of thermal insulation placement, type and thickness on indoor air temperature (IAT), energy performance and electricity costs for a residential villa in the hot-humid climate of Jazan, Saudi Arabia. A baseline EnergyPlus model, validated against measured data from Riyadh, revealed that without insulation, IAT exceeded American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) comfort limits for 93 % of the year. Simulations of five common insulation types, including board, batt, cellular glass, fibreglass and polyurethane, demonstrated that exterior placement consistently outperformed interior installation by reducing heat transfer and infiltration. Polyurethane delivered the highest performance, achieving up to a 40,2 % reduction in annual energy use at 100 mm thickness, with diminishing returns beyond 75-100 mm. A floor-level analysis revealed that upper floors with exposed roofs required thicker insulation to counteract solar gains, whereas lower floors performed optimally with thinner layers in humid conditions. An economic analysis based on Saudi Arabia’s residential tariff structure demonstrated lifetime savings exceeding USD 79.760,00 over 20 years for top-performing configurations. The findings underscore the importance of climate- and building-specific insulation strategies to optimise both thermal comfort and long-term economic returns.