Day and Night Thermal Stress and Implications for Building Designs in South-West Nigeria

Abstract

Understanding diurnal thermal stress patterns is fundamental to the design of climate-responsive buildings in the humid tropics. This study investigates day and night thermal stress conditions across six state capital cities in Southwest Nigeria, namely Ibadan, Akure, Ado-Ekiti, Osogbo, Abeokuta, and Lagos, and translates these findings into location-specific architectural design prescriptions. Eight years of monthly climatic data (2016 to 2023) obtained from the Nigerian Meteorological Agency (NiMet) were analysed using a hybrid framework integrating the Evans Comfort Scale and Mahoney Tables. The Evans Comfort Scale classified each month into thermal stress levels ranging from very cold to very hot for both daytime and nighttime conditions. The Mahoney Tables were subsequently applied to convert climatic indicators into prescriptive building design guidelines encompassing layout, spacing, ventilation, openings, wall and roof construction, and rain protection. Results reveal that daytime very hot stress conditions prevail across all six cities during the dry season months of November through April, with Abeokuta recording the most severe profile at a peak maximum temperature of 37.2 degrees Celsius for eight months annually. In contrast, nighttime conditions are predominantly cold to comfortable across all study locations throughout the year, indicating a substantial diurnal temperature range that creates significant passive cooling opportunities through night ventilation strategies. A bimodal stress pattern characterises most inland cities, while Lagos exhibits a more attenuated coastal thermal regime. Design implications include the universal necessity for east-west building orientation, single-banked room arrangements for permanent cross-ventilation, medium to large openings on north and south facades, effective shading devices, and differentiated wall and roof specifications responsive to local humidity groups. These findings provide the first multi-city, empirically grounded, diurnal thermal stress atlas for Southwest Nigeria and offer an actionable evidence base for revising the Nigeria Building Energy Efficiency Code and developing location-specific passive design standards for tropical institutional and residential buildings.