Seasonal Transition Dynamics Of Roof-Induced Thermal Behaviour In A Warm-Humid Tropical Climate: A Field-Based Analysis Of A Non-Ventilated Lightweight Hip-Roof System In Owerri, Nigeria

Abstract

Lightweight residential roofs in warm-humid tropical climates are prone to roof-induced overheating from intense solar exposure and limited attic ventilation. This longitudinal field study monitored a non-ventilated lightweight multiple-hip roof assembly (stone-coated metal roofing over a plaster-of-Paris ceiling with sealed concrete fascia) in Owerri, Nigeria, to characterise how attic-indoor thermal coupling evolves across the dry-to-wet seasonal transition. Paired attic and indoor air temperatures were logged at 6-hour intervals from October 2024 to June 2025, yielding 1,052 synchronised observations. The mean attic-indoor temperature gradient fell from 0.663°C in the dry season (October–March) to 0.401°C at wet-season onset (April–June). Attic and indoor temperatures remained strongly coupled throughout (Pearson r = 0.956; OLS R² = 0.913; Indoor = 9.22 + 0.69 × Attic, autocorrelation-robust 95% CI for slope [0.67, 0.70]), indicating that even under reduced wet-season solar loading, the sealed, non-ventilated attic continued to transmit a substantial share of absorbed heat indoors. Once corrected for a definitional inconsistency in the original calculation, the decrement factor was found to be essentially invariant across seasons (≈0.64), indicating that the effective dynamic attenuation between the monitored attic and indoor environments remained essentially stable across the two seasonal phases, while the magnitude of thermal excitation changed. Concurrent meteorological records available through April showed little change in mean daily solar radiation between the dry-season-dominant period and the initial month of wet-season onset, while relative humidity increased from approximately 70% to 80% and mean air temperature declined from 28.9°C to 28.2°C, indicating that the observed early-season thermal moderation cannot be explained by mean solar radiation alone. These findings underscore the need for attic ventilation, reflective roofing, or radiant barriers in tropical lightweight-roof design. As a single-building case study, findings characterise this specific assembly and should be extended cautiously to other roof configurations.