Diurnal and Seasonal Heat Gain in an Unventilated Attic Beneath a Stepped-Tile Corrugated-Aluminum Roof: Field Evidence from a Hip-Roofed Residential Building in a Warm-Humid Nigerian Climate

Abstract

Lightweight, uninsulated roof assemblies dominate residential construction across the warm- humid-tropical housing estates of southeastern Nigeria, yet the thermal behaviour of the attic cavities they create remains poorly characterised in the field. This study reports a 212-day, temperature-synchronised field investigation of an unventilated attic beneath a multiple-hip, stepped-tile corrugated-aluminium roof on timber trusses, with a plaster-of-Paris suspended ceiling, in the Federal Housing Authority Estate, Owerri, Imo State, Nigeria. The roof has no ridge, eave, or hip venting. Two calibrated single-channel data loggers recorded attic and indoor air temperature at a fixed 6-hour interval from 1 October 2024, and were synchronised with daily air temperature, solar radiation, and relative humidity records from the co-located Imo State University meteorological station for the overlapping period 1 October 2024 to 30 April 2025 (n = 212 days; 848 six-hourly attic readings). Over this period the attic recorded a mean temperature of 31.18 ± 1.39 °C against an ambient mean of 28.83 ± 1.45 °C, a persistent excess of 2.35 °C, with an absolute peak of 39.5 °C (10 March 2025) and a mean afternoon (14:00 h) reading of 35.97 ± 1.95 °C — 6.8 °C above the concurrent morning value. Attic maxima correlated positively with incident solar radiation (r = 0.60, p < 0.001) and attic diurnal amplitude scaled strongly with radiation (r = 0.67, p < 0.001), while relative humidity was weakly negatively associated with attic temperature (r = −0.29). The attic exceeded 34 °C in 22.3% of six-hourly readings, 36 °C in 15.2%, and 38 °C in 2.1%, generating an estimated 26,324 cooling-degree-hours (base 26 °C) over the monitoring period. These results demonstrate that a fully sealed hip-roof attic under stepped-tile aluminium sheeting behaves as an efficient, low-mass solar collector that stores and re-radiates substantial heat toward the POP ceiling, and they provide the first long-term, multi-season field baseline for unventilated hip-roof attics in the Nigerian humid tropics. Implications for ceiling heat flux, attic ventilation retrofit, and reflective roofing strategy are discussed.

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