P574 SAP Plain Ceiling

A roof U-value calculation is provided for a plain ceiling roof using the Stroma U-value Calculator (version 0.92) and the BS EN ISO 6946 method, printed on 17/06/2019. The roof build-up includes internal surface resistance (0.10 m²K/W), 12.5 mm standard plasterboard (R 0.0595), 100 mm mineral wool quilt (R 2.381) with a bridging element (lambda 0.13, R 0.769) at 9% fraction, 300 mm mineral wool quilt (R 7.143), and external surface resistance (0.04 m²K/W). Total thickness is 412.5 mm and total thermal resistance is 9.723 m²K/W. The calculated average resistance is 9.449 m²K/W. No U-value correction factors are applied. The resulting roof U-value is 0.106 W/m²K, rounded to 0.11 W/m²K.