Thermal Transmittance and Conductance of Roof Constructions Incorporating Fibrous Insulation

Abstract

The paper describes the design and operation of the Ayrement Board's guarded hot box used to measure the thermal performance of insulation materials in a traditional United Kingdom (U.K.) loft construction under controlled air flow and temperature conditions. The reduction in the thermal performance of fibrous loft insulation materials as the mean air flow is increased up to 1.0 ms/sup -1/ over the exposed upper surface is summarized and discussed. The influence of moisture and mass air movement through fibrous materials in modifying the measured surface heat transfer coefficients from the theoretically expected values and the thermal effect of simple modifications to the upper surface that prevent air mass transfer out of the material are examined. Measurements on other materials, such as expanded polystyrene board, are compared with the commonly used U.K. insulation materials. Data on the serious reduction in a material's thermal performance due to the effect of imperfections in laying are presented.