Abstract
In the calculation of heat loss from a pitched roof it is usual to disregard gable areas, insulation location, loft space ventilation and air leakage from the dwelling, as advocated by the CIBSE. The CIBSE method does assume a general loss due to infiltration, but not specifically through the loft. In this paper the problem is analysed by considering steady-state energy transfer to and from the loft space as a function of various ventilation and air leakage (from dwelling) rates, gable heat transmittances, and the extent and location of insulation. The effects of loft ventilation and gable heat transmittance are negligible when the insulation is located entirely at the ceiling level. However, the CIBSE procedure underestimates the heat loss significantly when the insulation is partially or entirely at the roof level. Air leakage from the dwelling contributes significantly to the heat loss from the ceiling in all cases, but its effect on the building heat loss is included in the conventional method in the form of a general heat loss due to infiltration.
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