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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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References

1 Chartered Institution of Building Services Engineers, CIBSE Guide, Volume A, Sections A5 and A9, London (1979).

2 Siviour, J. B. , Areas in building heat loss calculations, BSER & T, 6 (3), 134–136 (1985).

3 Chartered Institution of Building Services Engineers, CIBSE Guide, Volume A, Section A3, London (1980).

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10 BS 5250, Code of basic data for the design of buildings: the control of condensation in dwellings (1975) with amendments, (1979 and 1983).

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11 GLC Bulletin 142, Condensation: prevention better than cure, Building Technical File N6 33–39 (1984).

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12 Oughton, R. J. , Loft insulation and condensation in roof spaces, BSER & T, 3 (1), 40–42 (1982).

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13 Sanders, C. H., Private communication, Building Research Establishment, East Kilbride, Scotland (1985).

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14 Saunders*, C. H. , Air movement in houses: a new approach, Building Research and Practice, 160–175 (May/June 1982).

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15 BRE Digest 306, Domestic draughtproofing: ventilation consideration, Building Research Station, Watford (1986).

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16 Chartered Institution of Building Services Engineers, CIBSE Guide, Volume A, Section A2, London (1982).

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17 Barratts (Aberdeen) Limited, Private communication (Oct 1986).

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18 Wellgrove Timber Systems Limited, Westhill, Aberdeenshire, Component specification for a Wellgrove house kit, Trade Literature and Private communication (Oct 1986).

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19 Dow Construction Products, Solihull Roofmate PR: Pitched Roof Insulation, Trade literature (Nov 1985).

Heat loss from pitched roofs

Abstract

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