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U values of typical building methods

U values (overall coefficient of heat transmission) indicate the heat flow through materials - the higher the figure, the higher the heat loss. While the values do vary for each particular material and method of construction, the following table gives general figures for some common modes of construction.

BThU per sq ft, degree F is the imperial unit for quoting U values while watt m2, degree C is the metric (SI) unit. When using these figures, make sure that the appropriate units for area and temperature difference are used.

(If you have any U values for other types of construction, e-mail us and we'll add them)

Wall (outer) BThU per sq ft, degree F watt m2, degree C
9" solid brick 0.38 2.2
11" brick-block cavity - unfilled 0.18 1.0
11" brick-block cavity - insulated 0.10 0.6
Wall (internal)
plaster, 4.5 inch brick, plaster 0.39 2.2
plaster, 4 inch heavyweight block, plaster 0.44 2.5
plaster, 4 inch lightweight block, plaster 0.22 1.2
plasterboard, 4 inch studding, plasterboard 0.32 1.8
Floor (Ground)
solid concrete 0.14 0.8
suspended - timber 0.12 0.7
Floors (Intermediate)
Plasterboard/ 8 inch joist space/ T&g boards - heat flow up 0.29 1.7
Plasterboard/ 8 inch joist space/ T&g boards - heat flow down 0.25 1.4
pitched with felt, 50mm insulation 0.10 0.6
pitched with felt, 100mm insulation 0.05 0.3
flat, 25mm insulation 0.16 0.9
flat, 50mm insulation 0.12 0.7
wooden/uvpc frame, single glazed 0.88 5.0
wooden/uvpc frame, double glazed 0.51 2.9
(the post April 2002 standard)
wooden/uvpc frame, double glazed - 20mm gap, Low-E 0.29 1.7
metal frame, single glazed 1.02 5.8
external solid timber 0.42 2.4
external glazed treat as glazing
internal assume the same as the wall

Note: for conversions
  • multiply BThU, ft 2, degree F by 5.675 to convert to watt m2, degree C
  • divide watt m2, degree Cby 5.675 to convert to BThU, ft 2, degree F