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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 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)
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
 
   
Roof
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
 
   
Window
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
 
   
Door
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
    or
  • divide watt m2, degree Cby 5.675 to convert to BThU, ft 2, degree F