Thermal Losses  
Thermal Losses are generally categorised as


Annual Heating Energy Requirement  
The annual heating requirement may be derived by multiplying


Thermal Conductivities of common building materials These are typical values. Use product data where available.  
Material  Conductivity (W/m^{2o}C)  Resistance of 1cm thickness(m^{o}C/W)  
Aluminium  211  0.00005  
Brick  1.0  0.01  
Concrete  1.5  0.007  
Gypsum plaster  0.25  0.04  
Softwood  0.12  0.08  
Copper  385  0.00003  
Glass  1.0  0.01  
Polystyrene  0.04  0.25  
External surface high emissivity    0.06  
Internal surface high emissivity    0.12  
Calculating U values One fairly straightforward way is to use the table on the previous page (or generate one yourself).  
Multiply the number of centimetres thickness of each layer by its 1cm thick resistance add the resistances obtained for each layer add external and internal resistances invert the answer 
10 x 0.01, 5 x 0.25, 0.04 0.1 + 1.25 + 0.04 = 1.39 1.39 + 0.12 + 0.06 = 1.57 1/1.57 = 0.64W/m^{2o}C  
Calculating U values for constructions with cavities  
 
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