Insulation Basics – Double Brick Walls

I have previously carried out a worked example of the insulation of a Brick Veneer Wall, so as a comparison here is double brick wall.

I have also shown (in brackets) the effect of using a hebel block in place of one of the brick ‘leaves’:


R value

Outside surface air layer


110mm brick


25mm cavity


110mm brick (*or 125mm Hebel Block)

0.08 (*0.81)

Plasterboard 10mm


Inside surface air layer


Total R value


U value = 1/R

1.96 (*0.81)

The heat losses or gains for 150 sq m (fairly typical external wall area) of this type of double brick  wall at 15 degrees above, or below, outside temperature will be:

Area x ‘U’ x temperature difference = watts per hour

150m2 x 1.96 x 15degrees = 4410watts per hour

Heating/Cooling Requirement = 4.41kw/hour

Using Hebel for one of the leaves will improve the heat loss as follows:

150m2 x 0.81 x15degrees = 1822watts per hour

Heating/Cooling Requirement = 1.82kw/hour

Still not as good as the 1.17 kw/hour of the typical brick veneer construction

Don’t forget heat is also lost through windows, ceilings floors and ventilation.


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