Thermal Properties of Brick Cavity, Brick Veneer and Weatherboard Walls

The thermal transmittance and thermal resistance of three various types of domestic dwelling walls are compared. The wall types are:

•         Brick Cavity – consisting of two walls of 110mm thick extruded bricks separated by a 50mm air space

•         Brick Veneer – walls constructed from an outer layer of 110mm thick extruded bricks, with an inner wall of 12mm plaster board separated by a 140mm air space housing the studs

•         Weatherboard – consisting of 20mm thick weatherboards, 100mm air space and 12mm thick plaster board

Values are also supplied for insulated walls with the above constructions. Insulation for the various wall types are as follows:

•         Brick cavity – 2 layers of 110mm thick extruded bricks separated by 70mm of urea formaldehyde

•         Brick Veneer – 110mm exterior extruded brick wall, backed up by 50mm air space, 50mm of bulk insulation, 40mm of air space, reflective foil and 12mm of plaster board respectively

•         Weatherboard – 20mm of weatherboard, 50mm of air space, 50mm of bulk insulation, 40mm air space, reflective foil and 12mm of plaster board.

The thermal resistance (R) is a measure of the resistance to heat flow through a wall and is also an indication of heat loss. It should be noted that the R-value is not just the sum of the R-values for the individual elements. Other factors must be taken into consideration in wall measurements such as the layer of still air on the inside and outside surfaces of all building elements which contribute an insulating effect and the bridging effects of components such wooden frames, which provide a path for increased conductivity.

The thermal transmittance (U) is a measure of how easily heat will move through a wall and is simply the reciprocal of the R-value.

The thermal lag is a measure of the difference between when the maximum outside temperature is reached compared to the maximum temperature inside. Offsetting the peak interior temperature to a cooler part of the day helps to provide a more uniform interior climate.

Table 1. Typical thermal properties of uninsulated wall types.

Table 2. Typical thermal properties of insulated wall types.