Reverse Brick Veneer Research

Thermal Mass

Thermal mass is the ability of a material to absorb and store heat energy. A lot of heat energy is required to change the temperature of high density materials like concrete, bricks and tiles. They are therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass. Appropriate use of thermal mass throughout your home can make a big difference to comfort and heating and cooling bills by averaging out diurnal extremes.

Reverse Brick Veneer Vs. Traditional Brick Veneer

Reverse brick veneer construction is a preferred form of construction in areas with large diurnal temperature difference such as Melbourne. As bricks are considered a higher thermal mass than timber framing, it is therefore logical to place it inside the building not outside. In traditional brick veneer, the bricks are on the outside and they contribute very little to heating and cooling efficiency. Reverse brick veneer, however, provides a better solution. In winter, the bricks on the inside of a house can store the heat that is coming into the room (either from sunlight through windows, or from indoor heaters) and radiate it back into the room during the night. The insulation between the bricks and the timber framing stops the precious heat from escaping. In summer, keeping the windows and doors closed means that heat does not enter the home as easily, and the thermal mass acts to cool the interior. At night, any heat stored in the brickwork during the day can be easily dissipated through open windows.

Other Consideration:

To be effective, thermal mass must be integrated with sound passive design techniques. This means having appropriate areas of glazing facing appropriate directions with appropriate levels of shading, cross ventilation, and insulation.

Here is a diagram of a typical reverse brick veneer construction from the internet.

In the diagram, the layering is listed as below:

1. Interior lining: As a common brick veneer construction, this design provides a interior lining as wall finish.

2. Single brick wall: The brick wall in this design is non-load-bearing as it is in common brick veneer construction.

3. Cavity: This is one of the key elements of the insulation, the same as the gap in common brick walls.

4a. Timber framing: The timber framing is also a load-bearing structure.

4b. Insulation: Bulk wall insulation to insulate the thermal mass inside.

5. Insulation: Air-cell Permishield provides a layer of reflective insulation, helping to keep radiated heat off the inside layers.

6. Batten: The reflective insulation only works when there’s an air gap, which is created via battens nailed through to the timber frame.

7. Fire-protecting Gyprock: Additional layer to meet the required fire-rating.

8. Sarking: Building wrap to seal up the building envelop.

9. Weatherboard: The exterior cladding to provide the desired finish surface.

Diagram 03. Example of Reverse Brick Veneer Construction

The example above provides a good example for our group to study and a baseline to make our own design. There are a few things we need to consider for this project:

1. Layer 1 of the example design, the interior finish, is rather a bad idea as traditional finish materials have low thermal mass. The covering of the brick wall reduces or even cancels the heat storing capacity of the bricks and defeats the purpose of placing the brick wall internally. Therefore for our project, we will not put up any internal lining and let the bricks exposed.

2. The whole wall needs to be sealed top and bottom to protect it from undesired exterior weather condition as any other construction methods. We are currently thinking about having a roof (corrugated roof sheet or tray deck roof to be decided later).

3. Layer 5 reflective insulation and Layer 7 fire-protecting Gyprock are specifically designed for this particular case for certain requirements. However, it may be unnecessary for every single construction. As we are only building a standard reverse brick veneer, we will not have these two layers.

Thermal Lag

Thermal lag is the rate at which heat is absorbed and re-released by uninsulated material. Lag is dependent on conductivity, thickness, insulation levels and temperature differences either side of the wall. Consideration of lag times is important when designing thermal mass. The table below indicates the lag times for common materials.

Table 06. Thermal Lag of Common Building Materials

Thermal lag influences internal−external heat flow through walls, especially in cool and cold climates, such as what we have in Melbourne, where lag times are reduced by increased internal-external temperature differences. From the table we can easily see that adobe, rammed earth and compressed earth blocks provide considerably longer time lag, they are not suitable for our wall, however. On the other hand, autoclaved aerated concrete can provide a marginally longer time lag than double bricks and concrete with less material thickness. As our group have selected Hebel, an autoclaved aerated concrete product, as our building material, we will use it as a substitute for traditional bricks to build our reverse brick veneer wall.