Thermal Mass

The thermal mass provided by bricks absorbs and gives off heat slowly after many hours; the more brick there is in a wall the more heat that can be absorbed. Two leaves of brick or cavity brick offers high thermal mass, and meets the BCA heavy mass requirement allowing a significantly lower level of added insulation. One leaf of brick and brick veneer provides medium thermal mass and is not eligible for the lower insulation concession under the code.

University of Newcastle researchers tested four building types (insulated brick veneer, reverse brick veneer, insulated lightweight and insulated cavity brick) for their heating and cooling demands. The results showed that the insulated cavity brick example performed the best.

The research also cast doubts on two long-accepted truths about energy efficient building design. Firstly, researchers found there was no correlation between the R-Value of a wall and energy usage, and, secondly, R-Value was not the sole predictor of thermal performance.

When compared to insulated cavity brick construction, an insulated lightweight building with higher thermal resistance but no thermal mass had more than twice the daily temperature swing during hot conditions.


Figure 1 External and internal air temperatures for lightweight and insulated cavity brick modules, January 2006 (University of Newcastle)

The university researchers found there was an immediate flow of heat from the external surfaces of the insulated lightweight building into the room through the walling system as no thermal mass was present to produce a thermal lag. Brick veneer constructions behaved similarly but with a reduced and delayed effect due to the thermal lag of the exterior skin.

As a result, the insulated lightweight building was typically the first to activate either heating or cooling due to the rapid response to driving conditions. And the energy consumption in the lightweight building was found to be higher as climate control systems worked harder to counter the large daily temperature swing.

When tested with air conditioning in the various test buildings, the insulated cavity brick house always used less power to maintain the internal temperature within a specified range, compared with other building types. It was shown that thermal mass with insulation in the cavity works best, with researchers highlighting the fact that the internal thermal mass combined with the cavity insulation aided the system in reducing energy consumption.

Figure 2 Combined Total Energy Consumption – all seasons (University of Newcastle) CB: Cavity Brick; InsCB: Insulated Cavity Brick; InsBV: Insulated Brick Veneer; InsRBV: Insulated Reverse Brick Veneer