Thermal mass describes the property of a substance where it absorbs heat from the environment. Heavyweight building materials such as concrete and bricks have a high thermal mass with concrete having the highest ability to absorb heat.

In the days before air-conditioning, the best place to be in summer was on the concrete floor under the kitchen table. The temperature-lag effect is directly related to the thermal mass of that material.

Building insulation is an important part of effectively using thermal mass. Concrete absorbs solar radiation for a short period until it reaches a point when it will transmit the heat inside the building. Similarly in winter, the cold (low energy) outside of the concrete will ‘suck out’ the heat energy from the inside.

The Australian way of insulating is inefficient as the typical technique involves building with concrete or bricks on the outside and insulating the inside. This completely nullifies and wastes the effect of thermal mass, especially in winter when a heavy, cold mass draws out heat from the inside to warm up the outside.

All around the rest of the world, buildings are insulated from the outside, and the mass of the building is part of the interior insulated envelope. In summer, there is a heat sink for any energy entering through the ‘weak spots’ in the envelope, usually the windows. Very little heat transfers through the insulation if it is done correctly with no thermal bridging.

Over the course of a 38-degree day, the temperature will increase by around 5 degrees. With a bit of smart management, opening the windows when the evening breeze sets in, will allow heat energy out of the building and reset the ability of the mass to absorb the heat of the following day. Of course, towards the end of an Australian summer, ambient temperatures rise and stay hot for days on end – but a high thermal mass building will still be more comfortable.

In winter, good planning will have the winter sun shine in the windows and allow the interior mass to heat up. Space heating will also transfer heat into the mass. At night when the ambient temperature drops, the mass will radiate the heat back into the room keeping it comfortable and warm.

The intelligent use of a high-thermal mass building system such as THERMOMASS will drastically reduce the energy use of the building. 

Composite Global Solutions can assist with effectively utilising thermal mass in a new building.