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In layman’s terms, thermal mass is when a body of mass has an ability to store heat. Why am I writing about this? Well it’s hugely beneficial to build a house with a high amount of thermal mass.

Thermal mass helps a house to be comfortable – it regulates temperature. This is very helpful in climates where the temperature is hot during the day but cold during the night. Thermal mass also helps to minimise the amount of man made energy used to heat and cool a house.

Australia is very slow in the uptake of using thermal mass effectively. While many of our houses built are brick veneer on a concrete slab, most of our windows are located in the wrong places, and often walls and windows aren’t shaded properly during the warmer months. We end up with hot houses in the summer, and cold houses in the winter.

An interior wall made from rammed earth.

Building with quality materials and a good design means costs saved on thermal insulation and other materials during the building process, but also heating and cooling further down the track.

Common sources of thermal mass include water, bricks, earth (mud-brick, earthen render, etc), rocks/stones, rammed earth and concrete.

I have mentioned in the past that we would like to build with a concrete slab for the benefits of thermal mass. We also intend on building with two rammed earth walls, internal to the house with adequate windows to heat these walls during the summer, and blinds to shade the walls in the winter.

Rammed earth has a very high density, and as a result is a perfect material to use for thermal mass. Not only is it very effective in keeping a home warm in the winter and regulating heat in the summer, it looks great!

What is rammed earth made from? It is as it sounds really – a soil mix that is compacted. The mix is balanced between clay, sand and aggregate. The mix can change to suit the look that the builder is going for, sometimes with marbled effects throughout the wall. Some rammed earth builders add cement, but not all. Walls are compacted in layers usually around 15cm high.

To me, it’s just another example of how some “out of the box” thinking can make your home a lot more comfortable, and a lot cheaper to live in for the long haul, not to mention adding some unique, earthy design features that aren’t seen that often.