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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.

It’s a long term project, but my fiancee and I intend on building on our property one day. About a year and a half ago now we purchased just under ten acres in the Adelaide Hills, South Australia.

Currently we are considering our options to build. Looking at house plans, having our home designed by an architect, or trying to do it ourselves, there’s a lot of options just in there. Then we can go with a builder, get a kit home, or owner build (self build). After that there’s still a heap of other options within those choices… It’s never-ending!

We have always wanted an efficient home – a sustainable design, passive solar and passive cooling – the simplest way to create an efficient home. In Australia this starts with North facing windows, to allow the home to warm up during the winter, and strategically placed windows, doors and hallways in the house to allow cooling breezes to keep the home cool in the summer. I have quickly learned that this cannot be done properly by using a builder with set house plans. The design must suit the property.

So you’re left with either designing the home yourself, or if you’re not comfortable doing that, seeing an architect.

You also need to decide on what materials you would like your house made from. We are personally trying to build a green home, so we are choosing strawbale for the external walls. Strawbale houses are incredibly efficient, with very high insulation properties. Taken from “House of Bales“:

In winter, the sun and combustion heater keeps the house at a very comfortable temperature. In summer during 40+ degree heat waves the hottest the house got was 27 degrees.

Aside from the strawbales, we would like a concrete slab for thermal mass. This is a tough choice, as concrete production creates a large amount of carbon dioxide, however over time, a house built with concrete will save a lot of carbon dioxide production. To add to this thermal mass, we hope to use rammed earth walls within the design of the home too.

Then you have the smaller options along the way. These options can make big differences in the final comfort of the home. For example, using timber window frames can help keep the house warmer in winter. These should not be overlooked, as the price for a better solution is not often far from the price of the “standard” option.

Building an eco house takes time, lots of effort, and usually a huge amount of research on the owners’ behalf, but what more of a rewarding way could there be to build a house?