thermal mass


As with all design decisions it is important to consider the context, the application and the lifecycle. Both Phase Change Material and Thermal Mass have their own advantages.

Thermal mass has been around since the first creature crawled out of the sea to sun itself on a rock. It comes in many shapes and forms, the most common ones would be the traditional clay brick or in-situ concrete. However any material that is heavy/dense can be utilised as thermal mass even water! At EME we often choose to use lower embodied energy thermal mass in the form of rammed earth or superadobe.

Phase change material is not massive and comes in manufactured sheets that are installed within the fabric of the building. One advantage of phase change is that it is lighter in weight and therefore can be integrated into a retrofit situation without upgrading the structure and multi-storey buildings. Unlike thermal mass construction, phase change does not have the poetry and material sensibility that thermal mass offers. Phase change is generally concealed within a wall.

Wrights Terrace rendered brick walls for thermal mass

Both methods work on the principle of storing energy over a period of time and releasing it later, you can think of it as a rechargeable battery. In winter a rammed earth wall carefully positioned to capture the direct sunlight, will absorb the sun’s energy in the form of heat. When the sun goes down and the temperature drops the wall gives back the heat to the rooms, providing a comfortable environment. Thermal mass can store energy and stabilise temperatures without direct exposure sun, taking the edge off fluctuations in temperature outside. It slows down the rate of temperature change, similar to the effect the ocean has on coastal climates. It is still very important to carefully integrate any thermal mass or phase change to avoid thermal bridging and other effects that can handicap the benefits.

Phase change is slightly different in the way it absorbs and transfers energy and in fact has been widely used as an alternative to insulation, the theory being that the phase change material can absorb the warmth of the building during the day and prevent the cold coming in at night by changing from liquid to solid. From my point of view phase change material is too expensive to be used in place of conventional insulation and provides far better bang for buck being utilised as an internal thermal wall storage system.

This is just a very brief introduction, contact us if you’d like to discuss this more.


Here are a few interesting points to consider:

– Phase change is not made in Australia so it has more travel miles

– It is made from by-products of the soy, palm coconut manufacturing process laminated between plastic sheets; it is likely to be lower embodied energy than the common brick

– They are developing a PCM made from algae

– Thermal mass walls can be structural; PCM needs a wall to be installed

– PCM lighter

-Thermal mass has an aesthetic beauty

thermal mass rammed earth
River house systems, underground cooling labyrinth of ducts bring cool air in off the river and into the house
Monitoring of indoor and outdoor temperatures at the river house
Energyplus rammed earth analysis showing moderating effect of the thermal mass on internal temperatures
Mildura Eco Living Centre earthbag superadobe wall summer mode
winter mode
Phase change wall at the Warragul house
Phase change material House Design
Phase Change House plan showing internal phase change wall
Biopcm phase change material made from soy and palm biproducts

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