For maximum effectiveness, thermal mass should be insulated from external temperatures, i.e. it should be located within insulated walls. The benefits of thermal mass are considerably reduced if the external envelope is not insulated. For this reason brick veneer walls offer little thermal mass benefit, as the brick is on the outside of the insulated cavity.

Concrete Slab on Ground

A concrete floor slab directly on the ground will take advantage of the huge thermal mass of the earth beneath.

Inside North-Facing Rooms Using thermal mass in north-facing rooms should be a priority, particularly on those walls which receive direct winter sun. As the area of northfacing window increases, the more internal thermal mass is required to maintain a stable temperature

Hot Rooms During Summer Locate thermal mass throughout the dwelling for summer comfort, but particularly in north, east and west-facing rooms. Shading of the windows to these rooms is also important.

Amount of Thermal Mass

High levels of thermal mass are beneficial with the exception of alpine areas and some situations where solar access is poor. While technical studies often recommend certain percentages of thermal mass for different construction types and climate zones, in practice most homes have thermal mass provided in only the following few locations.

• Floor: concrete slab or timber floor.

• External walls: double brick/masonry or brick veneer/weatherboard cladding.

• Internal walls: masonry or stud walls.

Of all the material choices, the wall selection accounts for about 60"70% of the thermal mass of the building, with the floor area accounting for about 30"40%.

Generally, the more thermal mass the better. A double brick or masonry home on a concrete slab offers the highest comfort benefits and energy savings. However, the cost of heavyweight materials can outweigh the value of energy savings. For this reason, use as much thermal mass as you can afford to achieve comfortable indoor conditions.

In most cases, give first priority to provision of a concrete slab (substantially less cost than masonry walls) and supplement this with heavyweight walls where the building budget permits.