When selecting building materials, the main consideration should be their thermal mass. This refers to a heavyweight materials ability to store thermal (heat) energy.

Using materials with thermal mass in the floor or walls of a building enables those elements in the structure to:

• absorb heat from the sun during winter days and release that heat back into the living spaces at night or during cooler periods, producing more comfortable temperatures; and
• absorb heat from the building during hot summer days, having been cooled down via natural ventilation during the previous cooler evening i.e. provide natural air conditioning.

On the other hand, lightweight materials (such as timber or plasterboard), used internally, allow rooms to heat up and cool down quickly. This is useful in rooms which require occasional heating, or if you live in a tropical climate and cool your home by opening doors and windows.

Where external walls are lightweight and insulated, providing mass in internal walls minimises the daily temperature fluctuations and improves comfort considerably.

The floor is commonly the most economical place to locate heavy thermal mass materials (eg. concrete slab) and its thermal performance will be best in north facing rooms receiving direct sunlight.

Hard floor finishes are preferable because they thermally connect the air mass in the dwellings to the thermal mass in the earth below.

Consider your climate

Climate and geographical location will influence your choice of building materials and your building design.