Insulation reduces the rate of heat flow between inside and outside. Heat flows when the outside temperature is hotter than the inside, like on a hot summer day. Heat flows outward when the inside temperature is hotter than the outside, like in winter or at night.

There are two main types of insulation:

  • Bulk insulation acts primarily by reducing heat transfer by conduction and convection. Use bulk insulation at ceiling-level, in walls and floors.
  • Reflective insulation acts primarily by reducing heat transfer by radiation. Use reflective insulation at roof-level and in walls, especially in hot climates.

To lower summer heat gains through the roof, also consider:

R‑Value: thermal resistance

The effectiveness of insulation is related to its thermal resistance, called R‑Value, and is measured in m².K/W.

The Total R‑Value of a composite building element is the sum of:

  • the System R‑Value of construction, which includes:
    • the Inherent R‑Value of the construction materials; and
    • the resistances of any airspaces (considering reflective surfaces); and
  • the surface resistances, which includes:
    • indoor and outdoor air films; and
    • for floors, the ground surface resistance; and
  • any Additional R‑Value provided by bulk insulation materials.

Note that the performance of reflective insulation products is typically stated as a Total R‑Value or System R‑Value because these products require the adjacent airspace(s) to perform as tested.

Direction of heat flow

This is the required direction of heat flow in which the R‑value must be achieved. The direction is dependent on the climate zone.

In summer heat flows down through the roof and up through suspended floors whereas in winter it flows up through the roof and down through suspended floors.

Foil insulation products installed in floors, ceilings and roofs have significantly higher R‑values for heat flowing down than up. BASIX provides the direction of heat flow so you can select the best insulation for your climate. For walls the R‑value is the same in summer and winter because the heat is flowing horizontally.

Bulk insulation products can also be used because they will meet the required R‑value in both directions.

Check the manufacturer’s product information for the direction of heat flow. Some manufacturers might show summer and winter R‑values on their product literature. They will be able to clarify the direction of heat flow for these values for roofs and floors.

Condensation in buildings

Condensation, in relation to buildings, is the process of water vapour in moist air changing to liquid form when it comes into contact with cold surfaces (surface condensation) or is cooled while permeating the building fabric (interstitial condensation). Surface condensation forms visible droplets of condensate. Interstitial condensation releases the moisture in permeable materials such as bulk insulation, timber and masonry.

The ABCB has produced the "Condensation in Buildings" information handbook to explain the design strategies available to minimise the risk of condensation. The handbook is available on the Australian Building Codes Board (ABCB) website.

See also: