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Practical Solutions to Improve BASIX Thermal Comfort Rating

9 October 2017

Thermal Mass

The use of correct thermal mass can significantly reduce the heating and cooling loads of a dwelling. Thermal mass is a material’s ability to absorb, store and release heat energy. Heavy and dense materials such as masonry and concrete have the ability to absorb large amounts of heat energy, then release that heat at a slow rate. However, lightweight materials such as timber and metal cladding provide little thermal mass effects.

The thermal mass works by:

  • During winter, heat energy is stored during the day then released at night
  • During summer, materials are cooled during the night and heat at a slow rate throughout the day
  • Keeps the dwelling at a more consistent temperature by delaying heat flow, producing a warmer house at night in winter and a cooler house during the day in summer

The advantages of thermal mass include:

  • Lower annual heating and cooling loads
  • Reduces the need for high performance glazing
  • Can reduce insulation levels in walls and ceilings
  • Allows for a more flexible design, reducing the impacted of exposed and suspended surfaces

How to implement thermal mass:

  • The use of concrete slabs. Preferably concrete slab on ground to increase earth coupling benefits
  • Concrete intermediate floors
  • Concrete, cavity brick or reverse brick veneer external walls
  • Concrete or brick internal walls
  • Concrete roof
  • Allow direct contact with the winter sun
  • Leave materials bare by implementing polished concrete floors or exposed brick/concrete walls
  • Important to have good passive design, such as cross flow ventilation, to dissipate excess heat. This is important for high floors as heat will naturally rise.

House Passive Design

Passive design is the use of the environment to effectively heat and cool a dwelling. Well thought out passive design, along with thermal mass, can further reduce the heating and cooling loads of a dwelling.

Passive design consists of integrating key elements into the early design stages of a dwelling. Three of these key elements include floor layout, ventilation and shading.

Floor layout:

  • Important to avoid having zones detached from the main dwelling. This reduces the wall to floor ratio. Figure 1
  • Have zones connected to one another as much as possible. This minimises heat transfer from the external environment. Figure 2

Bedroom DetachedBedroom Attached

  • Bedrooms and night time areas on the top level or perimeter of the building
  • North facing living and dining areas to maximise natural sunlight


  • Ensure windows have large openability and placed at opposite ends of the dwelling to allow the removal of excess heat
  • Ensure good air flow paths to allow ventilation to pass through
  • Flowing open floor layouts, avoid the use of multiple small rooms


  • North facing windows to have correct horizontal shading to block the high summer sun, though allow the low winter sun.
  • East and west facing windows to have vertical shading or deep horizontal shading to reduce the effect of strong morning and evening sun glare
  • Adjustable shading and louvres that can be opened and closed at different times of the year

Nationwide House Energy Rating Scheme (NatHERS) software such as BERS pro and FirstRate5 will take all the above factors into account when simulating annual heating and cooling loads. Incorporating thermal mass and passive design into the early stages of design can significantly increase the star rating of a dwelling and ability to pass new stringent 2017 thermal heating and cooling caps.

For more information on thermal mass and passive design, or how BCA Energy can assist in meeting your BASIX requirements please contact Robert Romanous within our office on 1300 787 302 or at  if you wish to discuss this further.