Thanks to the climate crisis, Brisbane’s average summer maximum temperature is predicted to rise to over 30°C by 2030 and to over 32°C by 2070. By 2030, Brisbane’s climate will be closer to the current climate of Bundaberg, about 300 kilometres north. By 2050, Brisbane will experience an additional two to eight days per year with temperatures over 35°C. At that time our climate is anticipated to be more like the town of Mareeba in Far North Queensland, 1,400km north.

It’s going to get hotter in Brisbane, and if our homes aren’t suitably built and designed, we are going to suffer during the coming heatwaves. And it’s not just the heat we need to worry about. Per capita, there are double the rate of cold-associated deaths in Australia as there is in Sweden. Given the stark differences in climate between the countries, it’s hard to imagine how this is possible. One reason that’s been identified as a contributing factor is the poor build quality of our homes, mockingly referred to as glorified tents.

My first article introduced the importance of energy efficiency, and how retrofitting our homes can make them healthier and more comfortable. Retrofitting your home with insulation, or replacing damaged or inefficient insulation, is one of the best ways to improve energy efficiency. That’s because we are limiting the number of times we need to rely on air-conditioners or heaters, saving energy and money. Insulation comes in many forms, but essentially, it’s a material that slows down or prevents the flow of heat. Insulation helps to keep a building cooler in summer and warmer in winter, resulting in healthier, more comfortable homes.

Insulation options for my 1920’s Queenslander include the sub-floor, ceiling, and the internal and external walls. As a guide, roughly 40 per cent of heat loss in the home is through the ceiling, 24pc through the walls, and 10pc through the floor. Before we take a look at each of these options, let me briefly explain the important concept of an R-value. Insulation levels are measured in R-values, which calculate the thermal resistance (resistance to heat flow) of a material, and minimum requirements under the Building Code of Australia (BCA) vary depending on climate. The higher the R-value, the higher the level of insulation. Brisbane homes must have ceiling insulation with a minimum R-value of 4.1.


Ceiling insulation is a common energy efficiency retrofit solution for residential homes. Research has shown how insulation is crucial to reducing the amount of heat penetrating through the roof and ceiling and entering a home. The ceiling and roof area of my home have been insulated. The ceiling insulation is loose fill rockwool and the roof section is insulated by glass wool batts with a heat reflective foil layer, to an R-value of 3.0. After a dusty crawl around inside the roof, I wasn’t able to work out when this installation was completed. Judging by the look of it (see photo below), it wasn’t done recently…

The shabby state of the insulation in my roof

Since my roof and ceiling are insulated to an R-value of 3.0, below the minimum requirement under the BCA, I need an upgrade to meet only the minimum standard. Given the deteriorated condition of the insulation, it makes sense to replace both the roof and ceiling insulation and upgrade to an R-value of at least 4.1. Doing so gives an immediate reduction to summer heat gain and winter heat loss.

Internal and external walls

The internal and external walls of my home are constructed of timber and are uninsulated. Timber has low thermal mass and does not retain heat. In a Queenslander home, heat is absorbed into and through the timber walls on hot days, which can make the home uncomfortably warm. On a cooler day, the desperately sought-after warm air inside the home escapes and has us reaching for the jumper or switching on the heater. Installing wall insulation would help. Due to the construction style, internal wall insulation isn’t possible because the internal walls do not have wall cavities – there’s no space between room dividing walls for insulation to be added. The only option is to retrofit external wall insulation. In a Queenslander home this means the external timber cladding needs to be removed, insulation installed, and the cladding replaced. Doing this will improve the thermal comfort and energy efficiency of the home and is worth pursuing. The wall insulation must be no less than the minimum R-value for Brisbane of 2.8.


Renovations of Queenslanders, particularly in recent times, have seen the homes restumped and raised to a level that allows a second storey to be built underneath. This isn’t the case for my home, and the uninsulated sub-floor is still accessible. While sub-floor insulation for raised timber floors can be useful in cold climates where heat escapes through the floor, it is less practical in sub-tropical climates. On a hot Brisbane day, the temperature in the sub-floor area is cooler than the indoor temperature of the home. Installing sub-floor insulation will result in less cool air entering the home, meaning we will be more likely to run fans or an air-conditioner to stay cool. While energy efficiency gains would be possible when weather is cool (July to September), any energy savings would be overshadowed by the extra heat gain throughout the rest of the year. Based on this, I’ve decided not to install sub-floor insulation.

To insulate my home is expected to cost upwards of $5000. Insulation costs will vary from home to home depending on the choice of insulation material and the size of the home. This represents a significant up-front cost barrier for many homeowners. That being said, insulation is a tried and tested method for maintaining a comfortable temperature in the home. This makes it an attractive retrofit option and helps to alleviate some of the concern over what is a sizeable financial outlay.

Like many energy efficiency solutions, adding insulation to your home will involve a considerable investment up-front, but it will also reduce your energy bills by between 20 and 50pc, leaving you better off in the long-run. At the very least, you’ll be left with a well-insulated tent.

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