It appears that the Australian Government is about to offer free ceiling insulation to thousands of homes. That fine when you want to keep the cool in with air conditioning or the warmth in with heating.
However, when the air temperature inside a house is much the same as the temperature outside, insulation of the ceiling is the wrong approach, particularly in sunny Queensland.
The best way to lower the temperature of the roof space above a ceiling is to ventilate it. Unfortunately most homes are badly designed and the roof space is sealed, trapping the hot air in. This hot air warms the ceiling warming of the air in the room below and producing a lot of radiant heat. Putting insulation above the ceiling does reduce the heat transfer during the day – and makes the roof space heat up even more. The room tends to be a bit cooler during the day – when we are at work. Unfortunately, the heated insulation takes a long time to cool down after the sun sets, and the room beneath it continues to be heated most of the evening – when we are more likely to be home.
If the roof space is well ventilated, then the temperature of the roof space approaches the ambient air temperature. When there is no temperature difference, then the insulation does nothing – it is not needed.
