Is it worth adding ceiling insulation to an existing house?

In most Australian climates the ceiling is the largest single path for unwanted heat transfer, gaining heat from a roof cavity that can exceed sixty degrees in summer and losing it upward in winter. That is why insulating an under-insulated ceiling generally beats window upgrades on cost per unit of comfort gained.

Check these before it goes in

• Downlights. Non insulation contact rated fittings must be kept clear, and cutting gaps around twenty of them undoes much of the benefit. Changing them first is usually the better order of work.
• Wiring condition. Old, brittle cable buried under new batts is harder and more expensive to reach later.
• Existing insulation. Old batts that have compressed or slumped perform poorly, and topping up over them is often better value than removing them.
• Ventilation and moisture. Insulation over a bathroom or laundry exhaust that vents into the roof space rather than outside will make a damp problem worse.

The order that saves money

If you are doing downlights, wiring and insulation, do them in that order in one coordinated stretch. Every one of those jobs requires roof space access, and access is a meaningful share of what you pay for each of them separately.