Roof insulation and thermal performance basics
How heat moves through a roof in Queensland, the difference between sarking, insulation blankets and ceiling batts, and how to reduce heat, noise and condensation.
By Top Tin Roofing · Updated 19 October 2026 · 2 min read
How comfortable your home feels in a Queensland summer has a lot to do with the roof. The roof takes the full force of the sun, and how it handles that heat makes a big difference upstairs. Here are the basics.
How heat moves through a roof
The sun heats the roof surface. That heat then moves:
- Down through the roof sheets into the roof space
- Through the roof space, which can get very hot in summer
- Through the ceiling into your rooms
Each layer you add slows the heat down at a different point.
The three main layers
Roof colour
A lighter roof colour reflects more of the sun's heat, so less heat enters in the first place. See our guide to choosing a Colorbond colour for Queensland heat.
Sarking or an insulation blanket under the sheets
Sarking is a reflective layer laid under the roof sheets. An insulation blanket is a thicker layer, often with a reflective face, that adds insulation. Both sit directly under the sheets and:
- Slow heat moving from the sheets into the roof space
- Reduce rain noise on a metal roof
- Help control condensation on the underside of the sheets
The easiest time to add one is during a roof replacement, while the old roof is off.
Ceiling insulation
Batts or other insulation on top of the ceiling slow heat moving from the roof space into the rooms below. If your ceiling insulation is old, thin or patchy, topping it up can make a noticeable difference.
Ventilation
A hot roof space keeps pushing heat down into the house. Ventilation lets some of that hot air escape. Common options include whirlybirds and other roof vents. Ventilation works well together with insulation, not instead of it.
Condensation on metal roofs
On cool nights, the underside of metal sheets can get colder than the air in the roof space. Moisture in that air condenses on the sheets and can drip, which people sometimes mistake for a leak. The usual fixes are:
- A blanket or sarking under the sheets
- Good roof space ventilation
- Reducing moisture coming up from the house, for example from unvented bathrooms
Noise
Rain on a metal roof is louder than rain on tile, especially with nothing underneath. An insulation blanket under the sheets reduces that noise a lot. If noise is a concern, mention it at the quote.
Putting it together
| Layer | Main job | When to add it |
|---|---|---|
| Lighter roof colour | Reflects heat | When choosing the new roof |
| Sarking or blanket | Slows heat, reduces noise and condensation | During roof replacement |
| Ceiling insulation | Slows heat into rooms | Any time, from inside the roof space |
| Ventilation | Lets hot air escape | During or after replacement |
Ask during your quote
When we quote a new roof, we explain the options for sarking and insulation blankets and how they suit your home. You choose what goes in, and it is set out in the written quote.
Questions
Do I need both a roof blanket and ceiling batts?
They do different jobs. A blanket under the roof sheets slows heat entering the roof space and reduces rain noise. Ceiling batts slow heat moving from the roof space into your rooms. Many homes benefit from both.
Why does my metal roof drip on the inside?
That is often condensation, when warm moist air meets the cold underside of the sheets. A blanket or sarking under the sheets and good roof space ventilation usually help.
Written by the team at Top Tin Roofing, a Brisbane roofing business replacing roofs and installing Colorbond. QBCC licence 15587145.
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