What does an R-value actually mean?
R-value measures how well a product resists heat flow, and higher is better. Your Home, the Australian Government's guide to sustainable houses, says the number that counts is the Total R-value: every layer of the roof and ceiling added together, including air gaps.
Two things trip people up. Roofs with reflective foil get an 'up' figure for winter and a 'down' figure for summer, and you should look at both. And Australian R-values aren't comparable with American ones, which look much higher, so ignore overseas numbers.
Insulation sold here must meet AS/NZS 4859, and reflective insulation must meet AS 4200.1. A decent quote names the product and its labelled R-value.
Which type does what?
| Ceiling batts | Reflective foil or sarking | Blanket under metal roofing | |
|---|---|---|---|
| How it works | Bulk insulation that slows heat moving through the ceiling | A shiny surface that reflects radiant heat | Bulk insulation with a foil face, laid right under the sheets |
| When it goes in | Any time there's access to the roof space | Usually when a roof is built or replaced | When a metal roof is laid or replaced |
| What it needs to work | No squashing and no gaps | A still air gap of at least 20 mm beside the shiny side | Held hard against the sheets, with ceiling insulation as well |
| Extra benefit | Easy to top up later | As sarking, it helps keep dust and embers out | Cuts rain noise on steel |
| Watch out for | Clearances around downlights and flues | It conducts electricity, so it must not touch wiring | It only goes in while the roof sheets are off |
What does the building code ask for?
For new work, the 2022 edition of the National Construction Code sets minimum ceiling insulation by climate zone. For a pitched roof with a flat ceiling, a standard roof, no reflective insulation and little insulation under the roof, the figures include R3.5 in climate zone 4, R3.0 in zone 5 and R4.0 in zone 6.
In the warmer zones, darker roofs need more. Zone 2 runs from R3.0 to R4.0 depending on roof colour, and zone 3 from R3.5 to R5.0. In the coldest zones it flips: zone 7 runs from R3.5 to R5.0 and zone 8 from R3.0 to R4.5, with lighter roofs needing the higher figure.
These are minimums for new building work. The Australian Building Codes Board says existing homes don't have to meet the current code unless new building work is done. NCC 2025 was published on 1 May 2026 and each state adopts it on its own date, so ask your installer which edition applies. Your council or installer can also tell you your climate zone.
Where do roof colour and ventilation come in?
A darker roof soaks up more of the sun's heat, which is why the code asks for more ceiling insulation under dark roofs in warm zones. Our Colorbond vs tile guide covers how colour affects heat.
Roof spaces get very hot. CSR Bradford says they can reach 70 degrees C in summer without ventilation, and vents help clear heat and the moist air that leads to condensation. In climate zones 6 to 8, the 2022 code requires a ventilated space of at least 20 mm above the insulation, or vapour permeable sarking, to manage condensation. Our roof ventilation page explains the vent options.
Electrics and asbestos come first
Your Home says the Australian Standard AS 3999 requires an electrical safety check by a licensed electrician before insulation goes into an existing home. Foil insulation conducts electricity, so it must never touch cables or equipment. Insulation also needs clearance from flues and older halogen downlights, and Your Home suggests replacing those with IC-4 rated LEDs. Some older homes used loose-fill asbestos as ceiling insulation. If there's loose, fluffy fill in the roof space of a pre-1990 house, leave it alone and call a licensed asbestos assessor.
How to pick the right insulation
Find your climate zone
Your council or an insulation installer can tell you which NCC climate zone you're in.
See what's there now
From the manhole, with a torch, look at what's on the ceiling and how deep it is. Don't crawl in if the wiring looks old, the space is very hot, or there's loose fluffy fill.
Book the electrical check
A licensed electrician does the AS 3999 safety check before anything new goes in.
Choose the R-value
Treat the code figure for your zone as the floor. Higher values resist more heat, but only if the batts are fitted without gaps and without being squashed.
Match the type to the roof
Ceiling batts suit almost any house with a roof space. If you're re-roofing in steel, add a foil-faced blanket under the sheets. BlueScope says that, plus ceiling insulation, gives the best thermal result under metal.
Check the quote
It should name the product, the labelled R-value, the area covered, and how clearances around lights and flues will be handled.
What you can do, and what needs a professional
You can
- Find out your climate zone
- Look in from the manhole with a torch
- Work out the ceiling area roughly from a floor plan
- Book the electrician's safety check
- Ask installers to name the R-value and the standard
Leave to a roofer
- The AS 3999 electrical safety check, by a licensed electrician
- Fitting foil anywhere near wiring
- Blanket and sarking under a new roof, by a roofer
- Anything involving suspected loose-fill asbestos, by a licensed assessor
Where we'd spend first
If your ceiling insulation is thin, patchy or missing, that's where we'd put the money first: batts at or above the code figure for your zone, fitted with no gaps, after the electrician's check. If a metal roof is coming off anyway, we'd add a foil-faced blanket under the new sheets while the roof is open, because that's the one time it's easy. We wouldn't pay extra for a big R-value number unless the installer can show how they'll keep it gap-free.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.