What sarking does
Think of it as a raincoat under the roof. Monier, a major tile maker, says sarking can reflect up to 95% of the radiant heat coming off the roof, cuts the dust getting in, helps stop condensation staining and helps keep embers out. CSR Bradford, which makes sarking, calls it a protective second skin against burning embers in bushfire areas.
Bradford sorts sarking two ways: by how much heat it reflects, and by how well it lets water vapour pass through. Those two properties decide which type suits your climate.
When is it required under tiles?
Under the 2022 edition of the National Construction Code, every tiled roof pitched below 18 degrees needs sarking. Steeper roofs need it once the rafters run past 4,500 mm (18 to under 20 degrees), 5,500 mm (20 to under 22 degrees) or 6,000 mm (22 degrees and up).
The same code wants it to meet AS 4200.1, lapped at least 150 mm or taped, fixed at no more than 300 mm centres and sagging no more than 40 mm. Roofs under 20 degrees, or with no eaves overhang, also need an anti-ponding board along the eaves, so water running down the sarking can't pool behind the gutter.
Those figures come from the 2022 code. The 2025 edition was released on 1 May 2026 and each state is adopting it on its own timetable, so the rules where you live may now differ.
Foil or vapour permeable?
| Reflective foil laminate | Vapour permeable membrane | |
|---|---|---|
| Main job | Reflects radiant heat; under metal roofing it also acts as a vapour barrier | Lets water vapour escape from the roof space so it can dry out |
| Adds insulation? | Yes, when it faces a still air gap of at least 20 mm (Your Home) | No material R-value, says CSR Bradford |
| Climates CSR Bradford suggests | Hot humid and warm humid areas (non-permeable sarking) | Mild summer, very cold winter areas; also warm summer, cold winter areas with ceiling insulation above R4.1 |
| Watch out for | Foil conducts electricity, so it must not touch cables | It works alongside roof space ventilation, not instead of it |
Condensation in colder climates
Condensation forms when warm, moist air from the house meets the cold underside of the roof. In climate zones 6, 7 and 8, the 2022 code requires a ventilated gap of at least 20 mm above the insulation, and sarking that sits directly on the insulation must have a vapour permeance of at least 1.14 micrograms per newton-second. In plain terms, it has to breathe.
Raked or cathedral ceilings are trickier. Your Home recommends a vapour-permeable barrier with drainage battens, as thin as 20 mm, running up the rafters so condensation can drain and dry. If you're seeing drips on cold mornings, our guide on condensation or a leak helps you tell which.
Bushfire areas
For new homes in bushfire prone areas, Monier says tiled roofs need Roof Tile or Roof Tile Plus sarking and an anti-ponding board. For existing homes, an NSW RFS guide to upgrading recommends sarking with a flammability index of no more than 5 under the roofing whenever it's replaced. That guide is older and references AS 3959-2009, so check today's requirements for your Bushfire Attack Level with your council.
Adding sarking to an existing roof
Sarking sits under the battens on a tiled roof and under the sheets on a metal one, so adding it means lifting the roof covering. The sensible time is a re-roof, or when tiles come off for other work. On metal, Lysaght says foil should be draped 50 to 75 mm between supports, leaving an air gap that improves insulation.
How big a job it is depends on the roof area, the product (foil, permeable or fire-rated), whether the roof covering is coming off anyway, and whether an anti-ponding board or new battens are needed.
Questions about sarking
- Is sarking required for my pitch and rafter length?
- Which product and type are you using, and why for this climate?
- Will there be an anti-ponding board at the eaves?
- Is it rated for my Bushfire Attack Level?
- How will you keep foil away from wiring?
What you can check
You can
- Look through the manhole with a torch, without climbing in, to see if there's sarking under the tiles
- Note ceiling stains that appear on cold mornings rather than in rain
Leave to a roofer
- Lifting tiles or sheets to fit sarking
- Fitting anti-ponding boards and battens
- Any work near wiring in the roof space
What we'd insist on
If the tiles or sheets are coming off anyway, we'd have sarking put in, even where the code doesn't demand it, because adding it later means lifting the roof again. We'd choose the type for the climate rather than the price, and ask the roofer to explain why they picked foil or a breathable membrane for your area.
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.