Roof sarking is one of those things you never see once your home is finished, and one of the first things to get cut from a quote. Here's what it does, when you need it, and why I don't think it should be optional.

What is roof sarking?

Roof sarking is a pliable membrane laid under your roof tiles or sheets. Its main job is to catch any water that gets past the roof covering, from wind-driven rain, a cracked tile or a blocked valley, and drain it to the gutter. Some sarking also has a reflective face that cuts radiant heat.

It's installed over the rafters or trusses before the battens, running horizontally across the roof with overlapping laps so water runs down and out into the gutter.

Sarking isn't insulation. On its own it adds very little R-value. Your ceiling insulation does the heavy lifting. Reflective sarking can improve thermal performance, but only when its reflective face sits next to an air gap. Pressed hard against something else, the reflective benefit largely disappears.

C9 - Tile Roof, Box Gutter and Flashing Inspection Checklist

$59.00 AUD

Last updated 5 Oct 2026 · Revision 1 · Free updates for life

Checklist Type: Minor

Form Factor: Fillable, print-ready PDF (A4, 23 pages)

When to use: Roofing stage (tile roof), before the linings go in

A 177-point checklist for tiled roofs. Check tiles, sarking, battens, ridges, gutters, box gutters and flashings before the linings go in, when problems are easier to fix.

Preview C9

See all our checklists

Buy C9 – $59

What it does for your home

  • Catches leaks: tiles in particular aren't watertight in storms. Sarking is your second line of defence.
  • Keeps out dust and embers: it helps stop dust, debris and, on bushfire-prone sites, embers getting into the roof space.
  • Cuts radiant heat: reflective sarking with an air gap reduces the heat radiating from a hot roof into the roof space. Useful in a Queensland summer.
  • Manages condensation: the right membrane lets moisture escape from the roof space instead of trapping it, which reduces the risk of mould and rot.

The main types

Sarking materials in Australia are covered by AS/NZS 4200.1 (materials) and AS/NZS 4200.2 (installation). Membranes are rated for how well they resist water and how much water vapour they let through.

  • Reflective foil sarking: a foil laminate that reflects radiant heat. Common under tiles in warm climates.
  • Vapour-permeable (breathable) membranes: block liquid water but let water vapour escape, which helps prevent condensation in the roof space.
  • Combination products: reflective and vapour-permeable in one.
  • Insulation blankets with a foil facing: used under metal roofs. The blanket provides insulation and reduces condensation and rain noise, while the foil face acts as the membrane.

Which one suits your roof depends on your climate, the roof covering and ventilation. NCC 2022 condensation rules affect which membrane class suits your roof, especially in cooler climates, so the choice should be specified in your plans, not left to whatever's on the truck.

When is sarking required?

It depends on the roof:

  • Tiled roofs: the tile installation standard (AS 2050) and tile manufacturers require sarking in some situations, typically lower roof pitches and higher wind classifications. Check the tile manufacturer's installation guide for your pitch and wind rating.
  • Bushfire-prone sites: depending on your bushfire attack level (BAL), AS 3959 sets requirements for sarking under tiled roofs.
  • Metal roofs: sarking or a foil-faced blanket is commonly used to manage condensation, heat and noise. Check the roofing manufacturer's guidance.

Even where it isn't strictly required, roofing manufacturers generally recommend it.

What to check on your build

  • Is sarking (or a blanket) shown in your specification, with the product named?
  • Is it continuous, with the laps running the right way (upper sheet over lower) so water drains to the gutter?
  • Does it drape slightly between rafters so water can run under the battens?
  • Is it dressed into the gutter at the eaves, not stopping short where water can drip into the eave lining?
  • Are tears and holes repaired before the roof goes on?

Our C9 Tile Roof checklist (above) and the C8 Metal Roof checklist walk you through the roof inspection.

Why sarking shouldn't be an optional extra

CSR Roofing strongly recommends sarking or underlay on all roofing projects. You might think, "Of course they do, it sells more product." But roofing manufacturers have done extensive building science research and play a big part in developing Australian Standards alongside industry groups. When you read their installation manuals, they're clear about the minimum each home needs.

Unfortunately, many builders treat essential items like sarking as optional extras or upgrades. That shouldn't be the case. Your new home should be built to stand up to its environment: resisting water, moisture and mould, and staying comfortable without leaning hard on the air conditioner. Leaving out sarking to make a price look cheaper is a disservice to homeowners.

If it's not in your quote, ask why, and ask what it costs to add. It's far cheaper now than after the roof is on.