You are getting quotes for a new roof, or maybe you have poked your head into the roof cavity to chase a draught, and someone mentions sarking. It gets said quickly, like everyone already knows what it means, and you nod along. So here is the plain version. Roof sarking is a thin, flexible membrane that sits under your roof tiles or metal sheets, and on most homes we look at on the Mornington Peninsula it does a lot more quiet work than people realise.
It is often the shiny, silvery-blue material you spot if you ever see a roof mid-build, rolled out in long strips before the tiles or sheets go on. Some people call it by a brand name like Sisalation. Same idea.
Think of it as a second skin under the roof
Your tiles or metal sheets are the first line of defence against the weather. They are not perfectly watertight on their own, though. Tiles overlap rather than seal, and wind can push rain sideways up and under them. Sarking sits below that outer layer as a backup. Anything that gets past the roof covering lands on the sarking and runs down it into the gutter, instead of dripping onto your ceiling.
It is laid over the rafters and battens, following the slope of the roof, so water always has somewhere to go. That is the whole trick, really. Give stray water a clean path out before it finds your plaster.
What sarking actually does up there
The water barrier is the headline job, but it earns its keep in a few other ways too, and they matter here on the peninsula.
- It handles wind-driven rain. We get plenty of it near the coast. A southerly change can drive rain almost horizontally, and that is exactly the kind of water that sneaks under tiles.
- It cuts condensation. When a cold night follows a warm day, the underside of a roof can sweat. On metal roofs especially, that moisture drips down. Sarking (or a thicker anti-condensation blanket) manages it before it becomes a damp problem.
- It reflects heat. Most sarking has a reflective foil face. Turned the right way it bounces radiant heat off in summer and helps hold warmth in winter, which takes some load off your insulation.
- It keeps dust and embers out. It blocks the fine grit and leaf litter that otherwise blows into the roof space. In bushfire-prone parts of the peninsula, the right sarking also helps stop burning embers getting in through gaps.
Does every roof around here have it?
No, and this one surprises people. A lot of the older tile roofs we inspect, particularly homes built a few decades back, were put on with no sarking at all. It simply was not standard practice at the time. Those roofs rely entirely on the tiles doing their job, which is fine until a tile cracks or a big blow pushes water where it should not go.
If you have an older home and you have ever had a mystery leak that the roofer struggled to pin down, a missing sarking layer is often part of the story. There is nothing catching the water once it is past the tiles, so it travels along a batten and shows up metres away from where it actually got in.
Do you actually need it?
For a new roof or a re-roof, sarking is usually a straightforward yes, and in many cases it is required. Whether it is mandatory comes down to the National Construction Code and factors like your wind rating and whether your address sits in a bushfire-prone area. Homes closer to the water, or up on the more exposed ridgelines, often fall into categories where it is expected. Your roofer or building surveyor can tell you exactly which rules apply to your block.
For a roof that is already on and behaving itself, it is more of a judgement call. If the roof is sound and dry, you do not need to rip it up just to slide sarking underneath. If you are already planning work, that changes the maths, which brings us to the question we get asked most.
Can you add sarking to a roof that is already on?
Not without lifting the covering, no. Because sarking sits underneath the tiles or sheets, the only way to fit it is to take that outer layer off, lay the membrane, and put the covering back. There is no quick spray or bolt-on version that does the same job from below.
In practice that means sarking gets added at one of two moments: when you are having the tiles lifted and re-bedded anyway, or during a full roof replacement. If either of those is already on your list, adding sarking at the same time costs far less than doing it as a standalone job, because the expensive part (getting the roof open) is happening regardless. When we quote a sarking installation on the Mornington Peninsula, we will always tell you honestly whether it is worth doing now or better bundled into future work.
Tiles or Colorbond, does it change things?
The principle is the same for both, but the emphasis shifts. Under tiles, sarking is mostly about catching wind-driven rain and stopping dust. Under metal, condensation control moves up the priority list, because sheet metal swings temperature fast and sweats more readily than tile. If you are still weighing up the two roof types, our Colorbond versus tile comparison walks through how each one behaves in our climate.
Whichever you have, the sarking needs to be set out properly, lapped the right way and drained into the gutter. Done well you never think about it again. Done poorly, or left out, and it tends to announce itself on the first really wet weekend.
If you are building, re-roofing, or just not sure whether your home has sarking at all, the simplest next step is to have someone actually look. We can check what is up there and tell you straight whether it is worth adding. Have a look at our sarking installation service or get in touch for a quote.
Common questions about roof sarking
Is sarking mandatory in Australia?
It depends on where you live and what you are building. The National Construction Code ties it to things like your wind region and whether the property is bushfire-prone, so many new builds and re-roofs need it while older homes were often built without. The safest answer is to check the rules that apply to your specific address before you start.
Do you need sarking under a tiled roof?
Tiles overlap rather than seal, so wind-driven rain can get under them. Sarking catches that water and channels it out to the gutter before it reaches your ceiling. It is strongly recommended, and on new tile roofs it is frequently required.
How much does sarking cost?
It varies with the size and pitch of your roof and how easy the roof is to access. It is far cheaper when done as part of a new roof or a re-lay than as a job on its own, because the roof is already open. We would rather come and look before giving you a figure than guess one that turns out wrong.
Is sarking waterproof?
Most reflective foil sarking is water-resistant rather than a fully waterproof membrane you would rely on by itself. It is a backup layer that manages the odd bit of water that gets past the tiles or sheets. It works with your roof covering, not instead of it.
Do Colorbond and other metal roofs need sarking?
Metal roofs heat up and cool down quickly, and that swing causes condensation on the underside. Sarking or an anti-condensation blanket manages that moisture so it does not drip into the roof space. Given the temperature swings we get near the coast, it is well worth having under a metal roof.
Can you put sarking on an existing roof?
Not without lifting the tiles or sheets, since it sits beneath them. That is why it is normally fitted during a re-lay or a full roof replacement rather than as a standalone retrofit. If you are planning either, it is the natural time to add it.
Does sarking go under or over the battens?
On a tile roof it is usually draped over the rafters and sits under the tile battens, so water runs down the membrane and into the gutter. Metal roof systems can differ. Your roofer sets it out to the manufacturer’s instructions so the laps and drainage are right.
