Roof sarking is the flexible membrane laid over the rafters and under the battens of a tiled roof. It catches wind-driven rain and dust that get past the tiles, directs any water into the gutter, and, with a reflective foil face, cuts radiant heat into the roof space. On many new Melbourne roofs the building code requires it, and it is the first thing a roofer adds when a roof is re-battened.
The short answer
- Sarking sits under the battens and over the rafters
- It sheds water and dust that get past the tiles
- Foil-faced sarking also reflects radiant heat
- Low-pitch and long-rafter roofs must have it
- In Melbourne, check vapour permeance for condensation
What sarking does
Roof tiles shed most water, but not all of it. Strong wind can drive rain and fine dust up and between the laps, and a single cracked tile lets water straight through. Sarking is a second line of defence: it catches that water and carries it down the roof and out over the fascia into the gutter.
- Stops wind-driven rain and dust reaching the ceiling
- Gives a short-term buffer if a tile cracks or slips
- Reflective foil sarking reduces radiant heat into the roof space
- Reduces draughts through the roof space
When the building code requires it
The National Construction Code housing provisions (Part 7.3) set out when tiled roofs must be sarked:
| Roof pitch | Sarking required when |
|---|---|
| Under 18 degrees | Always |
| 18 to under 20 degrees | Rafter (top chord) length over 4,500 mm |
| 20 to under 22 degrees | Rafter length over 5,500 mm |
| 22 degrees and over | Rafter length over 6,000 mm |
The code also requires sarking to comply with AS 4200.1, sheets to be overlapped by at least 150 mm or taped, fixing at no more than 300 mm centres, and no sag greater than 40 mm. An anti-ponding device is needed where the pitch is under 20 degrees or there is no eaves overhang.
Condensation and vapour permeance
Melbourne sits in climate zone 6, where the code's condensation provisions apply to roof spaces. Part 10.8 requires a roof space in climate zones 6, 7 and 8 to be ventilated as set out in the code, or to sit immediately under the tiles of an unsarked roof, or above sarking with a vapour permeance of not less than 1.14 µg/N.s. In practice, if you are sarking a new roof, check the product data sheet for vapour permeance and ventilate the roof space as required. See our guide to whirlybirds and roof ventilation.
Types of sarking
- Reflective foil laminate: aluminium foil bonded to a reinforced fabric. Reflects radiant heat and sheds water.
- Heavy duty grades: thicker, more tear-resistant laminates that handle foot traffic and wind during installation better.
- Vapour-permeable membranes: designed to let water vapour escape while stopping liquid water, relevant to the condensation rules above.
We stock Rhino Heavy Duty and Rhino Extra Heavy Duty sarking, an aluminium foil and reinforced poly-woven laminate that sits under roofing to resist wind, rain and heat transfer. Check the product data sheet for the properties your job needs. See roofing materials.
Adding sarking to an existing roof
Sarking goes under the battens, so it cannot simply be slipped under existing tiles. Retrofitting means removing the tiles and battens on the section being sarked, laying the sarking, re-battening and relaying the tiles. That is why it is usually done during a re-roof, a re-batten, or when a section of roof is opened up for other work.
If you are lifting tiles anyway, it is the cheapest time to add sarking.
Installation basics
Walking on tiles cracks them and puts you at risk of a fall. WorkSafe Victoria treats falls from roofs as a serious hazard and puts edge protection ahead of ladders and harnesses. If you are not trained and equipped to work at height, use this guide to buy the right products and brief a roofer.
- Start at the eaves and run sheets horizontally across the rafters.
- Lap each sheet over the one below by at least 150 mm, or tape the joins, so water runs over the laps.
- Fix at no more than 300 mm centres with staples or as the manufacturer directs.
- Allow a slight drape between rafters but no sag over 40 mm.
- Run the bottom edge into the gutter so water drains away, with an anti-ponding device where required.
- Batten over the sarking and relay the tiles.
Pick up sarking, a staple gun, staples and battens from our Doveton and Mulgrave yards.
Common questions
What is sarking on a roof?
A flexible membrane laid over the rafters and under the battens of a tiled roof. It catches water and dust that get past the tiles and, if foil-faced, reflects radiant heat.
Is sarking required under roof tiles?
Under the NCC, tiled roofs under 18 degrees must be sarked, and steeper roofs must be sarked once rafter length exceeds set limits.
Can sarking be added to an existing roof?
Yes, but the tiles and battens must be lifted, because sarking goes under the battens. It is usually done during a re-roof or re-batten.
Does sarking cause condensation?
It can trap moisture if the roof space is not ventilated. In Melbourne, check the vapour permeance of the sarking and ventilate the roof space as the code requires.
How much should sarking overlap?
The NCC requires sheets to overlap by at least 150 mm or be taped, with fixings at no more than 300 mm centres.
Related
Sources: NCC 2022 Housing Provisions Part 7.3: Roof tiles and shingles; NCC 2022 Housing Provisions Part 10.8: Condensation management; WorkSafe Victoria: Prevention of falls in housing construction.
