Roof sarking and whirlybirds for coastal homes

Published 17 August 2026 · Updated 13 October 2026

What roof sarking does

Monier, a roof tile manufacturer, describes sarking as “a type of foil lining for your roof” and says it is “highly recommended for all roofing types.” It goes over the rafters and under the battens, so water blown in under tiles during a southerly runs down the sarking to the gutter instead of dripping onto the ceiling. It also keeps out dust and leaf litter, and the foil face reflects some of the sun’s heat.

Many older Beaches tile roofs were laid without it. You can tell from the roof space: if you look up and see the underside of the tiles and daylight at the laps, there’s no sarking. On those roofs a single cracked tile lets water straight onto the ceiling.

When tiles need sarking

Pitch decides it. Monier’s product pages for its Elabana concrete tile and Marseille terracotta tile both give a minimum pitch of 15° with sarking and 20° without. Its Elabana page says sarking is not mandatory above 20°, but Monier recommends it. A low-pitched extension or patio roof in tiles is the case to ask about.

Adding sarking to an existing roof

Sarking goes under the battens, so it can’t be slipped in from inside. On a tile roof the tiles and battens come off, the sarking goes on, and the tiles are re-laid. That’s why it’s usually done during a re-roof, or one section at a time where a roof keeps leaking. On a metal roof the sheets come off.

One Sydney contractor’s replacement page publishes this for doing a section:

Published price for re-laying a section with new sarking

One Sydney contractor’s roof replacement page, checked 1 October 2026. The page is undated and doesn’t say whether GST is included. Its Colorbond page says its “from $170” rate includes “removal of the old roof, new sarking, standard flashings and a corrugated profile”, with Klip-Lok or Trimdek profiles, two storeys and a pitch over 30° costing extra.

The same contractor’s re-roofing rates include “new sarking” in the price per square metre, which is one more reason to fold it into a roof replacement rather than pay for access twice.

Condensation under metal roofs

On a clear night a metal roof cools quickly, and warm, moist air from the house can condense on the underside of the sheets and drip onto the insulation and ceiling. It’s often mistaken for a leak because it shows up as drips with no rain.

The building code deals with this in the Housing Provisions, Part 10.8 (condensation management), which includes a clause on ventilating roof spaces with openings at the eaves and at or near the ridge. Fletcher Insulation’s technical bulletins say that clause applies only in climate zones 6, 7 and 8, so check with the roofer or building designer whether it applies to your house. The same bulletins describe vapour-permeable sarking for metal roofs, which lets moisture out rather than trapping it under the sheets. Ask which sarking the roofer plans to use, and why.

Whirlybirds: what they do and what suits the coast

A whirlybird is a wind-driven turbine over a hole in the roof. As it spins it draws hot, moist air out of the roof space, which helps with summer heat upstairs and with condensation. It works best with air coming in low down, at the eaves, to replace what goes out the top.

Check what it’s made of before one goes on a house near the surf. CSR Bradford’s WindMaster, for instance, has an aluminium turbine and flashing, a zinc-plated mild steel shaft and stainless steel and galvanised screws. The manufacturer lists it for tiled roofs from 15° to 45° and metal roofs from 3° to 45°. Salt attacks the steel parts and fixings first, and BlueScope’s coastal guidance on screws applies to them as it does to the rest of the roof (see steel roofs near the coast).

A rattling or wobbling whirlybird usually needs a new bearing or refixing, and a drip around its base is a flashing problem. Both are small roof repairs.

Sarking and vents on bush fire prone land

Parts of the Beaches border Ku-ring-gai Chase and Garigal national parks, and Northern Beaches Council’s bush fire prone land map covers many homes near the bush. On mapped land, sarking is a fire rule as well as a weather one. NSW’s Planning for Bush Fire Protection 2019 varies the national standard so that, for BAL-12.5 to BAL-40, any sarking used must “be non-combustible; or comply with AS/NZS 4200.1, be installed on the outside of the frame and have a flammability index of not more than 5 as determined by AS 1530.2”.

CSIRO’s best-practice guide adds a caution: “Do not assume that conventional sarking (even level 5 rated) is an ember or flame barrier in a combustible roof cavity.” For vents, Bradford sells a BAL version of its whirlybird “rated for use up to BAL 40 when installed to specification”. Your BAL certificate or bush fire consultant sets what applies to your house; the BAL roofing requirements checker summarises the NSW rules for each level.

Who can fit sarking and whirlybirds

In NSW the roof tiling licence covers sarking and battens, and both the roof tiling and roof plumbing licences include putting in skylights and ventilators. A contractor licence is needed for work valued at more than $5,000 in labour and materials, including GST. Check it on the Service NSW licence register.

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