Roof Sarking
Roof sarking might not be the most glamorous part of a roofing project, but it’s one of the most important. Installed beneath the tiles or metal sheeting and above the rafters, sarking is the hidden layer that provides a secondary line of defence against water infiltration, improves the thermal performance of the roof, and helps manage moisture in the roof space. In the climate of Coffs Harbour — hot, humid summers, significant annual rainfall, and a coastal environment — sarking provides measurable, real-world benefits that make it worth including in any new roof installation or major re-roof project. At Roof Restoration Coffs Harbour, Nathan Locke installs sarking on all new tile roof projects as a matter of course, and he can advise you on the right sarking specification for your specific roof and situation.
What Is Roof Sarking?
Roof sarking is a flexible sheet material — typically a foil laminate or a non-woven polymer membrane — installed under the roof tiles or metal sheeting but above the roof battens and rafters. It drapes or sits between the rafters, spanning across the full underside of the roof before the battens are fixed.
The term “sarking” covers several product types with different properties:
Reflective Foil Sarking
The most common type of residential sarking in Australia, reflective foil sarking consists of a core of reinforcing material (often woven polyethylene or a polymer laminate) faced on one or both sides with aluminium foil. The foil surface is highly reflective, which is what gives it most of its thermal performance benefit. Reflective sarking works by reflecting radiant heat — both solar radiant heat trying to enter the roof space in summer, and the heat of the building trying to escape in winter.
Reflective foil sarking is effective, affordable, and widely used. It’s available in single-sided (one foil face) and double-sided (two foil faces) configurations, and in vapour-permeable and non-permeable versions. The right specification depends on the roof type, pitch, and ventilation conditions.
Breathable (Vapour-Permeable) Sarking
Breathable sarking products are designed to allow water vapour to pass through the membrane while still resisting liquid water. This is important in lower-pitch roof applications, where condensation management is more critical, and in climates where significant temperature differentials between inside and outside create conditions for moisture accumulation in roof spaces. Breathable sarking allows moisture that does get into the roof space to escape as vapour rather than accumulating and causing problems.
Non-Reflective Polymer Sarking
Non-reflective sarking products — typically heavier polymer membranes — are used in specific applications where the reflective property isn’t needed but a robust waterproof underlay is required. These are more commonly used under metal roofing than under tiles.
Thermal Performance Benefits
In the Coffs Harbour climate, the thermal benefits of sarking are very real. During summer, the region receives intense solar radiation, and an unsealed, unsarked tile roof allows significant radiant heat to enter the roof space. This radiant heat transfer heats up the roof space dramatically, which in turn increases the heat load on the ceiling below and drives up cooling energy consumption.
Reflective foil sarking can reduce radiant heat transfer through the roof by a substantial margin. The exact benefit depends on the roof type, orientation, and insulation levels, but in practical terms, homeowners with properly installed reflective sarking often report noticeably cooler ceiling areas and reduced air conditioning running time during the summer months.
In winter, the reverse effect applies — sarking reduces radiant heat loss through the roof from the warm interior, which helps maintain comfortable temperatures inside with less heating energy. The efficiency gains are particularly significant in homes with limited insulation in the ceiling space.
It’s worth noting that sarking works best in combination with adequate ceiling insulation. Sarking and insulation are complementary — sarking reduces radiant heat transfer, while batts or bulk insulation reduce conductive heat transfer. The combination is significantly more effective than either alone.
Moisture and Secondary Waterproofing Benefits
Tile roofs are designed to shed water by their overlapping profile — water runs from tile to tile and eventually off the edge into the gutters. Under normal conditions, very little water gets past the tiles. But extreme weather conditions can drive water in unexpected ways: heavy horizontal rain, storm water backing up under tiles at low points, or ice (on the rare occasions Coffs Harbour gets frosts) can all allow water to get under tiles and into the roof space.
Sarking provides a secondary waterproofing layer in these circumstances. Instead of water entering the roof space and dripping onto the ceiling, any water that gets past the tiles runs down the slope of the sarking (which follows the roof’s pitch, guided by the battens above it) and drains safely into the gutters at the eaves.
This secondary waterproofing function is particularly valuable during construction — a sarked roof frame is protected from rain damage even if the tiles haven’t been laid yet, which can be important in a climate like Coffs Harbour’s where rain events can interrupt construction schedules.
Building Code Requirements
The National Construction Code (NCC, formerly the Building Code of Australia) sets out requirements for roof sarking under various conditions. Under the NCC, sarking is required for certain roof types and configurations, including:
- Roofs in designated bushfire attack level (BAL) zones of BAL-12.5 and above, where sarking provides ember protection
- Certain roof configurations where condensation risk is elevated
- Metal-clad roofs in specific climate zones
Even where sarking isn’t strictly mandatory under the Code for a particular project, it’s often specified by engineers or building designers as a risk-mitigation measure. And for new tile roof installations in the Coffs Harbour coastal environment, the practical benefits are significant enough that Nathan installs it as a standard element of every new tile roof job regardless of regulatory requirements.
When Is Sarking Installed?
Sarking is installed as part of a new roof installation or a complete re-roof (full tile replacement). It’s installed after the rafters are in place but before the battens are fixed — the sarking drapes between the rafters, and the battens are then fixed through the sarking into the rafters, holding the sarking in position and providing the fixing surface for the tiles above.
Because sarking sits under the tiles and battens, it’s not possible to add sarking to an existing tiled roof without lifting the tiles and battens to install it. If your current roof is being fully retiled as part of a restoration or replacement project, that’s the ideal time to add sarking if it’s not already present.
During a re-roof involving full tile removal, if the existing roof has old, degraded sarking — or no sarking at all — Nathan recommends installing new sarking as part of the project. The additional cost is relatively modest when weighed against the thermal and waterproofing benefits over the life of the new roof.
Coffs Harbour Climate Context
Coffs Harbour’s climate is classified as humid subtropical — warm to hot, humid summers with significant rainfall (the region averages around 1,700mm annually, with most falling in summer), and mild winters. This climate creates specific considerations for roof design:
- High summer solar radiation makes reflective sarking particularly effective at reducing cooling loads
- High humidity and significant rainfall make secondary waterproofing and moisture management important
- Salt-laden coastal air can affect some materials, though it doesn’t directly affect sarking performance
- The combination of heat and moisture creates conditions favourable for biological growth in poorly ventilated roof spaces — sarking doesn’t prevent this but does reduce moisture ingress that contributes to it
Nathan selects sarking products that are appropriate for the Coffs Harbour coastal environment and installs them correctly to maximise the long-term performance benefit.
For more information on our full range of roofing services, visit our services page. For information specifically about new roof installations where sarking is included, see our new roof installation page.
Ask About Sarking on Your Next Roof Project
If you’re planning a new roof installation or a complete tile replacement and want to know whether sarking is right for your project — and what type of sarking is best for your specific roof — give Nathan a call. He can advise on the options and include sarking in your quote so you can make an informed decision.
Call (02) 6638 9959 to book your free on-site inspection. We service Coffs Harbour and surrounding areas including Sawtell, Toormina, Moonee Beach, Woolgoolga, and Bellingen.
Frequently Asked Questions About Roof Sarking
Is sarking required by law in Coffs Harbour?
The requirement for sarking under the National Construction Code depends on the specific circumstances of the project. For new builds in bushfire-prone land (BAL-12.5 and above), sarking is mandatory under the bushfire provisions. For other new installations, the requirement depends on the roof type, pitch, and climate zone. Even when sarking isn’t strictly required, Nathan recommends it as a matter of best practice for all new tile roof installations in the Coffs Harbour coastal environment.
Can sarking be added to an existing roof?
Sarking cannot be installed under existing tiles without removing them. However, when a full tile replacement is being carried out — whether as part of a major restoration or a complete re-roof — installing sarking at the same time adds relatively modest cost for a significant long-term benefit. If your roof is being fully retiled, Nathan will always discuss the option of adding sarking as part of that project.
Does sarking replace ceiling insulation?
No. Sarking and ceiling insulation serve different but complementary functions. Sarking primarily reduces radiant heat transfer — it reflects heat rather than absorbing and re-radiating it. Ceiling insulation (batts or blown insulation in the ceiling cavity) primarily reduces conductive heat transfer — the flow of heat through solid materials. Both are needed for comprehensive thermal performance. Sarking alone will improve comfort but won’t replace the thermal resistance that proper ceiling insulation provides.
How long does sarking last?
Quality roof sarking products typically have a service life of 50 years or more — significantly longer than the tiles above them in many cases. Foil sarking can degrade over very long periods due to UV exposure (if it’s not properly covered by tiles and battens) and in very high-humidity environments, but in a correctly installed application, sarking should outlast the first and possibly the second set of tiles installed over it.
Does sarking affect roof ventilation?
Sarking does affect roof space ventilation, and this is a consideration in product selection and installation. Non-permeable sarking effectively seals the underside of the tile surface, which means the roof space needs to be ventilated separately to prevent moisture accumulation. Vapour-permeable sarking allows moisture to pass through the membrane, which reduces (though doesn’t eliminate) the ventilation requirement. For all sarked roofs, adequate eave and ridge ventilation is important, and Nathan ensures the ventilation design is appropriate for the sarking product selected.
Sarking as Part of Your New Roof
If you’re planning a new tile roof installation or a complete tile replacement, ask Nathan about including sarking in the specification. He can explain the options, recommend the appropriate product for your specific roof and climate conditions, and include sarking in your quote so you can make an informed decision about whether to include it.
The incremental cost of sarking when it’s installed as part of a new roof is modest relative to the total project cost, and the thermal and waterproofing benefits compound over the decades of the roof’s life. It’s one of those investments that’s easy to justify when you think about the long-term outcome.
Nathan Locke is licensed, insured, and has 25 years of roofing experience in the Coffs Harbour area. Every new roof installation comes with a 10 Year Warranty. Call him on (02) 6638 9959 to discuss your project and arrange a free on-site assessment.