Roof Sarking Breathable Roofing Felt

What Is Roof Sarking?

Roof sarking is the membrane layer installed beneath roof tiles or metal sheeting. It is the roof's second line of defence: it stops wind-driven rain and dust from entering the roof cavity while letting moisture vapour escape from the structure. Australian builders call it sarking; UK fitters call it a breather membrane or roofing underlay; US crews call it a roof underlayment. Same job, same principle, different names.

Eastopo manufactures a 3-layer polyolefin (PO) breathable roofing felt - sold to Australian builders as breathable sarking - in our own factory and exported as rolls for distributors, builders and roofing contractors across Australia, New Zealand, the UK and Europe. This page focuses on the Australian market: what to specify, which grade fits which roof, and how factory-direct supply changes your landed cost.

Breathable Sarking vs Bitumen Sarking Felt

Traditional sarking felt is bitumen-impregnated. It sheds water, but it is not vapour permeable: moisture trapped under the felt condenses on its cold underside every night. That is why most roof builds in Australia today specify a vapour permeable sarking instead.

For a distributor, the difference is simple: a vapour permeable sarking roll can be stocked for both tiled and metal roofs, while bitumen felt limits you to ventilated builds and carries a condensation risk the specifier has to design around.

Why Australian Roof Builds Specify Sarking

Australian building regulations require tiled roofs below an 18 degree pitch to be sarked, and metal roof construction is sarked as standard in most climate zones. Two jobs drive the requirement:

• Condensation control. A vapour permeable sarking keeps the insulation dry, which protects both the R-value and the timber frame. Roofs without sarking develop black spot mould on rafters within 18 to 24 months in high humidity zones.
• Wind-driven rain and dust. A sarked roof cavity stays dry and clean, which matters for metal roof purlins and for the underside of tiles in bushfire-prone areas.

Specifiers and builders also order sarking with an eye on summer heat. A reflective foil sarking adds radiant heat rejection, while a vapour permeable sarking trades that for breathability. The two are different products for different roof builds - one factory supplying both means your distributor can hold both lines on one invoice.

Sarking Specifications for Trade Buyers

Wholesale buyers compare sarking on five numbers. Here is the full matrix for our breathable sarking felt:

Send your target gsm and wind zone and we match the grade. Most Australian distributors start with 120 to 150 gsm stock rolls and add a heavier grade for metal roof projects.

Roof Sarking Installation Essentials

Installation details decide whether the sarking performs. These are the points your customers will ask about:

• Lap width. Lap 150 mm minimum, and 200 mm on pitches below 15 degrees. A 50 mm lap saves two minutes per run and leaks for the life of the roof.
• Fixing. Use compatible tape at every nail penetration and seal all laps. Sarking is a secondary layer - the tiles or metal sheet still carry the primary waterproofing job.
• Slope direction. Lay the sarking so the top sheet laps over the lower sheet, following the water flow. On sarked roofs below 18 degrees, keep the laps sealed and run the sheet parallel to the eaves.
• Ventilation. Vapour permeable sarking removes the need for a vented void above the insulation in most builds, but keep ridge and eaves ventilation per the roof design.

The Real Cost of Skipping Sarking

Sarking failures rarely show up at handover. They show up at year two or three, when the snagging period is over and the roofer is long gone.

Condensation on a non-breathable layer. Lay bitumen felt over a warm roof without a vented void and condensation forms on its cold underside every night. The insulation wets out, the R-value drops, and rafters develop black spot mould within 18 to 24 months. Contractors end up stripping and replacing whole roof decks - the cheapest felt in the catalogue becomes the most expensive roof in the street.

Sarking left exposed too long. UV turns a standard sarking brittle. On the next windy day it splits along the lap line and wind-driven rain enters above the insulation. Our 3 to 4 month UV rating covers a normal build programme when site slips; beyond that, protect the roll or order the UV-stable grade.

Wrong layer for the job. Put a high-resistance vapour barrier where a vapour permeable sarking belongs and you seal moisture inside the structure. The dew point moves into the insulation and condensation collects where nobody can see it until the ceiling stains.

OEM Sarking Supply from a Chinese Factory

Eastopo is a factory-direct manufacturer, not a trading house. The sarking line runs in our own plant with the same quality control as our EN-certified breathable membrane: every production batch is checked for Sd value, water tightness and tensile strength before it leaves the line, and roll weights are verified against the declared gsm.

For Australian distributors, factory-direct means three things:

• Private label. Print your brand on the selvedge and on the packaging. Your customers see your name on the roll, not ours.
• Custom rolls. gsm from 60 to 220, roll width and length to order, so your stock range matches your market instead of the other way around.
• One supplier, both lines. Order vapour permeable sarking, foil vapour barrier sarking and building wrap for wall cavities from the same factory, on one invoice, with one freight consolidation.

Certification is verified and current: verified to EN 13859-1 by ICR, water tightness Class W1, and a TUV-audited quality system at the Haining plant. Local compliance for the Australian market - including any state-level sarking requirements - is confirmed at specification time with your importer or distributor.

Sarking Roll Formats and Customisation

Standard stock format is 1.5 m x 50 m at 75 m² per roll. Customisation covers the range Australian distributors actually order:

Incoterms are EXW, FOB, CFR and CIF - our standard four, nothing hidden. Send your target gsm, roll size and quantity; we quote price, MOQ and lead time within one working day.

Frequently Asked Questions

Q1: What is the difference between sarking and a breathable membrane?

In Australia, sarking is the general name for the membrane layer under roof tiles or metal sheeting. A vapour permeable sarking - the type most modern roofs specify - is a breathable membrane: it blocks wind-driven rain and dust while letting water vapour escape. The terms describe the same product in different markets.

Q2: Is sarking required on tiled roofs in Australia?

Australian building regulations require sarking on tiled roofs below an 18 degree pitch, and metal roof construction is sarked as standard in most climate zones. Always confirm the current requirement for your state and roof design with your certifier or building surveyor before ordering.

Q3: Can breathable sarking replace traditional bitumen felt?

Yes, on most tiled and metal roofs. Vapour permeable sarking meets EN 13859-1 with water tightness Class W1, is lighter to carry and cut than bitumen felt, and removes the condensation risk that bitumen felt creates in unventilated builds. Match the gsm to the wind zone and batten spacing, and never treat sarking as primary waterproofing.

Q4: What Sd value should a vapour permeable sarking have?

Sd is the equivalent air layer thickness for water vapour diffusion, in metres. Low Sd - around 0.02 to 0.035 m - means the layer breathes, which is what an outer sarking needs. High Sd, above 100 m, means the layer is a near-total vapour barrier, which is a different product for the warm side of the insulation.

Q5: Do you supply OEM sarking rolls for Australian distributors?

Yes. We customise gsm from 60 to 220, roll width and length, and print your branding on the selvedge with private-label packaging. Standard stock format is 1.5 m x 50 m at 75 m² per roll. Send your target spec and we confirm feasibility and lead time within one working day.

Q6: What is the minimum order and lead time for wholesale sarking?

MOQ and lead time depend on the product line and whether rolls are stock or customised. Stock 120 to 150 gsm rolls ship faster than bespoke gsm or printed rolls. Ask for a quote with your target gsm, roll size and quantity; we reply within one working day with pricing, MOQ and schedule.

About the Author

Written by J. Mao - Eastopo New Materials. J. Mao works directly with Australian, UK and European distributors on breathable membrane and sarking specifications, EN 13859-1 compliance and OEM supply. Questions on grades, samples or project specs: mj@eastopo.com or +86 193 5725 8106.

Get a Quote for Your Sarking Order

Send us your roof spec - target gsm, wind zone, roll size and quantity - and we will match it to the right sarking grade within one working day. Email mj@eastopo.com, WhatsApp +86 193 5725 8106, or use the inquiry form and ask for the sarking price list.