The screw is the smallest, cheapest part of a metal roof — and the one that fails first on the coast. Here's what the corrosion classes actually mean, and why insisting on Class 4 fixings is the single most important spec on a Northern Rivers roof.
The AS 3566 classes, explained
Roofing screws are rated to AS 3566 by corrosion resistance: Class 1 (mild), Class 2 (moderate), Class 3 (severe) and Class 4 (very severe / coastal). The class reflects the coating on the screw and its expected life in different environments. Class 4 is the highest, designed for coastal and other aggressive environments.
Why Class 4 matters on the Northern Rivers
Within kilometres of the surf, salt spray is constant. A Class 2 or Class 3 screw will rust years before a Class 4 one — and once the screw rusts, the washer perishes, water gets in, and the roof leaks. The difference in cost between classes is tiny; the difference in lifespan is years.
The washer matters as much as the screw
The rubber washer under the screw head is what actually seals the hole. Even a Class 4 screw with a cheap washer will leak once the washer perishes. We use screws with quality EPDM washers rated for UV and salt — the washer and the screw need to last together.
Oversized screws for stripped holes
When an old screw is removed, the hole can be stripped or enlarged. A same-size screw won't grip. We step up to an oversized screw for a solid bite, so the new fixing actually holds — re-screwing into a loose hole is a waste of a new screw.
Profile matters
Corrugated, trimdek and klip-lok profiles need different screw types and washers. Using the wrong profile screw can damage the sheet or fail to seal. We match the screw to the sheet profile, every time.
What to ask your roofer
If you're getting a metal roof repaired or re-screwed on the Northern Rivers, ask one question: 'Are you using Class 4 screws?' If the answer is anything other than a clear yes, find a different roofer. It's the cheapest spec that matters most on the coast.
Questions
Common questions
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We're local to Lennox Head and cover the whole Northern Rivers. Every job is photo-documented and warranted.
Coastal Roofing Repairs
Local Northern Rivers roofers · 28 years on the tools · insured
Written by the Coastal Roofing Repairs team, 28 years roofing on the NSW North Coast. We work on coastal metal and tile roofs every day — these guides come straight from what we see on the tools, not a marketing desk.
