Repair Systems — 04 — Roofing Defects
Roofing screws and sealing washers — metal sheet roof
Class 3 or Class 4 hex-head self-drilling roofing screws with EPDM sealing washers are the primary fixing for metal sheet roofing into steel purlins. The corrosion class must be selected to suit the environment under AS 3566.2. Screw length, washer compression and correct engagement depth in the purlin are critical for both weathertightness and structural performance.
Roofing screws and sealing washers — what they are
Roofing screws are self-drilling hex-head fasteners with an integrated EPDM-backed sealing washer, used to fix metal roofing sheets (corrugated, Trimdek, cappings) to steel purlins. The EPDM washer compresses against the face of the sheet to seal the screw penetration against water entry. Corrosion class (AS 3566.2 Class 3 or Class 4) must be selected to suit the environment — coastal buildings require Class 4.
Technical Reference
Class 3 vs Class 4 corrosion selection, screw length, EPDM washer compression and replacement of corroded fixings
Product Reference
3 products — Buildex Class 3, Buildex Class 4 and other AS 3566.2-compliant roofing screws
Buildex Climaseal — Class 3
Class 3 corrosion-rated hex-head self-drilling roofing screw; 14g standard; Type 17 or Type 16 point; EPDM sealing washer; AS 3566.2 compliant
Product type
Class 3 roofing screw — hex head — EPDM washer — AS 3566.2
System description
Buildex Climaseal is the most widely used Class 3 roofing screw in Australia, specified for metal sheet roofing in non-coastal, non-industrial environments. The screw is a self-drilling hex-head fastener with an EPDM-backed sealing washer that compresses against the face of the sheet to create a watertight seal around the penetration. Class 3 corrosion rating under AS 3566.2 is appropriate for most inland and suburban environments, including Class 2 strata buildings located more than 500m from coastal influence. Available in multiple lengths to suit sheet BMT and purlin depth — confirm screw length against the purlin wall thickness.
Technical properties
- Corrosion class: AS 3566.2 Class 3 — suitable for inland and suburban environments
- Head type: hex head (hexagonal drive) with integrated EPDM sealing washer
- Gauge: 14g (5.5mm shank) — standard for metal sheet roofing into steel purlins
- Point type: Type 17 (self-drilling with auger tip) for steel-to-steel; Type 16 also available
- Lengths: 25mm, 35mm, 50mm, 65mm — select to suit sheet + purlin thickness; confirm minimum 3 full thread turns in purlin
- Wafer/dome head option for specific applications — confirm with Buildex
- AS 3566.2 Class 3 compliant
Limitations
- Class 3 is NOT suitable within 500m of a surf coast or in industrial/atmospheric pollution environments — use Class 4 instead
- EPDM washer must compress evenly against the sheet — over-driving collapses the washer and reduces the seal; under-driving leaves a gap
- Screw must penetrate the purlin by a minimum of 3 full thread turns — confirm screw length against purlin flange thickness
- Do not reuse screws where removed — EPDM washer compression memory is not recoverable
- Class 3 screws must not be used with natural zinc sheet — use manufacturer-approved zinc screws
Procurement
Buildex distributors and roofing merchants nationally. Available through major trade merchants, hardware chains and specialist roofing fastener suppliers.
Confirm suitability with the current manufacturer TDS before specifying or applying.
Buildex Galvadrive — Class 4
Class 4 corrosion-rated hex-head self-drilling roofing screw; 14g; EPDM sealing washer; AS 3566.2 compliant; for coastal and corrosive environments
Product type
Class 4 roofing screw — hex head — EPDM washer — AS 3566.2
System description
Buildex Galvadrive and equivalent Class 4 roofing screws are specified where the corrosive environment demands greater corrosion protection than Class 3. Class 4 screws have a heavier corrosion-resistant coating (typically a mechanically applied zinc plus additional coating) and are required for buildings within 500m of a surf coast, within 1km of breaking surf under AS 4055 conditions, or in industrial environments with airborne corrosives. On Class 2 strata buildings in coastal areas, structural engineers and roofing consultants typically specify Class 4 fasteners as standard. Using Class 3 screws in coastal or industrial environments results in premature corrosion and eventual structural failure of the fixing.
Technical properties
- Corrosion class: AS 3566.2 Class 4 — coastal, marine and industrial environments
- Head type: hex head with EPDM sealing washer
- Gauge: 14g (5.5mm shank)
- Point type: Type 17 self-drilling for steel-to-steel
- Same length range as Class 3 — confirm minimum 3 full thread turns in purlin
- AS 3566.2 Class 4 compliant
Limitations
- Heavier coating on Class 4 screws can slightly reduce self-drilling performance — use appropriate drill speed and pressure
- Class 4 does not mean corrosion-proof — in the most severe marine environments (continuous salt spray), stainless steel fasteners may be required — engineer review
- Same EPDM washer compression requirements as Class 3 — do not over-drive or under-drive
- Do not mix Class 3 and Class 4 screws in the same roof — specify one class throughout for consistency
Procurement
Buildex distributors and roofing merchants nationally. Confirm availability of Class 4 product at local merchant before specifying.
Confirm suitability with the current manufacturer TDS before specifying or applying.
Other Class 3/4 roofing screws
Elco, Simpson Strong-Tie and other AS 3566.2-compliant Class 3 and Class 4 hex-head roofing screws with EPDM sealing washers
Product type
Class 3 or 4 roofing screw — AS 3566.2 — confirm from TDS
System description
Elco Industries, Simpson Strong-Tie and other fastener manufacturers supply AS 3566.2 Class 3 and Class 4 hex-head self-drilling roofing screws with EPDM sealing washers as alternatives to Buildex products. The key selection criteria are AS 3566.2 corrosion class compliance, gauge (14g standard), point type (Type 17 for steel-to-steel), head type (hex head with integrated EPDM washer), and screw length. Confirm that any proposed alternative fastener carries an AS 3566.2 compliance certificate and is covered by the sheet manufacturer warranty conditions.
Technical properties
- AS 3566.2 Class 3 or 4 compliant — confirm corrosion class from product TDS
- Gauge: 14g — confirm from TDS
- Head: hex head with EPDM sealing washer
- Point: Type 17 self-drilling for steel purlin applications
- Lengths: 25–65mm range — confirm against purlin thickness
Limitations
- Must carry a verifiable AS 3566.2 compliance certificate — do not specify uncertified fasteners
- Check compatibility with sheet manufacturer warranty — some manufacturers specify Buildex or named equivalent
- Confirm product availability at local trade merchant before specifying
Procurement
Specialist fastener suppliers, roofing merchants and trade hardware nationally. Elco available through electrical and roofing trade distributors.
Confirm suitability with the current manufacturer TDS before specifying or applying.
Class & Brand Equivalence
Class 3 and Class 4 are NOT interchangeable — the environment determines the class. Within each class, compliant products from different brands are equivalent.
| Product A | Product B | Equivalence note |
|---|---|---|
| Buildex Climaseal Class 3 | Other Class 3 roofing screws (AS 3566.2) | Any AS 3566.2 Class 3 hex-head self-drilling 14g roofing screw with EPDM washer is technically equivalent. Confirm sheet manufacturer warranty acceptability before substituting Buildex with another brand. |
| Buildex Galvadrive Class 4 | Other Class 4 roofing screws (AS 3566.2) | Any AS 3566.2 Class 4 hex-head self-drilling 14g roofing screw with EPDM washer is technically equivalent. Confirm warranty acceptability and local availability before substituting. |
| Class 3 screws | Class 4 screws | NOT equivalent — Class 4 has a heavier corrosion-resistant coating than Class 3. Class 4 is mandatory in coastal, marine and industrial environments. Do not substitute Class 3 for Class 4 in these environments. |
System Comparison
Class 3 vs Class 4 vs other AS 3566.2-compliant screws. Confirm class selection against the corrosion environment classification.
| Attribute | Class 3 (Climaseal) | Class 4 (Galvadrive) | Other compliant |
|---|---|---|---|
| AS 3566.2 class | Class 3 | Class 4 | Class 3 or 4 (confirm) |
| Typical environment | Inland / suburban | Coastal / industrial | Confirm from TDS |
| Gauge | 14g (5.5mm) | 14g (5.5mm) | 14g (confirm) |
| Head type | Hex head | Hex head | Hex head (confirm) |
| Point type | Type 17 self-drilling | Type 17 self-drilling | Type 17 (confirm) |
| Washer | EPDM sealing washer | EPDM sealing washer | EPDM (confirm) |
| Lengths available | 25 / 35 / 50 / 65mm | 25 / 35 / 50 / 65mm | Confirm TDS |
| Min purlin thread engagement | 3 full turns | 3 full turns | 3 full turns |
Common roofing screw defects and failures:
- Corroded screws with failed EPDM washers — rust tracks down from the screw head across the sheet surface and water enters through the corroded penetration. Replace with same gauge Class 3 or 4 screws as appropriate for the environment.
- Over-driven screws — EPDM washer collapsed and torn, sealing capacity lost. Not reusable — remove and replace; use fresh screw position if thread hole is damaged.
- Under-driven screws — EPDM washer not fully compressed, gap between washer and sheet face. Water tracks under the washer into the hole. Tighten or replace.
- Wrong corrosion class — Class 3 screws in coastal environments will rust within 3–5 years. Inspect and replace all screws with appropriate Class 4 product if corrosion class mismatch is identified.
- Insufficient thread engagement in purlin — screw too short; pulls out under wind uplift. Replace with longer screw achieving 3+ full thread turns in purlin.
Disclaimer
This page provides general technical information only. Final screw class, length, quantity and spacing must be confirmed against the current manufacturer TDS, AS 3566.2, the structural engineer specification and the sheet manufacturer warranty conditions. Do not rely on this reference as a substitute for professional engineering advice.