Views: 100 Author: Liu Yanhui Publish Time: 2026-04-14 Origin: Tsingri Screw
Choosing the wrong metal roofing screw is one of the most expensive mistakes a contractor or specifier can make — not because the screws themselves cost a fortune, but because failures are discovered after installation, when remediation costs multiply fast.
A leaking roof. A detached cladding panel. A warranty dispute. All of it traces back to a fastener that was wrong for the application, the substrate, or the environment.
This guide covers everything you need to know to specify metal roofing screws correctly: types, materials, surface treatments, washer options, and how to read a screw specification so you never get caught out by a mismatched fastener again.
Metal roofing screws are self-drilling, self-tapping fasteners designed to penetrate metal substrates without pre-drilling. The drill point at the tip cuts through the material, while the threaded shank pulls the sheet tight and creates its own thread in the base metal.
This single-step installation — no pilot hole, no separate drill bit — is what makes them the fastener of choice across steel roofing and cladding systems worldwide.
Two terms are often used interchangeably but describe subtly different tools:
Self-tapping screws: tap their own thread into a pre-drilled hole
Self-drilling screws: drill the hole and tap the thread in one operation
For metal roofing and cladding, self-drilling screws are the standard. The drill point geometry determines how thick a steel substrate the screw can penetrate, which is why selecting the right point is non-negotiable
Not all roofing screws are designed for the same job. Broadly, metal construction screws fall into three application categories:
1. Valley Fixing Fasteners (Sheet-to-Steel)
Valley fixing fasteners are used to secure profiled steel sheeting directly onto a steel substrate — think roofing sheets fixed to purlins, or wall cladding panels fixed to steel framing. They are installed through the valley (low point) of the profile, which is why the term “valley fixing” is used.
Key features:
Hex washer head or hex indented washer head
EPDM rubber washer or SS304+EPDM bonded washer for weatherproofing
Available in #12 (5.5mm) and #14 (6.3mm) gauge
Drilling capacity: #12 up to 6.0mm steel, #14 up to 7.0mm steel
Sizes from 12-14×25mm through 14-14×95mm
The washer is critical. It creates the weather seal at the fastener point. A failed or degraded washer is one of the most common causes of roof leaks — which is why specifying a bonded SS304+EPDM washer (rather than a loose rubber washer) is recommended for long-term performance.
2. Structure Fixing Fasteners (Heavy Duty)
Structure fixing screws are designed for fastening steel plate to thick steel structures — purlin-to-rafter connections, column cladding, and heavy steel framing assemblies. They use a #5 drill point, which is significantly more aggressive than the standard #3 point and can penetrate steel plate up to 12.5mm thick.
Key features:
Phillips pan head or hex washer head
Fine thread (#24) for faster drilling speed and stronger fastening in steel
#5 point eliminates the need for pre-drilling even in thick steel
Available in #12 (5.5mm) and #14 (6.3mm) gauge
Sizes from 12-24×32mm through 14-24×95mm
The fine thread design (#24 threads per inch) provides two advantages: faster installation speed and a stronger grip in high-tensile steel, compared to coarse thread designs. An additional engineering detail worth noting — the thread geometry on structure fixing screws is designed to prevent iron filings from accumulating in the thread, which reduces the risk of corrosion initiating at the fastener point.
3. Light Steel Keel Screws (Thin Sheet & Wall Fixing)
This category covers fasteners for lighter applications: fixing thin metal sheet to light steel framing, fixing wall panels to structures, and fixing fibreboard or OSB to steel.
Products in this category include:
Hex intended washer head (wall/structure): #10 gauge, 4.8mm diameter, for fixing wall panels to structure or pull-out components. Max steel thickness 4.0mm.
Single thread thin sheet screws: Designed for 1×1.0mm or 2×0.75mm thin sheet metal. Sharp point delivers fast drill speed with minimal material distortion.
Double thread thin sheet screws (bi-metal): For fixing aluminium and steel profile sheets together. Double thread allows drilling through up to 2mm steel plate; bi-metal construction provides stainless corrosion resistance.
Expansion wings self-drilling screws: For fixing cement fireboard, wood, or OSB to steel. The expansion wings drill through the board, then break off upon contact with the steel substrate, allowing the thread to engage the steel cleanly. Embossed head prevents over-driving.
Material selection is where most specification errors occur. The choice depends on three factors: corrosion environment, substrate materials, and project lifespan requirements.
Carbon Steel 1022A / 10B21
Carbon steel is the most commonly used material for roofing screws. It offers excellent mechanical properties after heat treatment — high tensile strength, good hardness, and reliable drill performance.
Surface treatment is essential. Bare carbon steel will rust rapidly in outdoor environments, so all carbon steel roofing screws must carry a corrosion-resistant coating:
Ruspert coating (AS3566 Class 3 or Class 4): A multi-layer proprietary coating that provides 480–1000+ hours of salt spray resistance. Class 3 is suitable for standard inland environments; Class 4 for coastal or industrial zones.
Zinc plated: Basic protection, suitable for dry or sheltered applications.
REXIUBAO coating: A Chinese market-standard equivalent offering comparable performance to Ruspert.
Best for: Standard commercial and industrial roofing, cost-sensitive projects where the environment is not classified as corrosive.
Stainless Steel 410
SS410 is a martensitic stainless steel that can be heat-treated to achieve the hardness required for self-drilling applications. It provides significantly better corrosion resistance than coated carbon steel without the cost of austenitic stainless grades.
Note that SS410 is magnetic and has moderate corrosion resistance — it is not suitable for marine environments or continuous moisture exposure.
Best for: Projects requiring improved corrosion resistance over carbon steel, moderate coastal exposure, or where visible fasteners demand a cleaner aesthetic.
Bi-metal: SS304/316 Body + SCM435 Drill Point
Bi-metal construction is the engineering solution to a specific problem: you need the corrosion resistance of stainless steel, but stainless steel alone is too soft to drill through thick steel plate reliably.
The solution is to weld or join two materials:
SCM435 drill point: A chromium-molybdenum alloy steel with high hardness after heat treatment. It drills efficiently through steel substrates.
SS304 or SS316 body, shank, and thread: Full austenitic stainless steel provides exceptional corrosion resistance for the fastener’s service life.
This combination is essential when fastening aluminium sheeting to steel substructures, where using a carbon steel fastener would create a galvanic corrosion cell at the contact point, leading to accelerated corrosion of both materials.
Best for: Coastal environments, marine zones, solar panel installations, aluminium-to-steel connections, and any application where fastener longevity must match a 20–30 year system lifespan.
For contractors working across different project environments, understanding the Ruspert / AS3566 classification is important for correct specification.
Most commercial roofing projects specify Class 3 as the minimum. Projects within 1km of a coastline, in industrial zones with chemical exposure, or in tropical climates should specify Class 4 or upgrade to stainless steel fasteners.
Custom coatings are available for specific project requirements — NSS (neutral salt spray) testing from 500 to 2000 hours, and Kesternich (SO₂ corrosion) testing from 5 to 30 cycles.
How to Read a Roofing Screw Specification
A roofing screw specification string like 12-14×45mm carries the following information:
12 = Thread diameter in gauge (#12 = 5.5mm / #14 = 6.3mm / #15 = 6.99mm)
14 = Threads per inch (TPI) — thread pitch
×45mm = Total length of the screw
For insulation roofing fasteners, you will encounter specifications like #14 Heavy Duty, 4" length — this follows the imperial format common in North American roofing applications.
Effective fixing thickness refers to the clamping range — the total thickness of material that can be clamped between the head and the substrate. This is distinct from the total screw length, and it is what you use when matching screw length to insulation board thickness.
EPDM Washer vs. SS304+EPDM Bonded Washer
The washer is the weather seal. Its failure is what turns a screw hole into a leak point.
Standard EPDM washer:
Rubber washer bonded to a steel backing plate
Compresses under the screw head to form a seal
Suitable for most standard applications
Can degrade over time with UV exposure if not fully compressed
SS304+EPDM bonded washer:
Stainless steel backing plate with EPDM layer chemically bonded to it
No risk of the washer separating from the metal backing
Stainless backing resists corrosion at the fastener head
Preferred for Class 3/Class 4 environments and long-service installations
For roofing applications with a design life of 20+ years, SS304+EPDM bonded washers are the correct specification. The marginal additional cost is insignificant against the cost of a leaking roof.
Drill Point Sizes: #3 vs. #5
The drill point is the business end of a self-drilling screw. Its size determines the maximum steel thickness it can penetrate in a single operation.
Using a #3 point on steel thicker than its rated capacity will result in the screw stalling, a stripped drill point, or a fastener that has not fully engaged the substrate. A #5 point on thin sheet will over-drill, removing material and weakening the connection.
Before finalising your fastener specification, confirm the following:
Substrate thickness — what is the steel gauge of the purlin, frame, or structure?
Sheet/panel material — steel, aluminium, or composite?
Total clamping thickness — sheet + any foam backing or thermal break?
Environment classification — inland, coastal, industrial, marine?
Required surface treatment — Class 3, Class 4, or custom NSS/Kesternich?
Washer type — EPDM or SS304+EPDM bonded?
Head type — hex for power tool installation, or countersunk for flush finish?
Drive type — Phillips, Torx, or hex?
Project lifespan — standard warranty or 25–30 year design life?
Running through this checklist before procurement takes five minutes. Getting it wrong takes considerably longer to fix.
Metal roofing screws are a small line item on any project budget, but they carry an outsized responsibility. The right fastener — correctly matched to the substrate, environment, and application — will perform for the life of the building. The wrong one becomes a liability.
The key variables are material (carbon steel, SS410, or bi-metal), surface treatment (Class 3/4 or stainless), drill point (#3 or #5), washer specification (EPDM or bonded SS304+EPDM), and thread design (coarse for sheet, fine for structure).
If your project has requirements that fall outside standard specifications, contact our technical team at info@tsingri.com or visit www.tsingri.com to request a custom quotation or specification review.
