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Self-drilling screws feature a drill-shaped point that drills its own hole and threads in one operation. Self-tapping screws require a pre-drilled pilot hole before they can tap threads into the material.
Polycarbonate roofing screws are specifically designed with larger washers or expanding features to accommodate the thermal expansion and contraction of plastic sheets, preventing cracks and leaks.
Stainless steel screws offer superior corrosion resistance and are highly recommended for coastal areas, chemical plants, or environments exposed to severe weather, whereas galvanized screws are ideal for standard outdoor applications.
The EPDM rubber washer creates a tight, waterproof seal when compressed, preventing rainwater or moisture from seeping through the drilled fastening point into the roof structure.
The screw length should be long enough to penetrate through the roofing sheet and completely engage into the underlying wood or steel purlins, typically requiring at least 15-20mm of penetration depth.
