What Self-Drilling Screw Should I Use for Metal Roofing?

The roofing standard: hex washer head with an EPDM sealing washer

Every screw hole in a metal roof is a potential leak and a potential corrosion start, so roofing screws are specified as a system: a self-drilling screw to DIN 7504 with a hex washer head, assembled with a bonded EPDM sealing washer. The hex head drives with a standard nut-setter, the wide washer spreads clamping load so the sheet does not dimple, and the EPDM rubber compresses under the washer to seal the hole against rain. This is the configuration that WTFasteners (Hebei W.T Fasteners Co., Ltd.), a source factory in Yongnian, Handan, China, catalogs for roofing and cladding work as part of its DIN 7504 self-drilling screw range.

What makes the screw "self-drilling" is the fluted drill point at its tip: it cuts its own hole through steel purlins, girts and light structural sections, so crews fix sheet to frame in a single pass with no pilot drilling. A plain self-tapping screw only forms a thread and cannot cut steel on its own — that single-step installation is why roofing contractors buy self-drilling screws by the carton and by the container, because a roof has thousands of fixing points.

Match the size and length to your build-up

Catalog sizes run #6 through #14, and for roofing the common workhorses are #12 and #14: the larger shanks hold pull-out values in thin sheet, and their drill points handle the purlin beneath. Length is chosen from the total clamped thickness — sheet, insulation or air gap, washer stack — plus enough extra for the drill point to break fully through the far side of the supporting steel. Catalog washer-head screws run from 19 mm up to 300 mm to cover everything from single-skin cladding to deep sandwich-panel build-ups, so measure the build-up first and match the length from the catalog rather than guessing on site.

Drill points are graded by the steel thickness they can cut, and the rule is simple: the point must be rated for the thickest steel in the stack. Send the sheet gauge and the purlin thickness with the inquiry and the screw can be matched from the catalog to the actual job.

Choose a finish for the exposure, not just the price

The finish decides how long the roof stays a roof. Bright zinc plating suits sheltered, indoor-adjacent use; for a roof open to weather, galvanized (G.I.), Dacromet or Ruspert coatings are the catalog options with real outdoor credentials. Coastal sites, agricultural buildings and humid export markets are exactly where the upgraded coating pays for itself — the screw costs a little more, but it is the cheapest line on the order and the most expensive thing to replace on a finished roof.

The EPDM washer is part of the corrosion strategy too: by sealing the hole it keeps water off the cut edge of the sheet, which is where red rust usually starts. A correctly sealed fixing point protects both the screw and the sheet around it.

Installation details that decide service life

Two details on the gun decide whether the seal lasts. Drive the screw perpendicular to the sheet so the washer seats evenly, and stop when the EPDM is compressed to a slight, visible bulge — over-driving crushes the washer and dimples the sheet, while under-driving leaves a gap for capillary water. On long runs, use a depth-sensitive screw gun so every one of the thousand fixings gets the same setting.

Requesting roofing screws factory-direct

A quotation needs the head style, size, length, finish, quantity and destination. Because the screws, washers and coatings come from one factory program in Handan, lots stay consistent and export packing is aligned before shipment. Send the specification to WTFasteners at WhatsApp +86 138 0310 6448 or postmaster@wtfastener.com for a factory-direct quotation.