Screw Pattern

The screw pattern on a metal roof is not arbitrary — it is engineered to resist the specific wind loads expected at each zone of the roof. Australian Standard AS 1562.1 defines four wind-load zones on a typical roof: general area, edge zone, corner zone, and ridge zone. The corner and edge zones experience significantly higher wind uplift forces than the general area, so they require a denser screw pattern — often double the fastener density of the general field. Metal roof screws are self-drilling, hex-head fasteners with a bonded neoprene washer that compresses to form a watertight seal at each penetration point. The screws are driven through the crest (top) of the corrugation on corrugated profiles and through the pan (valley) on some trapezoidal profiles. It is critical that screws are driven to the correct tension — overtightening compresses the neoprene washer beyond its elastic limit, causing it to fail prematurely, while undertightening leaves the seal incomplete. In Gippsland, wind loads vary significantly depending on location, terrain category, and the height and shape of the building. Properties in elevated or exposed positions — such as ridgeline sites in the Strzelecki Ranges or open farmland — may require higher wind-speed design ratings and correspondingly denser screw patterns. Town & Country Roofing calculates the correct screw pattern for every metal roofing installation based on the site-specific wind loading requirements.