In high winds, metal roofs rarely fail because the panels are weak. They fail because the connection between the panel and the structure fails, usually at a corner. When ordering roofing for projects in high-wind areas, it’s important to understand the main risks, the principles of wind lift, and how screw choice and installation contribute to wind-resistant roofs.
This guide is not a substitute for a thorough understanding of building regulations and manufacturer guidelines. Wind loads are calculated under ASCE 7 and enforced through the International Building Code and local building regulations.
Why Wind Uplift Is a Fastener Issue
It is tempting to picture wind damage as being caused by wind pushing a roof down or across. Although wind does cause lateral loading, the main problem is uplift. When fast-flowing air passes over a roof, it speeds up. The faster the air moves, the less pressure it exerts on the surface beneath it.
The result is suction. Instead of being pressed down, the roof is pulled up. It’s the same principle that generates lift in airplane wings.
On a through-fastened metal roof, that upward force is transferred into the roofing fasteners. If they hold, the roof stays on. If they don’t, the panel goes. Wind is also gusty rather than steady, so the load is not applied once and released. It cycles up and down thousands of times during a storm. Repeated uplift can fatigue the connection around the screw and slowly work it loose.
What Determines a Roofing Fastener’s Holding Power
Pull-out resistance is the force required to withdraw a fastener from the substrate. Several factors influence a screw’s ability to resist withdrawal.
- Screw diameter. Larger diameters increase thread bearing area, requiring more substrate material to shear or displace before failure.
- Thread design. Thread pitch and depth need to match the substrate. Coarse, deep threads grip wood well. Finer pitches engage more threads per inch in thin steel.
- Embedment depth. Pull-out resistance increases with engaged thread length. Too little engagement leaves the screw vulnerable to wind loosening.
- Substrate type and thickness. A screw can only be as strong as the material it is anchored into. In wood, species and density affect withdrawal capacity. In steel, plate thickness and tensile strength matter most, and the ratio of steel thickness to thread pitch determines whether the screw holds or strips.
In practice, roll formers and panel manufacturers should work back from the expected uplift load and intended substrate to find a screw with the diameter, thread, and length to deliver the required pull-out value.
Metal Roof Screw Patterns by Wind Zone
Wind pressure is not distributed evenly across a roof. When wind hits a building and rolls up over the walls, it separates at the edges and accelerates around the corners, generating localized suction that is higher than in the middle of the roof. To account for that, the roof area is divided into three zones.
- Zone 1, the field of the roof, is the large interior area where airflow has settled, and uplift pressures are at their lowest.
- Zone 2, the perimeter strip, runs along the edges where wind separating from the walls creates higher suction.
- Zone 3, the corners, is where wind curling over two edges at once forms conical vortices that produce the most intense wind uplift on the roof.
A common starting point for a through-fastened panel is a screw in every other major rib in Zone 1, every rib in Zone 2, and every rib plus intermediates in Zone 3. Other schedules express the same pattern in inches between fasteners along the purlin: roughly twelve inches apart in the field, six at the perimeter, and four at the corners.
Choosing the Right Roofing Fasteners for Wind Resistance
A roof designed to last forty years needs fasteners engineered to match. Atlas’s metal-to-metal and metal-to-wood lines cover the full range of roofing fasteners that a high-wind roof construction project is likely to call for.
