Metal Roof Fasteners

Fasteners are the anchor points of a metal roof. In standing seam roofs they are hidden, holding clips to the deck; in exposed-fastener roofs they pass through the panel face and must also keep water out. The right fastener depends on the panel system, the metal, the substrate and the environment.

Main types

Roofing fasteners include screws, nails, staples, bolts, clips and specialised anchors. On metal roofs they fall into two groups:

• Concealed fastening: screws hold clips, or a fastening flange along the panel edge, to the deck; the next panel's seam or locking joint covers them, so nothing pierces the weather surface. Clips also let the metal expand and contract.
• Exposed (washer-head) screws: driven through the panel face, with a rubber washer, typically EPDM, under the head to seal the hole. They are used on corrugated and ribbed through-fastened sheets.
• Nails and cleats: in traditional copper roofing, copper or hardware bronze nails secure concealed copper cleats to wood decks; screws and bolts are copper, bronze, brass or 300-series stainless steel.

Materials and corrosion

Fastener metal must be compatible with the roofing metal, or moisture can drive galvanic corrosion at the connection, staining the panel and weakening the fixing:

• Copper, bronze, brass or 300-series stainless with copper roofs.
• Aluminium or stainless steel with aluminium roofs, never bare or ordinary steel.

Fastener type, number and spacing are set by the manufacturer's specifications, local building codes, roof type and wind zone. Inferior or incompatible substitutes can void manufacturer warranties.

Ageing and maintenance

Washers are usually the shortest-lived part of an exposed-fastener roof. Sunlight hardens them and daily thermal movement can loosen screws, so washers may begin to crack and screws back out after roughly 10 to 15 years, and periodic checking and re-screwing is part of maintenance. Concealed systems avoid these penetrations.

Installation

Screws should be driven square and not overtightened. Over-driven or angled fasteners distort the panel, can damage washers and contribute to visible waviness (oil canning).