Through-Fastened (Exposed-Fastener) Metal Panels

Through-fastened, or exposed-fastener, metal roofing is the most widespread and least expensive form of metal roof. Profiled sheets, either corrugated or trapezoidal (box-ribbed), are laid with side laps over a rib and screwed directly through the sheet into purlins, battens or a deck. In North America common trapezoidal profiles are sold under names such as R-panel and PBR panel; in Europe, Australia and Asia they are usually called trapezoidal or ribbed sheets.

Fastening

Each screw carries a sealing washer or gasket, typically EPDM rubber, that closes the hole. Screw metal must be compatible with the sheet to avoid galvanic corrosion; on aluminium, for example, aluminium or stainless steel fasteners are used rather than ordinary steel.

Advantages

• Low material and labour cost.
• Sheets span between supports and can be used over open framing on agricultural and industrial buildings.
• Fast installation with simple tools.

Limitations

• Every screw is a potential leak point; sunlight hardens washers and thermal cycling loosens screws, with problems typically starting after about 10 to 15 years, so periodic checking and re-screwing is part of maintenance.
• Over-driven or angled screws distort the sheet and damage washers, and fasteners overtightened against thermal movement can fatigue.
• Restricted thermal movement on long sheets can cause noise and waviness.
• Over open framing without a deck or insulation, rain noise is more noticeable than on solid-deck systems.

Comparison with standing seam

Standing seam panels use concealed clips and raised seams, allowing freer movement and fewer penetrations, which is why they are preferred on low slopes and long runs. Through-fastened sheets remain dominant on farm, industrial and low-cost housing roofs worldwide.