Snow Guards and Snow Retention

Smooth metal roofs shed snow readily. That is useful for reducing snow load, but a large slab sliding off at once can injure people, damage vehicles, gutters, lower roofs and plants, or block exits. Snow guards, also called snow retention systems, hold snow on the roof or break it into smaller pieces so it melts or falls gradually.

Types

• Pad or individual guards: small metal or polycarbonate units installed in staggered patterns across the roof.
• Rail or bar systems: continuous pipes, bars or fences running across the slope, held by brackets.
• Panel guards: decorative or plate-type units combining function and appearance.

Products are often powder-coated to match roof colour.

Attachment on metal roofs

• Standing seam: clamps grip the vertical seams with set screws, so guards can be installed without penetrating the panels. Penetrating attachments are avoided on these roofs because they can leak.
• Through-fastened panels: brackets are screwed through the panel into the structure with sealing washers.
• Adhesive mounting: some small guards are bonded on; adhesive-only guards can fail in cold weather.

Design

The number, spacing and pattern of guards depend on roof shape, length of slope (panel run), pitch, ground snow load and what lies below; retention loads are calculated from these factors rather than estimated, and too few guards can shear off in the first large slide. Guards are usually concentrated above entries, walkways, gas meters, gutters and lower roofs. They are not meant to hold all snow indefinitely; the aim is controlled release.

History

Variants of snow-retaining devices have been used for around 300 years in regions with seasonal snowfall, long before modern metal roofs.