After the Hailstorm: Glass Gone, Steel Dented, PC Still There

Oct 30, 2026

Three materials under hail

Material	Typical outcome	Consequence
Glass	Shatters and falls	Safety hazard, immediate replacement
Coated steel	Dents, coating damaged	Ponding in dents, corrosion start
GRP roof light	Cracks, perforates	Leaks, transmission loss
PC roof light	Dents, local whitening	Mostly stays in service

The difference is where the energy goes. Glass and GRP cannot deform, so energy is released by fracture; PC deforms, absorbs and recovers.

Four variables that decide the outcome

Thickness — thicker resists more, but not linearly, and 8 mm multiwall and 3 mm solid fail by different mechanisms, so thickness alone is not comparable.

Ageing — the most overlooked factor. Without a UV layer, the surface degrades after three to five years outdoors and toughness falls; the same hail that bounced off a new panel may perforate an aged one. Hail resistance describes the panel's condition today, not at dispatch.

Support spacing — the panel spans between purlins. The wider the span, the deeper it deflects and the more likely it cracks around fixings.

Hail size and velocity — energy scales steeply with diameter; a 50 mm stone carries more than fifteen times the energy of a 20 mm one. Any hail claim must state its test conditions.

What to demand

Ask whether there is a falling-ball or ice-ball impact report, and for the ball diameter, drop height and panel thickness tested; whether the data is pre- or post-ageing; and what impact value applies at the purlin spacing they recommend. Without test conditions, "hail resistant" means nothing.

Where it matters most

Greenhouses and propagation houses, where one storm can destroy a season and glass roofs are high risk in hail belts; carports, where vehicles take the damage and shattered glass falls on them; agricultural parks and orchard covers; and upland or high-convection inland regions.

It matters least for low-level urban canopies in areas with little hail.

After the storm

Inspect around fixings first, since cracks usually start at holes. Small dents need no replacement, but any perforation or propagating crack does. Log each hail event and the damage location — it becomes the basis for choosing thickness on the next project.

FAQ

Can hail perforate PC? In extremes — large stones, high velocity, aged sheet — yes. Specify with a margin based on local hail history rather than best-case assumptions.

Solid or multiwall for hail? At equal thickness solid usually resists more, at higher weight and cost. Multwall's advantage is insulation; hail performance depends on the specific structure.

Does a dent affect service? Not structurally, and it remains waterproof, but transmission and appearance suffer locally. Extensive denting justifies a warranty assessment.