How a Deck Collapsed Under Ice — A Cautionary Design Story

Not every deck failure comes from a weak joist or a rotted post — sometimes it comes from a clever-looking design decision that quietly overloads a component never meant to carry that kind of weight.

One case involved polycarbonate roofing clips — a genuinely strong material, since polycarbonate is one of the toughest common plastics available. The problem is that every material has a maximum usable load, and most plastics also degrade with UV exposure over time, becoming more brittle year over year. In this case, the clips holding the polycarbonate panels in place were designed for a different job entirely: they were rated to hold snow on steel or aluminum roofing, not to carry the load of the panel itself under sustained ice buildup.

Here’s the mechanism that made it fail: those snow-retention clips work exactly as intended, holding snow on the roof surface rather than letting it slide off — which sounds safe, until that retained snow sits through a prolonged cold spell and gradually turns to ice. Ice accumulates over months, and the load eventually exceeds what the plastic clips can bear. Multiple clips failed at once — a failure mode more typical of plastic components than metal ones, which tend to fail more gradually and individually rather than simultaneously.

The broader lesson: components borrowed from one application (holding snow on a roof) and repurposed for another (structural support under a polycarbonate deck cover) need to be re-evaluated for the actual loads and exposure they’ll face in their new role — not assumed to be strong enough just because they’re rated strong for something else.