A polycarbonate roof over a patio or carport takes hail the same way a shingle does, but the damage often shows up as a small crack at a screw hole rather than a dent you can see from the yard. If your storm year left you with a clear panel roof, the surface may look fine from the back door while the fasteners holding each sheet have started to work loose. The check is quick, and it is worth doing before the first hard freeze, when a panel that has already cracked can split along the line.
Why the screw holes fail first
Polycarbonate sheets expand and contract more than most homeowners expect. In a St. Louis summer a sheet in full sun can run hot enough to move noticeably along its length, and in winter the same sheet shrinks as the air drops below freezing. Each sheet is held down by screws or clips through pre-drilled holes, and those holes have to allow for that movement. Hail hitting the sheet can bend the panel around a fastener, enlarge the hole, or chip the plastic right at the edge of the washer. Once the hole is oversized, the screw no longer clamps the sheet the way it was set, and the sheet can start to rattle or shift.
That is why the first thing to inspect is the fastener, not the middle of the panel. A hailstone big enough to crack a sheet can leave a dent that looks like a bruise on a window, but the crack more often starts at the edge of a screw head or the rim of the hole, where the plastic is already under stress.
Walk the fasteners before the glazing
Start at the low end of the run, where the panels are easiest to reach and where wind-blown debris collects. Look at every screw head. Note any screw that stands proud of the washer, any washer that has cupped or cracked, and any screw that turns easily when you press it. A screw that spins without tightening has lost its grip, usually because the hole has stretched. Do not tighten a stripped screw into an oversized hole, because the plastic will crack under the extra torque. Mark the fastener with a piece of painter's tape and write its location on the tape, so the same screw can be checked after the next storm.
Next look at the sheet itself, in good light. Hold the sheet at an angle to the sun and move your head slowly. Hairline cracks show a white or silvery line when the light catches them. Dents show as shallow shadows. Stress cracks that run out from a fastener are the ones that matter, because they tell you the hole is already the weak point.
The sheet edges and the cap channel
Polycarbonate panels are usually closed at the ends with a channel or a foam closure strip that keeps insects and water out of the hollow ribs. Hail that hits the edge of a sheet can crush that closure, leaving the ribs open. In winter, water that sits in an open rib can freeze and split the sheet from the inside. Look at each end of each run. Note whether the closure strip is still seated, whether any rib is crushed flat, and whether there is water staining or a cloudy line along the inside of the sheet.
The cap channel at the ridge or the high edge of a run deserves the same attention. If a cap has lifted or the sealant has pulled away, the next wind-driven rain will find a path into the ribs. A patio cover that drips at one end of a run often has a failed cap channel at the high end, not a hole in the sheet.
What the freeze and thaw does next
St. Louis winters move water in and out of small cracks more than they move it through big ones. A crack that you could ignore in July can open in January when a thaw follows a freeze, because the ice inside the crack pushes outward and the sheet has less give. Check the panels again after the first hard freeze, and again after the first thaw. If you see a crack that has grown, or a screw that has backed out, the panel needs attention before the next cold snap rather than after it.
Sun exposure matters too. The side of a run facing south or west takes the heaviest sun in summer and the most ultraviolet light across the year. Many polycarbonate sheets carry a UV-protective coating on one face, and a hail impact that breaks through that coating can let the plastic yellow and crack faster on that side. A sheet that looks clear on the north side but has a dull, chalky look on the sun side has been weakened by the sun, and a hail hit in that area is worth recording separately.
What to photograph before anyone touches the panels
Photograph the run from a fixed position, once from each end and once from the middle, so the locations are easy to match later. Then photograph each damaged fastener or sheet with a coin or a tape measure in the frame for scale. Keep the original image files, not screenshots, and note the date each photo was taken. If you can, record a short walk-through video along the length of the run while moving slowly, because a video can show a rattle or a shift that a still photo cannot.
Write down what you saw in plain words. "Screw at the third purlin from the left end, washer cracked, screw turns freely" is more useful than "bad panel." A written list with the photos gives a roofer, or anyone else reading the file, something they can check against the panels.
What to ask a roofer or contractor
When you call a contractor to look at a patio cover or carport, ask them to walk the fasteners and the sheet edges the same way, and ask them to put what they find in writing. A written scope should list each damaged panel, each failed fastener, each closure or cap that needs replacing, and the measurements or photos that support it. Ask whether the work includes replacing the sheets with the same profile and thickness, or whether a different profile is being quoted. A panel that does not match the rest of the run will look different in color and sheen, and that should be on paper before the work starts.
Ask how the replacement sheets will be fastened. Ask whether the screws will be new, and whether the washers are rated for the sheet type. Ask whether the cap channel and closure strips are included in the price or priced separately. If the contractor says a repair is just a matter of tightening, ask them to show you the hole and explain why the screw will hold.
Keys Roofing documents damage and puts a written scope with photos and measurements in the homeowner's hands. If your polycarbonate cover is part of a storm claim, that claim belongs to you. Missouri law (RSMo 407.725) bars a roofing contractor from representing or negotiating a homeowner's insurance claim, so the contractor can document the damage and attend the work while you deal with your own insurer directly. Keep the photo file and the written scope together, and bring them to any conversation with your insurer.
A short checklist for the next walk
Before the next hard freeze, walk the run once from end to end. Check every screw and washer, look for cracks in the sheet with the sun behind you, check the closure strips and the cap channels, and photograph anything that has changed since the last walk. Write the date on each photo. If you find a panel that has cracked, a screw that has backed out, or a closure that has pulled loose, get it looked at before the next storm, because the next front can bring hail back to the same spot.