How sliding snow bends a panel
A slab of snow on metal slides as one piece, and the eave takes the full force.
Snow on a metal roof can bond to the panel in the cold and then release all at once when the sun comes out. The slab slides down the slope and drops over the eave, and the first panels catch its weight. The panels bend where their fixing is weakest, and the bend is often a shallow dent that is easy to miss from the ground.
The crew reads the bend pattern across the eave. A line of bent panels at the same height points to a slab that came down together, and it shows the snow guard position needed to stop the next one.
- Slab releases all at once
- First panels catch the weight
- Bend line shows slab position
Fasteners, washers and the rattle
A fastener that has lost its washer lets water in and lets the panel move.
Metal roof fasteners carry a sealing washer that stops water at the hole. Cold weather and wind work the washer until it cracks, and the fastener then leaks and lets the panel move. The movement is what makes the rattle that owners notice in a wind.
The repair replaces the washer or the whole fastener, and the panel around each one is checked for a gap. A fastener that has been over-driven and dimpled the panel is also replaced, because the dimple holds water.
- Cracked washer lets water and movement in
- Replace washer or fastener
- Over-driven fasteners replaced
Seams and the panel lap
A seam that has opened at a lap is re-formed to the manufacturer method, not sealed over.
A standing seam or a lapped seam relies on its profile to shed water. When the seam opens, sealant alone is a short fix. The crew checks the seam for the profile and re-forms it where the metal allows, then seals the lap as a secondary measure.
Where the seam cannot be re-formed, the panel is replaced. The replacement is set to the lap of the panels on either side so the water still runs over the joint.
- Seam re-formed to profile
- Sealant as a secondary seal
- Panel replaced where seam cannot be re-formed
Trim, the drip edge and the gutter
The trim at the eave carries the panel edge, and bent trim lets wind and snow in under the metal.
Eave trim and the drip edge hold the metal panel to the fascia. Trim that has been bent by snow or pulled by wind leaves a gap that lets water run behind the panel and the wind lift the edge. The trim is re-set and fixed into the fascia before the panel is closed.
The gutter at the eave is checked for the same movement. A metal roof sheds snow onto the gutter in a single slab, and the gutter and its brackets are checked for the slide.
- Eave trim re-set and fixed
- Gap behind panel edge closed
- Gutter and brackets checked for slide
Expansion and the cold
Metal moves with the cold, and the fixings must allow for it.
Metal expands and contracts across a season more than shingles do. A fastener driven too tight can buckle the panel in the cold, and one left too loose can lift in the wind. The crew sets each fastener to the depth the manufacturer and the panel profile require.
A panel that has been bent by a previous repair may not move freely any longer, and the crew checks the panel for that before it adds more fixings.
- Fasteners set to panel depth
- Tight fixings buckle panels in cold
- Previous repairs checked for free movement
Clearance at the eave and the ridge
A metal panel needs room to move, and a fixing set against the edge of a panel can crack it.
A metal panel expands at its length, and the fixings at the ends must allow the movement. A fixing set too close to the panel edge or against the flange can crack the metal at the first cold snap. The crew checks the clearance at each fixing before it tightens it down.
The ridge is checked the same way. A ridge cap that is fixed hard to the panels at both sides cannot move with the metal, and it bends or splits in the cold.
- Movement allowed at panel ends
- Fixings clear of the panel edge
- Ridge cap free to move
Panel profiles and replacement stock
A replacement panel has to match the profile of the one it replaces, or it will not seat.
Metal panels come in profiles, and a replacement that does not match the profile will not lap properly with the panels around it. The crew measures the profile on the roof and records the match, because a replacement that is off by a rib leaves a gap that water and snow will find.
Where the panel line is old and no match is available, the crew says so and records the nearest profile. The owner is told the difference and can decide whether to replace a whole run for a clean line.
- Profile measured on the roof
- Match recorded on the job
- Owner told of nearest profile
Corrosion and the cut edge
A cut or scratched edge in a metal panel can start corrosion if it is left bare.
When a panel is cut to fit or scratched during a repair, the bare edge can begin to corrode, especially at the eave where meltwater stays. The crew checks any cut edge for coating and touches up the exposed metal with a suitable coating before the panel is set.
Corrosion at the eave is recorded on the job, and any panel that shows it is noted for replacement at the next repair cycle rather than left for the owner to discover.
- Cut edges checked for coating
- Exposed metal touched up
- Eave corrosion recorded for next cycle
The owner's checks between visits
The owner can see most metal roof damage from the ground after a sliding snowfall or a wind.
After a sliding snowfall the owner can look at the eave for bent panels and at the gutter for a dent or a sag. After a wind, the owner can look for a panel that has lifted at the edge or a fastener head that stands proud. Each finding is reported with a photograph taken from the ground.
The crew will check any reported finding on its next visit, and it does not expect the owner to climb onto the roof.
- Eave and gutter checked after sliding snow
- Lifted panels and proud fasteners noted
- Findings reported with ground photographs
