Most cut edge corrosion we see in Coventry is picked up one of two ways. Either a tenant flags up drips along a wall after heavy rain, or a surveyor spots rust at the sheet ends during a routine check. The first route is more common and usually more expensive. Either way, it pays to understand what’s happening at the edges of a profiled metal roof, why it speeds up, and where the honest line sits between treating the sheets and replacing them.
The first sign is usually a leak
By the time water shows inside your building, the corrosion at the sheet ends has usually been working away for years. Coventry’s commercial buildings lean heavily on profiled steel: think of the mid-century manufacturing and engineering units from the city’s motor industry heyday, plus the newer logistics and trade-counter sheds dotted around the ring road and beyond. Most of those roofs were laid with plastisol-coated sheets, and every single one of those sheets has cut edges sitting in the wettest spots on the roof.
The pattern of the leak is the giveaway. If you’re seeing drips appearing in lines, following the laps or the eaves rather than a random spot, that points to corroded sheet ends. It’s not just a single failed fixing or flashing. If that matches what you’re seeing in your building, assume the corrosion is well established and get the roof surveyed before the next downpour.
How corrosion takes hold at a cut edge
The coating on a plastisol sheet protects the faces, but not the cut. Where sheets are cut to length, you’ve got bare steel exposed at end laps and gutter edges. Water sits there, the steel oxidises, and rust creeps back under the coating. We call that underfilm corrosion. The coating peels away from the edge, more steel gets exposed, and the cycle just feeds itself.
Laps make it worse. Moisture drawn between overlapping sheets can’t evaporate, so the steel inside the lap corrodes away out of sight. A roof can look perfectly fine from the ridge, while the lap zones are quietly thinning and weakening.
Treat the edges now, or replace sheets later
The economics are simple. If we treat the edges while the steel is still sound, that means cleaning back the corrosion, priming with the right corrosion-inhibiting products, and sealing the laps and edges with a flexible system. It’s a repair measured in days, done from the outside, with your building staying in use throughout.
Delay changes the maths completely. Once those sheet ends perforate, you’re into strip-and-replace. That means access costs, internal protection, and disruption to whatever your building does. Few maintenance decisions on a metal roof have a clearer payoff for acting early than this one.
The honest cases where we say no
Some roofs are too far gone, and we’ll tell you when yours is one of them. If we see holes right through the sheet ends, lap corrosion across most of the roof area, or steel so thinned it flexes underfoot, those aren’t candidates for treatment. Coating over that is just a short-lived cosmetic fix, and we won’t offer it. In those cases, our survey report will recommend replacement or over-roofing, with our reasoning and photographs, so you can make the decision with all the facts in front of you.
What we record before quoting
We’re survey-led. We don’t quote anything from the ground or from photographs alone. Up on your Coventry roof, we record:
- How much edge corrosion there is at the gutters, end laps, and side laps.
- Whether the steel at the worst points is still sound, or if it’s perforated.
- The condition of the factory coating across the sheet faces.
- Gutter condition, because failed gutters are a big driver of edge corrosion.
- Fixings, flashings, and rooflights that affect the same scope of work we’re looking at.
If the wider coating is chalking or fading, we’ll tell you if a full roof coating alongside the edge work makes better sense than two separate visits years apart. We’re based in the South East but work across the UK. Coventry is a straightforward area for us to survey. Get in touch with the building address and a description of what you’re seeing.
