Replacing Metal Roof Sheets: Patch or Re-Sheet?

Replacing one or two sheets suits a roof where the damage sits in one spot and everything else is in good order. Typical causes are a dent from a dropped load, a sheet punctured by a tradesperson's boot, or a section lifted by wind where fixings were missing. The job goes quickly when the new sheet has the same profile and gauge as its neighbours and the steelwork below is in good order.

The old sheet is unscrewed, lifted out and the area checked. The new sheet goes down with correct side and end laps, sealed with the tape or sealant the system uses, then screwed through the crests with the matching fasteners. Fixings that are too few, in the wrong place or overtightened are a common cause of leaks, so the details matter more than the sheet.

Check the purlins, the rails and the sheets around. If rust is spreading outward from the damaged sheet, a single swap will not last. Our page on cut edge corrosion explains why rust at the edge of a coated sheet keeps travelling.

There comes a point where patching costs more than it saves. Look for coating that has worn through across the slope, rust at the laps and fixings, sheets that rattle or rock, and leaks that move from one place to another after each repair. If every visit finds a new problem, the roof is telling you the whole covering is tired.

Re-sheeting means stripping the old sheets and fixing new ones over the existing structure, after the purlins have been checked and repaired. It gives a fresh covering with new fixings and new laps, and the chance to improve details such as flashings, ridge pieces and rooflights at the same time. Overcladding, which fixes a new roof over the old one, is another route where the structure can carry it. Our answer on commercial roof coating versus replacement compares those options.

Weigh up the roof's remaining life. Several repairs a year, plus the disruption to the business below, can add up to more than a planned re-sheet. The survey fixes the written price, and the photos show you the roof as it really is.

Metal roof sheets come in many profiles, and few look alike up close. Box profile, trapezoidal and corrugated sheets each have their own crest height, spacing and cover width. Any new sheet needs the same cover width, or the laps will not line up with the neighbours. It also needs a compatible thickness and a coating that will weather in a similar way, though a new sheet will always look brighter for a while.

To identify a profile, measure the pitch of the crests, their height and the width of a single sheet from lap to lap. A sample sheet or a clear measured sketch helps a supplier to confirm it. Some older profiles are no longer made, in which case the choices are reclaimed sheets, a close modern match for a small repair, or re-sheeting the whole bay so the roof is uniform.

Where rooflights sit among the sheets, they must match as well; our answer on industrial roof light replacement shows how. Fixing patterns also differ between sheet makers, so follow the system's own guidance.

Before any work on an older building, ask about asbestos. HSE tells owners of buildings dating from before 2000 to assume asbestos is there. Asbestos cement sheeting is fragile, and the way it is handled matters; it is non-licensed work only if removed without breaking up. If you think sheets may contain asbestos, say so before work begins and leave them alone until they have been checked. Our page on overcladding an asbestos roof goes further.

Access also shapes the job. Working on a profiled metal roof means edge protection, crawler boards and care near rooflights, and large re-sheets may need scaffold, cherry pickers or a crane. If a crane is needed within 6 km of Gatwick, a permit may apply unless the equipment is under 10 m or shielded on all sides.

The price depends on the area, the sheet type, how much needs replacing, the state of the purlins and the access. Ask whether any quote includes VAT. To begin, tell us where the building is, roughly how big the roof is, what sheet type you think it has and whether any earlier reports exist. We then plan how to check the purlins and laps. Our commercial roofing page lists the related work.