What is an industrial gutter lining?

Large industrial roofs usually drain into gutters that sit between two roof slopes or behind a parapet wall, rather than into the small half-round gutters of a house. These box, parapet and valley gutters carry a great deal of water from a big roof area, and when one leaks the water goes straight into the building, onto stock, machinery and floors.

A lining is a new waterproof skin laid inside that gutter. It can be a sheet of membrane adhered in place, a liquid coating built up in layers, or a glass-fibre laminate, known as GRP. The choice depends on the gutter's shape, what it is made of, how much it moves with temperature and what is already stuck to it.

The idea is simple. Instead of stripping the gutter out and rebuilding it, the old one becomes the shape and the new skin becomes the waterproofing. Our commercial roofing page shows where gutter work sits among the other jobs.

Long runs of metal gutter expand and contract with the weather, and the joints are where they usually give up. A sealant that was fine on installation splits, a rivet works loose, or a lap opens a hairline. Leaves, moss and general debris then gather at outlets and hold water against the weak joint for days at a time.

Rust is the other cause. Steel gutters corrode from the inside once the coating wears through, particularly along the bottom where water stands. Lead and zinc linings on older buildings suffer in a different way, cracking where they have been stretched by movement over many seasons.

Where the existing gutters are asbestos cement, HSE lists rainwater goods among the asbestos cement products, which changes how any work is done. Our guide to the asbestos cement industrial roof explains the position, and the material is confirmed before anything is cut.

A lining only holds if it sticks to something sound. The gutter is cleared of silt and plant growth, loose rust and flaking paint are removed back to firm material, holes are patched and joints are made good. Then the surface is cleaned and primed to suit the lining that is going on.

The gutter must also fall to its outlets. BS 6229:2025 keeps a minimum finished fall of 1:80 for internal gutters among other roof areas, and a lining laid in a gutter that holds a pond will age early and may fail at the lowest point. If the falls are wrong, the gutter either needs reforming or the lining needs to be paired with a local build-up.

Outlets are checked at the same time, since a blocked or undersized outlet will overload any lining. Our answer on ponding on a commercial flat roof covers what standing water does to a roof surface, and gutters behave in much the same way.

A lining suits a gutter whose structure is still good: the base is firm, the sides are straight, the supports are sound and the damage is in the waterproofing. It avoids scaffold for removal, avoids damage to the roof edge and keeps the building working. The gutter keeps its size, which can be a limit if it was undersized to begin with.

Replacement is the better call when the metal has gone through in several places, the brackets are rotten or the gutter cannot cope with the roof it serves. A lining on a failing structure buys a little time and then lets you down.

We photograph the gutter along its length and give you a plain verdict: line it, line part of it, or replace it. Our repair or replace guide for commercial roofs sets out the usual tests, and the written quote that comes after the survey covers whichever of the three we advise.

A lined gutter is only as good as its drainage. Outlets should be big enough, free to run and easy to reach for clearing. A visible overflow route, such as a weir or an overflow pipe through the parapet, tells you something is blocked before water finds its way into the building.

Upkeep is simple but regular. Clear the gutter after storms, keep contractors from walking in it, and keep a record of what was fitted and when. If a lining is damaged by a dropped ladder or a boot heel, a small repair is far easier than a big one, and the sooner it is seen the smaller it stays.

Gutter checks fit naturally into a planned visit. Our page on commercial roof maintenance shows what a routine inspection looks at, and gutters sit near the top of that list, because a blocked outlet turns a minor defect into a wet building faster than anything else.