The short answer
Commercial gutter lining is a new waterproof layer applied inside an existing gutter, usually a box, parapet or valley gutter on an industrial or commercial building. The old channel is cleaned and prepared, then a liquid-applied coating, a sheet membrane such as EPDM, or a built-up layer is laid into it and turned up the sides and over the outlets. It seals a leaking gutter without full replacement, but only where the gutter structure and its fall are sound.
Where lining is used
Most large commercial roofs do not drain over the edge into a half-round gutter. Water runs into a channel set between two roof slopes, behind a parapet wall or inside the eaves of a portal-framed shed, and then leaves through outlets and downpipes. These are valley, parapet and box gutters. A box gutter is a flat-bottomed channel with vertical sides, and a valley gutter sits where two sloping roofs meet. They carry a great deal of water from a large roof area into one narrow channel, and they are also the first place a leak shows up inside the building, because the water is already sitting where the walls and the ceiling meet.
Older gutters were made from lead, zinc, asphalt or galvanised steel. After many winters the joints open, the metal corrodes or the coating cracks, and the leak starts. Lining deals with exactly this: the channel is the right shape and in the right place, but its skin has failed.
The systems that go inside
There are three main routes. A liquid-applied lining is a resin or polyurethane coating brushed or rolled into the cleaned gutter, often with a reinforcing fleece in the corners and at joints. It adheres to most substrates, copes with awkward shapes and has no seams to leak, which is why it is popular for gutters with many outlets and angles. A single-ply sheet lining, usually EPDM rubber, is cut and bonded to fit, with a few welded or taped joints. It suits long straight runs. A built-up lining, such as bitumen felt layers or asphalt, is the traditional choice and is still specified for some buildings. Compare the membrane families in our guide to commercial flat roof systems, and see liquid coatings for commercial roofs for where coatings suit.
Whichever system is used, the lining has to run up the sides, tuck under the roof covering at each edge and seal around each outlet. Most failures after lining happen at those details, not in the open bottom of the channel.
What has to be right before a lining goes in
Lining is a cover-up, so what lies under it matters. The surface is cleaned back to sound material: loose paint, rust, moss, silt and old failed coating all come out. Rusted steel is treated, holes are patched and any soft boards or rotted timber in the base are replaced. The fall matters too. A gutter that holds water along its length will pond, and a lining over a ponding gutter fails earlier than one that drains. If the channel has no fall at all, the answer is to rebuild it, often with tapered boards, and not to line it. Our page on tapered insulation shows how a slope is built in.
Outlets and overflows deserve attention. Undersized outlets cause overflow into the building, and a lining does not fix capacity. If the roof sheds more water than the gutter can pass in a storm, a larger outlet or an extra overflow may be needed.
Lining or rebuilding
Cost drivers are plain. The length of the gutter, the number of outlets, the state of the base and the access needed to reach it all move the price. Sealing a short parapet gutter with a coating is a small job, while a long valley gutter with a dozen outlets and rotten boards is a different one. That is why we will not quote a figure from a photo, and why the survey comes first.
Lining wins when the structure is sound and disruption must be low. It can be done from the roof, often without scaffold on the elevations or any break in business use, and it costs far less than replacing the gutter. Rebuilding wins when the base has rotted, the fall is wrong, or the gutter is too small. Both are legitimate. A short, honest survey tells you which applies.
Lined gutters still need looking after. Silt, leaves and bird nests block outlets, and a quick check in autumn and spring avoids most trouble. Read our page on planned maintenance for commercial roofs for how that fits into a service routine.
We begin with a free survey and photograph the gutter, its joints and its outlets, so you can see where the water is getting in. If lining will do, we say so and give a fixed written quote. If the gutter needs rebuilding, we explain why. The wider range of work is on our commercial roofing in Basingstoke page.
Every roof is different. A free survey with photos settles it for yours.
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