Question answered
Industrial gutter lining
The short answer
Industrial gutter lining means fitting a new waterproof layer inside an existing valley or box gutter, so the old steel or lead no longer has to hold the water. It suits a gutter whose structure is sound but whose surface leaks. A gutter that is rotten, sagging or too small needs repair or replacement first, and the outlets must be able to clear the flow.
Valley and box gutters on industrial units fail quietly and flood the building when they do. A liner can renew a sound gutter without stripping the roof, provided the gutter is worth keeping.
Why valley and box gutters fail
A valley gutter runs along the join between two roof slopes, and a box gutter is a rectangular channel, often tucked in beside a parapet wall or sandwiched between two roofs. Both collect the water from a large area of roof and carry it to a few outlets, so they work much harder than a gutter on a house. Leaves, moss, silt and bird debris build up, outlets block, and the water stands.
Standing water finds every weakness. Steel rusts through at joints and fixings, lead splits where it has crept, and old sealant and bitumen crack with age and temperature. The leak usually shows inside as a stain beneath the gutter line or a steady drip in a storm, and in a unit with stock racked below it can ruin goods before anyone has traced the cause. Because the gutter is hidden, the first sign is often damage rather than a visible fault. Our page on replacing a damaged roof sheet deals with the sheets alongside the gutter, which often need attention at the same time.
What a lining involves
A liner is a continuous waterproof layer laid inside the gutter. It is usually a single-ply membrane, for example EPDM, a synthetic rubber sheet, or a glass-reinforced plastic skin known as GRP laid over the prepared surface. Published guides put EPDM at 20 to 30 years or more and GRP at 25 to 40 years, as typical ranges and not promises.
The gutter is cleaned and prepared first, with rust treated, loose material removed and the base made even. The liner is then run up the sides and tucked under the roof sheets so that water cannot get behind it, and it is joined or sealed at the outlets. Where a gutter has been patched many times over the years, a lining can finish the job in one continuous piece. The membrane is described further in our guide to single-ply membranes.
Outlets, falls and capacity
A lining only works if the water can leave. Outlets and rainwater pipes are checked for size and condition, and an overflow is added where a blocked outlet would otherwise flood the building from inside. Flat roofs are designed with a fall, and IKO, citing the 2018 edition of BS 6229 (since revised), advises designing for 1:40 so that the finished minimum is 1:80. A gutter that holds a pond cannot be cured by a liner alone, because the pond stays in the new lining.
If the gutter is too small for the roof it serves, a lining makes it watertight but does not make it larger. In that case the outlets are enlarged or the gutter is rebuilt wider. Fall and capacity are among the first questions the survey answers, because they decide whether a lining or a rebuild is the right job for the building in front of us.
When lining is not the answer
Lining is for a gutter with a sound base. If the supporting steelwork has corroded, the timber deck beneath a lead gutter is rotten or the gutter sags under its own weight, a liner would only cover a failing structure. Fix the structure first, or replace the gutter altogether, and make the repair one that lasts rather than one that looks tidy for a season. A timber deck that squelches underfoot, a gutter bottom that rings hollow when tapped or sheet edges that crumble when pressed are all signs that a liner would be covering the wrong problem.
The same goes for a gutter running beneath fragile rooflights or asbestos sheets, where access has to be planned with care; see replacing industrial rooflights for the hazards. A lining is recommended when it properly solves the problem and replacement when it does not, and the reason is explained with pictures of the gutter on your own roof.
Planning the work
Lining is best done in dry weather, because the surface has to be dry and clean for the liner to bond. Access is usually from a platform or cherry picker rather than the roof itself, and the work can often be arranged so that the building keeps trading. Tell us about any nearby deliveries or customer entrances so that the working area can be fenced where it matters.
A survey comes first. Our commercial roof condition survey records the gutter, the outlets and the surrounding sheets in photographs, and our written price follows as one overall sum. The cost depends on the length and width of the gutter, the access and the condition of the base, which is why the quote follows a visit and not a phone call. Our wider commercial roofing service sits behind it.
Gutter lining: two more questions
Can a liner be fitted over a lead box gutter?
Sometimes. The lead and its boards must be sound and the surface prepared, and the liner must be compatible with the material beneath. If the lead has split or the timber deck has rotted, the structure is repaired first. A survey tells you which applies to your gutter.
How often should a valley gutter on a unit be cleared?
Often enough that it never holds water for days. Check after autumn leaf fall, after storms and before winter, and clear a gutter beside trees or a bird roost more often. Clearing from a platform or from the ground is safer than going onto the roof.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.