Stand on a Georgian street in Bath and look up. The roof, if you can see it at all, sits well back, and the front of the house ends in a low stone wall. The parapet is that wall. Behind it, along the whole frontage, is a gutter lined in lead, and it carries every drop that falls on the roof slope behind. Nobody looks at it from one year to the next. It is also one of the most exposed details on the building: long, shallow, reliant on its slope and its outlets, and made of a metal that moves with the weather. When it leaks, nothing drips from a gutter. The water soaks the stone beneath the coping and the rooms below it. Knowing how the gutter is built, how it fails and what a proper relining involves puts you in a better position to judge any quote for the work.
Why the gutter sits behind the parapet
A parapet is a low wall carried up above the eaves line. On a Georgian terrace the designer wanted a flat, uninterrupted stone front, with no overhanging gutter and no visible slope, so the roof was set back and the wall was lifted to hide it. The cost of that tidy front is that rainwater has nowhere to fall away from the building. It has to be collected in a channel running behind the wall, and led out to a downpipe at the end of the run or through a hole in the parapet itself.
That channel is the parapet gutter. It runs the length of the roof slope it serves, and the roof slope drains into it. On a wide frontage it may serve a large area of roof, which is why the lead in it is thick, the sheets are wide and the outlets matter so much. The gutter is typically bounded on one side by the parapet wall and on the other by the foot of the roof slope, so it has a built-in upstand on the stone side and a lap of slate or tile on the other.
The Bath Preservation Trust's published casework gives a flavour of how these roofs read. In a comment on Lambridge Place, the Trust contrasted a mansard, which shows from the street, with a plain pitched roof that sits out of sight. Another, on a Grade I square in the city, saw it back fresh lead in the valley gutters. These are single cases and not a rule about the city, yet they show how much is tucked away behind the stone.
One consequence is that a parapet gutter is almost never inspected. A top-floor ceiling stain is often the first sign, and by then the water has been finding its way in for a while. If you own a house of this kind, find out where the gutter and its outlet are, and ask for it to be looked at when the roof is surveyed. Our wider guide to box gutters covers the related channel that sits between two roofs rather than behind a wall.
How a parapet gutter is built
The construction is layered, and each layer has a job. At the bottom are the bearers, the timbers laid across the roof structure that set the shape of the gutter bed. On them sit boards, usually planed softwood or exterior plywood, laid so that the bed falls steadily towards the outlet. On top of the boards goes a separating layer, so the lead is not abraded by the timber as it expands and contracts, and then the lead itself.
Falls decide whether the gutter works. For flat surfaces in general, BS 6229:2018, as quoted in manufacturers' guidance, recommends designing to 1:40 so that finished falls come out at about 1:80 once tolerances are taken up. A parapet gutter that was built flat, or that has sagged since, holds standing water in the middle of its run. Standing water speeds the wear on lead, finds any weak seam and puts a load on the boards.
The lead is laid in lengths, joined across the gutter by steps called drips. A drip is a raised step in the gutter bed, formed in the boards, that lets each sheet end and the next begin a little lower, so water runs over the joint and not into it. Along the sides, the lead is turned up the parapet wall as a flashing and tucked into a joint cut in the stone, and at the roof edge it turns up under the slates or tiles. The corners are folded, not cut, wherever possible, because a cut corner is a weak one.
The outlet is the last link. It may be a pipe through the parapet, a rainwater head that discharges into a downpipe, or a sump, which is a small lead-lined box that gives the water somewhere to gather before it enters the pipe. Many gutters also have an overflow, a lower opening through the parapet that lets water out visibly if the main outlet is blocked, so the overflow spills on the street, not into the house. If your gutter has lost its overflow, or it has been blocked with mortar, the safety margin has gone.
Where and why they fail
Lead is long-lived. The cost guides we cite give flashings a life of over 80 years, and lead flat roofs 50 to 100 years, when properly installed. A parapet gutter that fails in a few years has usually been let down by something other than the age of the metal. These are the common causes.
Splits at drips and laps
Lead swells in warm weather and shrinks again in cold. If a sheet is cut over-long or pinned hard, it cannot move freely, so the metal stretches and cracks at a fold or a drip. The crack is often a hairline that lets in water slowly. Our page on repairing split lead deals with the repair side, and the same movement is the reason long runs are broken up by drips.
Blocked outlets
Leaves, moss, a dead bird and slate fragments settle in a gutter bed and make their way to the outlet. Once it is blocked, water rises behind the parapet, past the upstand and into the wall head. Clearing the outlet twice a year is the cheapest piece of maintenance a house of this type can have, and our guide to clearing parapet gutters sets out how it is done safely.
Defects below the lead
Rotted boards and bearers let the bed dip and the lead tear. Dry rot and wet rot both start in the roof timbers when a slow leak goes unnoticed. A relining that ignores them is a short-lived one.
Problems in the stone and the flaunching
Open joints in the parapet, a loose coping and failed pointing all let water in beside the flashing, and the symptom looks like a lead failure when it is not. Cement pointing is a repeat offender on older masonry, a point the Bath Preservation Trust raised over a chimney stack at Walcot Buildings.
Finding which of these is at fault is the point of the survey. We lift or look under the lead where we need to, and photograph what we find on your roof.
How a leaking parapet gutter shows itself
The signs are rarely dramatic at first. They tend to appear on the top floor and the party wall, and they get worse in prolonged rain. The most reliable indications are these.
- A brown stain on a top-floor ceiling or along the cornice, close to the front wall.
- Damp or flaking plaster on the inside of the front wall at the top of the house.
- Stains or green growth running down the face of the parapet stonework.
- Water spilling out of the overflow, or pouring from the parapet when it rains hard.
- Rust or damp on the roof timbers, if you can see them from the loft.
Because the leak can enter a long way from where it shows, the stain is not a map. Water follows timbers, runs along a rafter, drops from a joint and appears two metres away. Plugging the nearest-looking spot rarely answers the question. We trace it by following the water uphill, from the ceiling to the gutter.
Some owners assume a stain after storms means a slipped slate. It can, but a parapet gutter is just as likely, since a heavy fall of rain tests its capacity in a way a mild day does not. If the stain returns after every storm, the gutter's size, falls or outlet may be wrong for the area it drains, not just damaged. Our guide to the causes of a leaking parapet gutter follows the symptoms in more detail.
Repair can be enough where the damage is local: a split at one drip, a lifted flashing, a blocked outlet. We repair where repair works. Where the lead is cracked along the run, the falls are wrong or the boards are rotten, patching returns you to the same problem, and relining is the answer.
Relining step by step
Relining means stripping the old gutter back to the structure and rebuilding it. The sequence is much the same on every job, though the details change with the building.
- Access and protection. Scaffold or a platform goes up, and the roof beside the gutter is protected from falling debris and rain. On a street-front parapet this step alone can take up a large share of the price.
- Strip. The old lead is lifted, the underlay removed and the boards and bearers inspected. Anything rotten is cut out.
- Re-form the bed. The bearers are adjusted and new boards laid to correct falls, with drips set at suitable intervals.
- Underlay and lead. A separating layer goes down, then the lead, cut to length and dressed into the bed and up the sides. Joints follow the pattern of the gutter, and corners are folded.
- Outlets and overflow. The outlet is checked or renewed, the sump rebuilt if there is one, and the overflow is confirmed to be clear.
- Upstands and stonework. Flashings are wedged into the parapet stone and the joint repointed in lime mortar, and the roof covering is re-lapped over the edge.
Supplier data from a cast lead brochure shows the typical use of the heavier codes: code 5 and 6 for flashings and parapet gutters, and codes 7 and 8 for gutters that take a heavier load. We specify the code for each part and name it in the quote, and the price follows the survey, in writing. Ask for the falls and the drip positions to be marked on the quote as well, so you can check them against the finished gutter. Our guide to leadwork costs shows the ranges that exist for this kind of work, and points out where no reliable figure exists.
Listed houses, consent and the stonework
Many Bath houses with parapet gutters are listed. Bath has some 5,000 listed buildings, set in a city that is wholly a World Heritage Site. When your house is one of them, work that changes its character or the roof materials calls for consent from B&NES Council. Listed building consent is distinct from planning permission, and skipping it is a criminal matter. Talk to B&NES before anything starts.
Relining a gutter in lead, like for like, is repair in the ordinary sense and often sits within what a listed building owner can do, but whether consent is needed turns on how much is being done and on the listing itself. If you are changing the lead for another material, altering the depth or the falls in a way that shows, or disturbing historic fabric, ask first. The conservation team at B&NES is the place to ask, and we explain the position on your own house at survey.
Building Regulations raise a different point. The Planning Portal says approval is not normally needed for repair or re-covering that touches under 25 per cent of the building envelope and under 50 per cent of the roof. A gutter relining on its own usually sits below that, but the answer depends on what else is being done. We confirm it with your building control body where it applies.
The stone matters as much as the lead. Cement mortar on old stonework traps moisture and can damage the stone, and lime mortar is the usual replacement. If parapet joints need work, the mason and the leadworker should plan the sequence together, because a lead flashing set into bad pointing will not stay watertight. For the other main hidden gutter on older roofs, the box gutter guide explains the construction, and our lead roofing page describes the service in full.