Most chimney stacks can be repaired, and repair is where we begin. A rebuild is for the stack that has moved past that point: the joints are open through the full thickness of the wall, the stone or brick is breaking up, or the shaft has shifted so far that new mortar would only be hiding a structural problem. Taking a stack down and building it again sounds drastic, but done carefully it is a controlled job. The old units are numbered, sorted and reused where they are sound, the flues are lined, the lead is renewed and the top is finished so water runs off it. This guide explains how to judge whether your stack needs that, what the work involves step by step, how matching stone or brick is handled on an older Bath house, and what typical UK costs look like. It stays on the rebuild itself. Leaning stacks, flaunching and damp breasts each have their own guide.
When a rebuild beats a repair
Repair works when the fault is confined to the surface. Eroded joints on an otherwise firm stack are a repointing job, and a cracked patch of flaunching can be renewed without touching the shaft. A rebuild becomes the sensible choice when the problem runs through the structure.
- Mortar has washed out of the joints to a depth where the units are no longer held, so a hand pushed against the shaft finds movement.
- Individual stones or bricks are crumbling, flaking or splitting, and replacing them one at a time would mean replacing most of the stack.
- The shaft has a crack that runs across several courses, not along a single joint.
- The stack leans, bows or has rotated, and the cause is in the masonry rather than in the roof timbers below.
- The same stack has been repaired more than once and the faults keep returning.
None of these is an emergency by itself, but they get worse with each winter, because water that reaches open joints freezes and widens them. A stack that is sound enough to survive another year is not always sound enough to survive a storm, so we judge by what we can see and feel on the stack, not by a calendar.
The cheaper repair is not always the better value. Repeated patching on a stack that needs rebuilding can cost more over time than one proper job, and it leaves the same risk standing over the roof and the street. We say clearly when repair will do and price it that way. Where a leaning stack is the reason you are reading this, our guide to leaning chimney stacks sets out which causes are repairable and which point to a rebuild.
How a rebuild is carried out
The job starts before any stone is moved. Scaffold goes up first, because a stack is worked on from all four sides and the crew cannot safely lean from a ladder over a roof edge. Scaffold is a real line on the bill for any stack, and it can match the cost of the masonry work on a small repair. It gets its own entry when we write the price up.
Recording and dismantling
Before taking the stack down, we photograph it from every side and note its height, the number of pots, the shape of the shoulders and the depth of any corbelling. Those records let the rebuilt stack match the original rather than an approximation of it. The stack is then dismantled from the top, course by course. Pots and cowls are lifted off first and set aside, then each unit is removed by hand, cleaned of old mortar and marked so its position is known.
Dismantling continues down to sound masonry. That usually means a course or two beneath the lead at the roof line, but if the damage runs lower we follow it. Stopping too high is the common mistake, because new work built on a weak base fails at the join.
Rebuilding
The sorted units go back in the original bond. Anything cracked or too decayed to bear weight is replaced with a match (more on that below). The mortar is a lime mix suited to the masonry, and each course is bedded fully, not just at the front face. As the stack rises, flue liners are set where the flues need them, the damp-proof course and lead tray are built in at the right height, and the pots are re-bedded in flaunching at the top.
On a normal stack the building itself takes a short run of days, but the lime needs time to take up and the weather decides the pace. We do not push a lime mortar to set in cold or frosty conditions, because frost damage to fresh mortar defeats the purpose of the rebuild.
Matching the stone or brick
A rebuilt stack that looks new on an old roof is a failure of its own kind, so matching is part of the specification, not a finishing touch. On a Bath house the stack is typically built in limestone like the walls, with ashlar faces, moulded cornices or plain copings depending on the age of the house. On other houses within our 30 road miles it may be brick, rubble stone or a mix. Each needs different handling.
The first source of replacement units is the stack itself. Stone that is weathered on one face can sometimes be turned so the sound face shows, and brick that is sound is cleaned and reused. Where new units are needed, they are chosen to match in type, size, bed and colour. Limestone has a grain that must lie the right way: stone set with its bed on edge tends to shed layers in the weather, so a mason lays it the way it formed in the quarry. New stone will look pale next to old, but it weathers in, and a match in type matters more than a match in shade on day one.
The mortar matters just as much. Hard cement mortar around soft limestone or old brick is a well-known cause of damage, because the stone ends up taking the weathering that the joint should take. The Trust that protects Bath buildings, in casework on a Walcot Buildings house in Bath argued for lime in the repairs, and observed that cement had probably worsened the decay of the stack. Lime is softer and more permeable, so moisture leaves through the joint, not through the face of the stone. For more on that problem, see our guide to cement on Bath stone.
If your house is listed, matching is also a legal question. A rebuilt stack changes how the building looks, so raise it with the council planners at B&NES before any work begins. Listed building consent runs separately from planning permission, and doing unapproved work to a listed house can be prosecuted as a criminal offence.
What goes inside the stack
A rebuilt stack is only as good as the parts that cannot be seen once it is finished. Four of them do most of the work.
Flue liners
Where a flue is in use, a liner or the original lining keeps flue gases and condensation away from the masonry. Acidic condensation and sulphates in the products of combustion can attack mortar and stone from the inside, which is one reason old stacks decay from within. If a flue is no longer used, it is capped and ventilated, not simply sealed, so that damp air can leave the chimney.
The damp-proof course and lead tray
A stack is a tall, narrow wall exposed to rain on every face. Where it passes through the roof, a lead tray, which is a sheet of lead formed to sit inside the stack and turn water outward, stops moisture running down the inside of the masonry into the house. It is built in as the stack rises, so it cannot be added afterwards without taking work apart.
Flashings and soakers
A flashing is the lead dressed up the face of the stack and tucked into a joint, so water running down the stack cannot get behind it. Soakers are the little folded lead sheets that run under the roof covering beside the stack. In a rebuild both are renewed as part of the one job, since old lead is rarely worth refitting into new work. A well-detailed lead flashing can last a very long time. MyJobQuote's chimney leadwork guide (September 2026) says correctly installed flashing can last over 80 years.
Flaunching
Flaunching is the sloped crown of mortar that seats each pot and sheds rain. It tends to be the first part to crack, and we cover it in detail in our guide to chimney flaunching.
What a rebuild typically costs
A stack rebuild is the largest item on the chimney price list, and the range is wide because stacks are so different. The guide MyBuilder publishes on chimney work (2026) reports a national spread for a stack rebuild that begins around £2,000 and climbs beyond £10,000 for large or awkward stacks, several times what a typical repair costs. That is a national figure for the whole country, not a price for your house. The price you agree is set once we have inspected the stack, and it covers the scaffold, the masonry, the lead and the clearing away.
What pushes a rebuild towards the upper end? Height is one factor, because a tall stack needs more scaffold, more units and more time. The number of flues and pots is another. Stone costs more than brick to source and to lay, especially where a mason has to cut and dress new pieces. Lime work is slower than cement work. A stack with a cornice or other moulded detail takes longer than a plain one. Access matters too: a stack at the back of a terrace, reached through a neighbouring property or over a tall roof, adds to the scaffold.
Compare the cost with the alternatives honestly. Repointing a stack that needs rebuilding spends money on a short-lived result. Removing the stack is a different decision with its own consequences for the roof and the rooms below, and we cover it in our guide to chimney stack removal. If you are weighing both, the survey will tell you which is realistic for your house.
Insurance, paperwork and what the survey settles
If your stack has been damaged by a storm, the first thing to do is make the area safe, and the second is photograph the damage. An insurer will usually want a storm to meet a wind threshold, and ordinary policies may exclude damage put down to wear and tear. A stack that has decayed over many winters can fall on the wrong side of that line. Photographs and a roofer's report help a claim, though they do not guarantee one, and you deal with the insurer directly. Our guide to chimney repair and insurance sets out what insurers tend to look for, and the wider chimney repairs service page covers the other jobs a stack can need.
Permission depends on the house. A like-for-like rebuild of a stack on an unlisted house is usually a matter of building it correctly, but a stack in a conservation area, or one that will differ in height or look, deserves a call to the planners first. In Bath, about half of the city lies within the conservation area, while the World Heritage Site covers the entire city. If your work could be notifiable under the Building Regulations, ask your building control body or a registered building control approver before it starts.
The survey is where those questions become answers. We climb up to inspect the stack at close range as well as from below, check the flashings, the flaunching and the state of the joints, and take pictures of your own stack for you to look over. You then get a fixed price in writing that names what is being taken down, what is being reused, the mortar, the lead and the scaffold. If repair would do, we price repair. If the stack needs to come down, we show you why.
On completion we clear the roof and ground and carry the waste off, and the workmanship carries our 10-year written guarantee.