A chimney stack is the part of the chimney that stands above the roof. Wind and rain reach it from every side, and it is built from small units bedded in mortar that was never meant to last for ever. Repointing and flashing repairs deal with most faults. A rebuild is the job for a stack whose structure has given up: bricks or stones that move when touched, a lean that has set in, a crack that runs through the courses, or a top that has come away from the shaft.
This page covers the rebuild itself. It explains the signs that point to rebuilding, how a stack is taken down and put back, how bricks and stone are matched, what the scaffold has to do, and what to check on consent. Prices for all chimney work are in our chimney repair costs guide. Two related jobs have their own pages: leaning chimneys and chimney removal. The wider service is on our chimney repairs page.
The point where a stack goes from repair to rebuild
Repair means keeping the existing masonry and putting right what has failed around it. Rebuilding means taking some or all of that masonry down and building it again. The line between the two is drawn by what the masonry can still do. Joints eaten back by weather with sound bricks behind them are a repointing job. Bricks that have crumbled to powder on their faces, or stone that has split along its beds, cannot be saved by new mortar, because there is nothing firm for the mortar to grip.
Signs we treat as rebuild signs
When we survey a stack from the scaffold or by close photography, a few findings move the conversation towards rebuilding:
- Units that rock or lift out by hand, so the shaft is no longer acting as one piece.
- A visible lean, or a step in the line of the shaft where one section has slid on another.
- Cracks that run through bricks and joints together, rather than following the joints alone.
- A top section that moves independently of the shaft below it.
- Brick faces that have flaked away across a whole face of the stack, not just at a few corners.
None of these on its own settles the question. A lean, for example, has several causes, and our guide to why chimneys lean sets out how we tell a stable old tilt from a stack that is still moving.
Partial or full
Many rebuilds are partial. If the lower shaft is sound and only the top few courses have failed, we take down to the sound masonry and build back up from there. The test is simple: we dismantle until the masonry is firm, and we stop. That keeps the cost down and keeps as much of the original stack as possible, which matters on an older house.
Taking a stack down and building it back, stage by stage
A rebuild is a sequence, and the order protects both the roof and the people below.
Recording before dismantling
Before anything is touched, we photograph the stack from every face and note its height, the number of pots, the shape of any corbelling (courses that step outwards near the top) and the bond pattern, which is the way the bricks or stones are arranged in each course. Those records are how the stack goes back looking as it did. On a house where the stack is part of the street, we would rather spend an hour recording than have a rebuilt stack that reads as a different shape from the neighbours.
Making the roof safe
The roof around the stack is protected before dismantling begins. Falling masonry cracks slates and tiles, so the slope is covered first. Pots are lifted off and set aside, and flues are covered while work goes on.
Dismantling course by course
The stack is taken down from the top, one course at a time, with the units sorted as they come off. Sound bricks or stones are cleaned of old mortar and stacked for reuse. Units that have split, flaked or lost their faces are rejected. A stack with a lot of rejects needs more new material than owners expect, which is one reason a firm figure has to wait for the survey.
Checking what is beneath
With the shaft down to sound masonry we look at what it stands on: the bed at roof level, any flue liner, and signs of damp or movement below. If the fault started lower down, rebuilding the top would only repeat it.
Building back up
New courses go on in the recorded bond, using a mortar matched to the age of the stack. The flues are kept clear and straight. The flaunching (mortar sloped up round each pot to shed water) is formed at the top, and the pots are bedded back, or new ones fitted where the old ones have cracked. New lead goes in last, sealing the base of the stack against the slope.
Matching brick, stone and mortar
A rebuilt stack that does not match the house shows from the lane. The match has three parts: the units, the bond and the mortar.
Bricks
Reusing the original bricks is the first choice, because colour, size and weathering already match. Where new bricks must be added, we hold a sample against the stack before ordering. Older bricks often differ slightly in size from modern ones, which changes joint thickness and how the courses line up.
Stone
On stone houses the principle is the same, with an extra care. Cotswold stone is limestone, and our guide to stone chimneys in Stroud explains why it needs a different mortar and a different eye from brick. New stone must be the same geology, colour and grain as the old, so limestone never replaces sandstone. Cotswold District Council's 2000 guidance reproduces English Heritage policy to that effect for roof slates, and the same logic carries over to a stack.
Mortar
The mortar must not be harder than the masonry it holds. A hard cement mix in a soft brick or stone stack pushes moisture out through the masonry instead of the joints, and the units start to flake. That is the reverse of what a joint is for. For older stacks we normally use a lime-based mix; for a modern stack in hard bricks, a stronger mix may be right. The choice is made on the stack, not on habit.
If a quote for a rebuild does not say what mortar will be used, ask. The answer tells you a good deal about how the stack will weather.
Our guide to the best mortar for chimney repairs compares the mixes in more detail.
Scaffold, access and the way up Stroud's steep streets
A rebuild needs a proper working platform. Dismantling a stack and laying fresh courses involves weight, tools and several people at height, so the platform must be wide, stable and edge-protected. A roof ladder and a harness are enough for a quick look; they are not enough for a rebuild.
What the scaffold has to do
The scaffold carries the workers, gives a place to stack bricks and sand, and shields the roof and the street from falling debris. It also has to reach the stack. A stack well back from the eaves can need a platform across the slope as well as the lift up the gable.
Access in the valleys
In and around Stroud, stacks are often reached through terraced streets, shared lanes and sloping plots. Deliveries of sand, lime and bricks cannot always come to the door, and the scaffold may need to stand on a pavement, a steep verge or a neighbour's land. The survey takes all of that in, and the written quote prices it. If the scaffold crosses a boundary, we raise it with you early, because it needs the neighbour's agreement before work starts.
Scaffold cost
Scaffold is a real cost in the price. MyBuilder's 2026 guide gives about £1,125 for a re-roof scaffold, and Checkatrade's October 2026 guide £700 to £1,300. One stack needs less than a whole-house scaffold, but on a small job it can still rival the masonry cost.
Our separate guide to scaffolding for chimney work goes into the options in more depth.
Lead, soakers and the roof around the rebuilt stack
The seal between a stack and its roof decides whether it stays dry. When the masonry comes down, the lead that seals that joint comes with it, or is exposed and often reused only with difficulty. A rebuild is the best moment to renew it.
The parts of the flashing
A chimney is flashed in sections. The apron sits on the downhill face, the step flashings run up the sides, and the back gutter, a small valley behind the stack, carries water round it from the uphill side. On slate or tile roofs, soakers (small bent lead sheets interleaved with the slates or tiles) work with the step flashings to keep the side joints dry. Each piece is tucked into a raked-out joint in the masonry, or into a lead chase cut for the purpose, and wedged and pointed.
Lead code
Sheet lead comes in codes from 3 to 8, each a set thickness. Leadworx names Code 4 (1.80 mm) as its standard for general flashing, and thinner Code 3 (1.32 mm) for soakers. The code is named on our quote, so you know what goes on. MyJobQuote (updated September 2026) puts well-fitted lead flashing beyond 80 years, and higher codes beyond 100. Treat that as a typical range, never a promise.
Lead costs on a rebuild
In Checkatrade's 2026 repair guide, lead repairs run £50 to £70 per metre and stepped flashing £80 to £120 per metre, Code 5, excluding VAT. Because a rebuild exposes every joint, the flashing is usually priced as part of the stack, not as an extra. If a quote does not say what lead is being used, ask.
Slipped or cracked slates and tiles beside the stack are put right while the scaffold is up, so you do not pay for access twice.
Consent, listed buildings and party stacks
Rebuilding a stack in the same place, the same size and the same material is, for most houses, like-for-like repair. The 1990 planning Act (Town and Country Planning Act, section 55) says work that does not materially affect how a building looks outside is not development. A faithful rebuild is therefore rarely a planning matter. The words "faithful" and "usually" matter: a taller stack, a different brick or a changed shape could alter the appearance, and then the answer changes.
Listed buildings and conservation areas
If your house is listed, the position is stricter. Stroud District Council says the whole building, inside and out, is protected whatever the grade. Changing a listed building's character without listed building consent is an offence, and that can include a changed stack. Stroud District has 41 conservation areas, and five carry Article 4 Directions, including Bisley and both Stroud town areas. The council has not said whether these reach roofs and chimneys, so put the question to its planning team before booking. Our guide to listed chimney repairs covers this in detail.
Building Regulations
Whether a particular rebuild is notifiable is a question for building control, and we do not guess at it. Stroud District's building control is the Gloucestershire Building Control Partnership, and a registered building control approver is the private route. If it is notifiable, we handle the notification as part of the job.
Shared stacks
Terraced and semi-detached houses often share a stack with next door, so a rebuild affects both owners. Talk to your neighbour before the survey, so access, scaffold and any sharing of cost are settled in advance.
What a rebuild costs and what the quote should show
The only sourced national figure for a stack rebuild is MyBuilder's: between £2,000 and £10,000 or more, in its guide updated in August 2026. That width is wide because the jobs differ. A short brick stack on a bungalow, with two courses to replace, is nowhere near a tall stone stack on a three-storey house taken down to the roofline.
Height, flue count, material, the volume of new brick or stone, scaffold and lead renewal all move the price. So does access on a steep valley street, which we put in the quote rather than discover on the day. In the same MyBuilder guide repointing averages about £750, which shows the gap: a rebuild is a different job, not a repair at a higher rate.
Reading the quote
After the survey, our written quote covers scaffold, dismantling, new materials, rebuilding labour, lead, pots and flaunching, waste, and making good. It is one price for the whole job. VAT appears on your quote, because roofing work is normally standard-rated.
You will also have photographs of your own stack from the survey, which show what was found and why the rebuild was recommended. The site is cleared and waste taken away at the end, and the work carries our written 10-year workmanship guarantee.
As a first step, send photographs of the stack from the ground or an upstairs window, with a note of which side of the house it is on.