Chimney Breasts and Stacks in a Loft Conversion
Above the ceiling joists a chimney stops being a lump in a wall and becomes a tonne of brickwork standing in the wind.
Downstairs, a chimney breast is a lump in the middle of a wall that spoils a furniture layout. Up in the roof it is a different animal: it stands where the head height is best, it lands where the dormer wants to go, and on a semi or a terrace it is usually built into the wall you share with next door. This page is about the part of the chimney above the ceiling joists. The ground floor question, where the breast comes out as part of an opening, is covered on the open plan living page.
What is actually up there
A chimney is not one thing. It is four, stacked, and each of them behaves differently.
At the bottom sits the ground floor breast with the fireplace opening in it. Above that, a first floor breast, usually narrower, often with a second opening bricked up behind the plaster. Above the ceiling joists the breast continues through the loft, still carrying the flues, and above the tiles it becomes the stack: brickwork standing free in the weather, with flaunching and pots on top.
Inside, the flues are separated by a thin brick division called the withe or the midfeather, rarely more than half a brick thick and usually built in lime mortar that a century of sulphates has not improved. That thin division matters more than the outside of the stack does, because it is what keeps one flue’s smoke out of another, and on a terrace it is frequently the only thing between your flue and a neighbour’s.
The weight is worth stating. A modest stack standing a metre and a half above the tiles, plus its pots, is comfortably a tonne of brickwork, and it is a tonne sitting on a cantilever in the wind rather than resting quietly on the ground. That combination is why the structural conversation about a chimney is different in the loft from anywhere else in the house.
Three things you can do, and the situation picks for you
Almost every loft conversion ends up at one of three positions, and the fires downstairs usually decide which.
| Option | When it is the answer | What it costs you |
|---|---|---|
| Leave the whole chimney alone | A live fire below, a stack shared with a neighbour who has one, or a listed building. | Floor area at the best headroom, and a dormer or a stair that has to be planned around it. |
| Remove everything above the ceiling joists, stack included | The flue is redundant and nobody next door depends on the stack. | Roof opening to trim and weather, scaffolding, and the fireplaces below become decorative for good. |
| Remove the loft breast but keep the stack above the roof | The stack is a shared or matched pair, or the council wants it kept. | The hardest of the three. A tonne of brickwork now has nothing under it, and that has to be designed. |
Most people arrive assuming they want the second row and discover they are in the first or third. Which row you are in is worth establishing before the loft is designed, because it changes the plan rather than the finish.
Taking it out from the ceiling up
The clean version of this job removes the whole chimney above the ceiling and leaves nothing needing support.
This is the one worth aiming for. Everything above the ceiling joists comes out, the stack included, so the breasts on the two floors below are left carrying less than they were built to carry, which is a direction structures do not mind. There is no residual load and no ongoing risk, and no bracket anywhere.
The stack comes down course by course from a scaffold, from the top, into a chute. It is not pushed over, whatever a video suggests, because a tonne of brickwork landing on a roof slope goes through it. The masonry through the loft comes out next, the flue below is capped, and the opening in the roof gets new timbers trimmed round it before the covering is made good.
Two details get skipped and both cause damp. The capped flue below needs ventilating at the top and at the bottom, so air moves gently through it and the salts in the old brickwork stay dry. And the breast that remains downstairs needs the same treatment: a sealed disused flue is precisely how staining appears on a bedroom chimney breast two winters later.
This is building work under the Building Regulations, whatever the planning position. It is a structural alteration, it is notifiable, and it goes to a building control body either as a building notice or on full plans. On anything with an opening or a beam in it, full plans is the route worth taking.
Gallows brackets, and why the loft is where they get refused
A gallows bracket is a pair of steel angles bolted back to the wall either side, carrying the brickwork you have left above.
They exist, they are used, and they are accepted in limited circumstances only. The wall they bolt into has to be sound solid brickwork of adequate thickness, the load above has to be modest, and the retained masonry has to be in decent order. Colchester City Council Building Control, like most authorities, looks at them closely, and frequently asks instead for a beam bearing onto padstones each side, which is more robust and not much dearer.
Up in the roof the case is weaker than it is downstairs, for reasons worth spelling out. The load being retained is the entire stack, exposed to wind, which puts an overturning force into the bracket rather than a simple downward one. The brickwork you are bolting into is at the top of the house, where the mortar is oldest and the weather has been at it longest. There is often no return wall to help. And on a semi or a terrace the wall in question is the party wall, which means bolting into masonry that is not wholly yours.
So the honest position is that gallows brackets are the answer to a narrow question and not a general technique. Where a stack genuinely has to be retained above a removed breast, the calculation belongs to a structural engineer, and the design that comes back is as likely to be a beam on padstones, or a steel frame carried down to a wall that can take it, as a pair of brackets. The same logic that governs removing a load bearing wall applies here, with wind added.
A fire still in use downstairs changes the answer
You cannot remove the flue and keep the appliance. There is no version of that job.
A working fire needs its flue to run from the appliance to open air at a position the Regulations accept, and Approved Document J is specific about where that position is. For a solid fuel appliance, a flue outlet at or within 600mm of the ridge must terminate at least 600mm above the ridge. Anywhere else on the roof it must be at least 2300mm horizontally from the nearest point of the roof surface, and either at least 1000mm above the point where the chimney passes through it, or as high as the ridge.
Read that against a loft conversion and the conflict appears immediately. People want the stack cut down so it disappears behind a new dormer, and a truncated stack usually fails the outlet position for the appliance still burning below it. Lowering a stack is not a cosmetic decision; it is a change to a working flue.
The routes out are limited and worth knowing early. Decommission the fire, cap and vent the flue and take the whole chimney out. Keep the masonry breast running up through the new room, reline the flue and design the room around it, which loses the space but keeps the fire. Or replace the masonry flue with an insulated twin wall system routed through the new structure to a compliant terminal, which is a real piece of work with its own clearances to combustible material and its own inspection. A carbon monoxide alarm goes in wherever a fixed combustion appliance is served.
One more thing about relining. A flue that has been kept in service is not the same as one that has been shut for thirty years and is now being brought back because a wood burner is in the plan. That one gets swept, inspected and usually lined, and the loft conversion is the moment when the whole length of it is accessible for the only time in its life.
The shared stack, and the two months you did not budget
On a semi or a terrace the stack is usually a party structure, and half of it is not yours to remove.
Where a stack sits on the party wall, the flues inside it belong to both houses and frequently cross over on their way up, so your neighbour’s smoke may be travelling through brickwork on your side. Taking your half away exposes their flues, removes the restraint from the remainder, and leaves a raw face standing in the weather. Surveyors regularly conclude that a shared stack comes down entirely or stays entirely, with the middle option being the worst of both.
Legally this is section 2 of the Party Wall etc. Act 1996: work to an existing party structure, which expressly includes removing a chimney breast. The notice period is at least two months, and it is shortened only by the adjoining owner consenting in writing, not by everybody being reasonable about it. The mechanics, and the notice document itself, are set out in the Party Wall Act explained.
What the Act does not do is give you a right to take away something your neighbour depends on. If their flue is live and it runs in the stack you want down, the answer is that the stack stays, and no award will produce a different one. That is not an obstacle a builder can work around, and it needs establishing before a plan is drawn rather than after.
The advice that costs nothing still applies. Knock on the door with the drawings before the notice lands on the mat, and get a schedule of condition done. On terraces around the older parts of Colchester, where the stacks are often shared three or four ways along a row, that conversation is the difference between a straightforward job and an eighteen month argument about a crack.
The roof, made good
The hole left by a stack is in the worst place on the roof, and it is where a badly done job leaks.
Where the chimney passed through, rafters were cut and trimmed around it when the house was built. Taking the chimney out means putting that structure back: new trimmers, new rafters, the underlay lapped correctly into the existing rather than butted, then battens and covering. Where the stack came through at or near the ridge, the ridge itself has to be remade.
The covering is the part that surprises people. Tiles taken off a hundred year old roof are not tiles you can buy, and a patch of new ones in the middle of a weathered slope announces itself from the garden. The usual answer is to salvage from the slope that is about to be dormered anyway and put the new material where it will be hidden. That only works if the sequence is planned, which is another reason the chimney decision belongs at design stage.
Where half a shared stack stays, the junction between the retained brickwork and the made good roof needs proper flashing: soakers up the slope, a back gutter on the uphill side, an apron below. It is not a job for a tube of sealant, and it is the single most common place a leak appears on a house six months after a conversion.
Planning, briefly, and the paperwork afterwards
Taking a chimney out is mostly a Building Regulations matter, with two exceptions that are worth checking rather than assuming.
Removing a breast internally is not something a planning application is normally made for. Taking the stack off the roof changes the outside of the house, and there the position depends on where the house is. Inside a conservation area the loss of a stack from a roofline is exactly the sort of change an officer has a view about, and that view is far cheaper to obtain before the scaffold goes up: our page on extending in a conservation area covers how designation changes who decides. On a listed building it is listed building consent territory, under separate legislation where unauthorised work is a criminal offence, and the listed building answer sets out how the two consents run alongside each other.
Whichever route applies, keep the completion certificate for the structural work with the deeds. A first floor or loft chimney breast with nothing beneath it, and no paperwork behind it, is one of the things a surveyor flags at the next sale. Its absence does not mean the support is inadequate. It means nobody has checked, and the buyer’s side will price that uncertainty rather than ignore it.
We settle the chimney question at survey, before the loft is designed, because it moves the stair, the dormer and sometimes the whole plan. If you have a stack in the way of the conversion you want, that is the point at which the options are still open.
The outlet positions and notice periods described here are current at the time of writing and depend on your appliance, your roof and your neighbour’s arrangements. Treat this as an explanation of how the decision works rather than as confirmation of what your chimney will allow.
Last reviewed August 2026. Planning and Building Regulations change, and your property may differ.
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