The short answer
If a chimney breast was removed below and the stack still stands above the roof, something must now carry that weight. Warning signs are sagging or cracked ceilings and walls near the old breast, cracks in the stack, or a stack that leans. A structural engineer's calculation, plus a look at the supports in the loft, settles whether the stack is safe or needs attention.
What carries a stack once the breast below has gone
A chimney breast is the mass of brick or stone that projects into a room and carries the flues up through the house. The stack, the part you see above the roof, sits on top of that mass. Take the breast out of a ground-floor room, or out of both storeys, and the weight of the stack has to travel somewhere new. When the work was done properly, a steel beam or a pair of beams, often with posts or gallows brackets (steel supports fixed to the wall), takes the load and passes it into the walls either side. Done badly, or not at all, the brickwork above simply hangs there, held up by little more than the bond of old mortar.
A house can have had a breast removed before you bought it, and the stack is often left because it looks harmless from the road. Our page on whether you need a sweep or a roofer explains who looks at which part of a chimney. The question here is narrower: was the support put in, and is it still doing its job? Our wider chimney repairs pages cover the rest of the stack.
Signs inside the house
Look first at the rooms around where the breast used to be. A ceiling that has dipped, a diagonal crack running from the corner of the old breast, or plaster that has split where the missing breast met the wall are all worth noting. Cracks that reopen after filling matter more than a single hairline that has stayed the same. Doors and windows near the old position that start to stick can point to movement in the wall above.
In the bedroom or landing above, check the ceiling and the floor level. A bulge in a floor, or a slope you can feel underfoot, suggests that load is bearing somewhere it was never meant to. Take dated photographs of any crack with a coin or ruler beside it. They make it far easier for an engineer, or for us at survey, to judge whether the movement is old and settled or still going.
None of these signs proves the stack is unsafe. Plenty of cracks come from ordinary settlement or drying out. They simply tell you where to look next.
Signs on the roof and in the loft
From the garden or pavement, look at the stack itself. A stack leaning out of true, horizontal cracks across the brickwork, bricks that have shifted, or a gap opening where the brickwork meets the slates all deserve attention. Pots that tilt, or flaunching (the mortar cap that beds the pots) that has cracked and dropped away, can be a symptom of movement lower down rather than weathering alone. Our guide to a leaning chimney covers the outward lean in more detail.
The loft tells the most. With a torch, look at where the stack comes through. You are looking for the support: a steel beam, brackets fixed to the walls, or properly built brickwork carried on a lintel. Missing support, timber props, a stack sitting on loose bricks, or old rafters and purlins cut away around the stack are all red flags. Never lean on or move anything up there, and never step off the joists. If the loft has no boarding, stay at the hatch and use a phone camera on a long reach instead.
The structural checks that settle it
Taking out a breast is a Building Regulations matter every time, according to the Planning Portal, and its advice is to bring in a structural engineer. So a legitimate removal leaves a paper trail: calculations for the support, a sign-off from building control, and in a semi or terrace possibly a party wall notice. Ask the seller's solicitor, the previous owner or the council's building control team whether those papers exist. Our page on permission to remove a chimney lists what should have happened.
Where there are no papers, a structural engineer can inspect the support, calculate what the stack weighs and say whether the beam, brackets and bearings are adequate. Regularisation is available for work already done, which the council's building control pages describe. If the stack is found wanting, the usual answers are to add proper support, to rebuild the stack lower, or to take it down to roof level and make the roof good. Which one suits depends on the survey, the stack's condition, and whether neighbours share it. See our page on shared chimney stacks if you have a party wall.
Where a roofer fits in
On the roof we examine the stack, the pots, the flashing, the flaunching and the loft side, and take pictures as we go. A written quote reaches you once the visit is done. We cannot sign off the structure of a beam or bracket, and we do not pretend to; that is the engineer's job. What we can do is flag a stack that looks unsupported and tell you plainly that it needs an engineer before any repair money is spent on it.
If the stack is sound, a repair to the brickwork, pointing or flashing is a normal job, and our page on how long chimney repairs take sets out what to expect. If the stack is listed or in a conservation area, check with Swindon Borough Council's planning team before changing it; our page on listed chimney repairs explains why. Where a stack proves beyond saving, the right job may be the modest one. Sometimes that means taking the stack down to roof level rather than propping it for another round of repairs.
Questions to put to a seller or a previous owner
If you are buying, or have just bought, a house with a missing breast, a short list of questions saves worry later. When was the breast taken out, and who did it? Is there an engineer's calculation or a building control certificate? Was a party wall notice served on the neighbour? Was the stack left, shortened or rebuilt afterwards? A clear paper answer to each is reassuring, and a vague one tells you an inspection is worth paying for.