Removing a Chimney Breast and Supporting What Is Left

Draw the Whole Stack Before You Draw the Cut

Almost every mistake here is made by treating the breast as a wall panel and forgetting the parts you cannot see from the room. Go into the loft with a tape first: the roof-space stack is usually narrower than the breast downstairs because the flues have gathered, so measure its plan size and its height to the roof line. Then measure outside, from the highest point where the stack passes through the roof surface to the underside of the flaunching, and count the pots. That upper section is what everybody underestimates — from the ground it looks like a chimney, and on a load sheet it is half a tonne of brickwork with a lever arm.

It also carries its own rule. Approved Document J to the Building Regulations sets the stability limit for a masonry chimney standing clear of the roof: height above the highest point of intersection with the roof surface should not exceed four and a half times its least horizontal dimension, unless it is designed for wind loading or restrained. That rule assumes the stack is continuously supported from below. Removing part of that support does not change it, but a stack that was already borderline is now sitting on a detail rather than on masonry.

Turning geometry into weight is arithmetic provided you are honest about the density. Solid clay brickwork is commonly taken at 18 to 22 kN per cubic metre — the range in the density tables of BS EN 1991-1-1, Eurocode 1, Actions on Structures — roughly 1,800 to 2,240 kg/m3, or 112 to 140 lb/ft3. Take the high end for dense units in cement mortar, the low end for soft handmade brick in lime. Then subtract nothing for the flues: the void is real on a four-flue stack, but parging, soot, nest debris and the solid corbelling at each gather put most of it back.

Keep the three pieces apart, because three different checks want them. Above the roof, flaunching and pots included, governs stability in wind. The roof-space section plus the first-floor breast is what the props hold. All three together are what the permanent support carries for the life of the building, and that is the number on the drawing.

Holding a Column, Not a Line

Propping is temporary works under BS 5975, and the sequence for holding a wall while the member under it is changed is set out in the failed lintel guide rather than repeated here. What is different about a breast is that you are not supporting a line of wall. You are supporting a block: a concentrated mass, deep front to back, tall, and free to fall in a direction a wall panel cannot.

The first consequence is that needling often does not work. A needle relies on passing a member through the full thickness of solid masonry and propping both sides, and the middle of a breast at the height you would want to needle is flue void. Drilling through and finding air is the good outcome; the bad one is a needle bearing on a withe. The usual answer is props to a spreader under the retained breast, with masonry support heads clamped into raked bed joints in the flank and party walls either side — and the published safe working load of the attachment governs, not the prop's, as Acrow's Strongboy literature makes clear.

The second consequence is the one that hurts people. The moment the base is out, what stands above it is a slender pier of masonry two storeys and a roof high, restrained only by whatever is genuinely tied to it at floor and roof level. It has no reserve against a sideways push, and a strut kicked out at the bottom is exactly a sideways push. Restrain it laterally before taking any load off it.

The third is mundane and expensive. On a ground floor you are frequently standing props on two different worlds a metre apart: one foot on the hearth slab or the old fireplace base, which is solid, the other on suspended timber with a joist that may be trimmed and doubled around the hearth, or may not be. Establish what each foot stands on individually; the sole plate arithmetic itself is common to all propping and the lintel guide covers it.

1. Get the party wall notices served and their periods run before anything is booked in.
2. Measure the roof-space stack and the above-roof stack separately, and count the pots.
3. Lift a board or open a perpend to find what each prop position is standing on.
4. Restrain the retained breast laterally before any load comes off it.
5. Load the props by hand to snug, against a spreader catching the full depth of the breast rather than its face.
6. Leave the props standing until the permanent support is bedded, packed solid to the masonry above, and the packing has gained strength.

Turning a Block of Masonry Into Something a Beam Table Recognises

Where brackets are refused, or the stack is too heavy or the wall too poor for them, the answer is a beam spanning the width the breast occupied, landing on the flank wall at one end and the party wall or a pier at the other. That beam carries a concentrated load — the retained breast bearing across roughly its own footprint — rather than the uniform load every published lintel safe working load table is written around. Using a table figure here is the specific error the failed lintel guide warns about, and this is the case you are now in.

There is a legitimate screening step, and it is worth knowing exactly what it covers. Convert the concentrated load to the uniform load producing the same peak bending moment: for a load W at mid-span of a span L, w equals two W over L, because a central point load gives a moment of WL over four and a uniform load gives wL squared over eight. Off centre, with the load at distances a and b from the supports, the equivalent is eight W a b over L cubed. The substitution is exact on bending and high on deflection wherever the load sits, about a quarter high at mid-span. End shear is the exception: twice the true figure at mid-span, but lower than the point load's own once the load sits nearer a support than a quarter of the span. That is what makes it usable as a screening figure and useless as a design: it tells you honestly whether a candidate section is nowhere near or in the region, and never that it is adequate.

Two things end the screening and start a real design. A breast rarely lands neatly at mid-span, so the true case is a patch load with unequal reactions, and the smaller reaction is not the one that governs the bearing. And the beam is holding up masonry with plaster on it, which means deflection under permanent load decides the section rather than strength — the argument the steel beam guide makes at length, and the reason a section that passes on bending can still crack the ceiling it was installed to save.

Two Ends, One of Which May Not Be Yours

The reaction from either scheme has to cross into masonry, and the masonry here is poor at both ends. On the flank side the beam frequently lands on the short return between the breast and the external wall, which in a great many houses is a half-brick pier a few hundred millimetres wide that was never intended as a bearing. On the party side it lands in a wall shared with next door.

Bearing length is the item people shave to make a member fit an existing gap, and shaving it does not derate the member gracefully — it takes it outside the case its capacity was published for. The minimums by member type, and where each comes from, are tabulated in the failed lintel guide. What is specific here is the stress rather than the length: a padstone spreading the reaction over enough area that the masonry beneath stays inside its allowable bearing stress, a separate check governed by TMS 402/602 and by BS EN 1996-1-1. A long bearing on a soft pier still crushes.

Cutting the pocket in a party wall is the moment you find out how thick that wall really is. A one-brick wall with a 100 mm padstone in it has lost half its thickness over the length of the pocket, and what sits behind the padstone is the neighbour's plaster. The usual answer is a shallower pocket on a longer padstone, or a post carrying the beam end down beside the wall rather than into it. Whichever it is, the dimensions belong in the notice before the surveyors see them, not after.

Taking It Down in Courses

With the props standing, the breast comes down from the cut line, course by course, never by knocking the bottom out and letting the rest follow. Victorian and interwar brickwork in lime mortar comes apart along the joints with a bolster far more readily than a breaker will convince anybody, at a fraction of the dust and none of the vibration. Cement-mortared work from the 1960s onward does not, which is where the breaker earns its place — though a breaker held horizontally into a wall you are standing beside is also how props get knocked.

The arisings are not one material. Face brick in lime mortar releases cleanly and is worth stacking rather than tipping, both because reclaimed brick has value and because sorted brick is lighter to dispose of than mixed rubble. Behind it there is parging and soot off the flue face, usually a barrow of nest debris and loose fill from the gathering, and at the bottom the constructional hearth — the slab of solid non-combustible material Approved Document J requires under a solid fuel appliance, in the order of 125 mm thick and wider in plan than the breast above it. That slab is concrete rather than brick and it is the heaviest lift of the day per barrow.

Then the volume, which always surprises. The example breast is 1.35 m wide by 0.34 m deep by 2.5 m high, a little over a cubic metre in place, and it looks manageable while it is still a wall. Broken up it is not: masonry swells because breaking it introduces voids, and the swell factors published in the demolition estimating literature are how you get from the solid figure the tape gave you to the loose figure everything downstream is bought against. That conversion's general logic belongs to the demolition planning guide; what matters here is running it before booking a container, because the in-place figure fits in a box the loose figure will not.

The Wall Behind the Breast Is Thinner Than You Think

The first thing the empty corner shows you is how much wall there actually was. In a great many terraced and semi-detached houses the party wall behind the fireplace recess is a half-brick skin, because the breast made up the thickness and nobody built a full brick behind a projection already 340 mm deep. Removing it therefore does not leave a flat party wall; it leaves a full-height panel of 100 mm masonry between two dwellings that now has to satisfy fire separation under Approved Document B and sound insulation under Approved Document E on its own. It usually cannot. Blockwork built against it, an independent lining, or a designed separating construction is the fix, and it is the line item missed in almost every quote written from the doorway.

The second is the flue apertures. Where the throat gathered there will be openings in the wall face, and where a withe has gone there may be a route straight into the neighbour's flue. Those get built up solid in dense units bonded into the surrounding brickwork, not foamed and skimmed. Any flue above that is now permanently out of use is capped and, following Approved Document J's guidance on disused flues, ventilated top and bottom — a sealed damp flue in a party wall drives salts through the plaster on both sides, and the neighbour sees it first.

Take the quantity off what you are building rather than off the room: the make-good panel, the flue apertures, the toothing into the flank wall where the breast was bonded in, and any rebuilt pocket at the bearings. Set the unit size and joint width to the wall you are tying into rather than a nominal, because the courses have to line through with what is already there.

The Weighbridge Ticket Audits the Number You Started With

Here is a check nobody does and everybody should. The masonry you take out and the masonry you leave above the cut were built as one continuous stack, from the same brick and the same mortar, in proportions you have already measured. So the tonnage that leaves the site is an independent measurement of the density you assumed when you weighed the remainder — and the remainder is the number the whole support decision rests on.

Convert the loose volume into tons, then work backwards: divide the weighbridge tonnage by the solid in-place volume the tape gave you and you have this building's real brickwork density rather than a table value. If it lands inside the Eurocode 1 range you assumed, the load on the brackets or the beam is what you told building control it was. If it comes out well above, the stack is heavier than the calculation said, and the time to say so is while the props are still standing rather than after the plasterer has been. It costs one phone call for the ticket, and it is the only chance the job offers to test an assumption against a measurement.

Where the Box Stands, and What Must Not Go In It

Chimney rubble fails on weight rather than volume, the opposite of most refurbishment work. A cubic metre of solid brickwork is around two tonnes in place — 1.8 at the soft end of the density range, 2.2 at the dense end — and still heavy once broken, so a container ordered for the loose volume reaches its permitted weight while it looks part full. Check the two constraints separately and take whichever binds first.

Access decides the rest. In a terrace with no driveway the container stands on the highway, which under the Highways Act 1980's builders' skip provisions needs a permit from the highway authority together with lighting and markings. Where that is not available the fallback is bulk bags, and a bag rated at a tonne fills with brick rubble long before it looks full — one the crane will not lift is an expensive ornament in a front garden. Either way there is a barrow route through a furnished house and, on an upstairs breast, a flight of stairs; the Manual Handling Operations Regulations 1992 are why that route is planned rather than discovered on the day.

One stream does not go in with the rest. Material scraped off the flue face — soot, tar and creosote from a flue that burned coal or wood — is not clean brick rubble, and whether it classifies as hazardous is answered by the waste classification guidance the UK environment agencies publish as WM3, not by the skip company's price list. Bag it separately and describe it accurately on the transfer note: the duty of care under the Environmental Protection Act 1990 sits with the producer however the load was filled. And if the breast face carries a textured coating of any age, that is settled before a tool touches it under the Control of Asbestos Regulations 2012 — the testing sequence is covered in the lath and plaster ceiling guide.