Chimney breast removal: what is involved and how to do it safely

Do I need a structural engineer to remove a chimney breast?

Yes, in almost every case. Removing a chimney breast is a structural alteration, so it needs Building Regulations approval and calculations showing how anything left above will be supported. If you take out the breast downstairs but keep the one above, or keep the stack on the roof, that masonry must be carried on a properly designed steel beam or approved brackets. Most chimney breasts in London terraces are also built into the party wall, so party wall notices are usually needed too.

A chimney breast is heavy. A two-storey breast with its stack can weigh several tonnes, all bearing down through the brickwork you are planning to remove. Unsupported breasts are a defect engineers find regularly in London houses, often years after the work was done.

Building Control approval can be sought through a full plans application or, for many domestic jobs, a building notice. Either way, the inspector will want to see the engineer's calculations for the steelwork and inspect it before it is covered up.

Your options for removal

There are three broad approaches. The right one depends on how you want to use the space, the roof and what your neighbour has already done.

• Remove the ground floor breast only, supporting the upper breast and stack on a beam or brackets
• Remove the breast on every floor, supporting the stack in the loft on a beam
• Remove everything, including the stack above the roof, so nothing is left to support

Choosing between partial and full removal

Full removal is the simplest structurally, but taking down a stack changes the roofline and may need planning permission, particularly in a conservation area or on a listed building. Shared stacks also contain flues from the house next door, so you usually cannot remove the whole stack without involving your neighbour.

Partial removal is common because it leaves the outside untouched. It does mean adding steelwork, and the design has to make sure the beam bears onto walls that can take the extra load. Older walls with soft mortar or past alterations sometimes need padstones or local strengthening.

Think about the services too. Old breasts often hide gas pipes, cables and the remains of flue liners, and a working gas or solid fuel appliance upstairs may still rely on a flue running through the part you want to remove. These need checking before any design is finalised.

Steel beams and gallows brackets

The traditional shortcut was a pair of steel gallows brackets fixed to the wall beneath the remaining breast. Many Building Control bodies now accept brackets only in limited circumstances, such as where the remaining breast is modest, the wall is in good condition and the brackets follow a proven detail. Where those conditions are not met, a steel beam is needed.

A beam normally spans across the line of the breast and bears onto the front or rear wall, or onto the party wall with padstones to spread the load. Sometimes two beams are used with a plate between them under the breast. In the loft, a beam between the party wall and a spine or flank wall can carry the stack once the lower breasts have gone.

Steelwork supporting masonry over a habitable room needs fire protection, usually plasterboard. Our chimney breast or stack alteration design, from £350 + VAT, covers the assessment, the support design and the calculations Building Control will ask to see.

Party walls and your neighbour's chimney

In most London terraces and semis, chimney breasts sit back to back with the house next door, sharing the party wall and often the stack. Removing your breast means cutting into the party wall, which needs a party structure notice under the Party Wall etc. Act 1996, with two months' notice. Our guide to the Party Wall Act and structural works explains how notices work.

Your neighbour's breast matters too. If they have already removed theirs, the masonry left in the wall may be thinner and more heavily loaded than it looks, and the stack may be relying on your breast for support. The design has to account for both sides of the wall, and a schedule of condition of the neighbour's rooms before work starts protects everyone.

Building the removal safely

The sequence matters as much as the design. Before any brickwork comes out, the masonry above is supported on temporary props and needles. The breast is then cut out carefully, the permanent beam or brackets installed and packed tight to the masonry above, and only then are the temporary supports removed. Details that are easily missed include:

• Capping the stack and ventilating disused flues to prevent damp
• Checking that no flue in the remaining breast still serves a working appliance
• Making good the floor and ceiling where the hearth and breast were
• Fire protection to the new steelwork
• A Building Control inspection before the steel is boxed in

Bought a house where the chimney breast has already gone?

This is very common in older London housing, from Islington to Wandsworth. Breasts were often removed decades ago with little or no support, sometimes leaving the breast above held up by the bond of the brickwork alone. Warning signs include cracks in the ceiling or wall where the breast used to be, a sagging breast upstairs, cracked brickwork in the loft and a leaning stack.

Ask the seller for the Building Control completion certificate and any engineer's calculations. If there are none, a chimney stability report checks what is actually supporting the remaining masonry and whether it is safe. Like all our inspection reports, it is signed off by a chartered engineer who is a Member of the Institution of Civil Engineers (MICE). Where support is missing or inadequate, we design the remedial steelwork so the work can be regularised with Building Control.