Start with what remains
Ask the engineer to establish which parts of the breast and stack are being removed, which remain and how they are supported. Include previous alterations on both sides of a shared wall where that information can be obtained. Do not assume that the chimney is supported merely because it has stood since an earlier removal.
Redbridge's guidance requires suitable support for retained masonry and treats the support design as part of the building-control information. A hidden support should be investigated rather than inferred from a finished ceiling. [2]
Why borough advice matters
Harrow's October 2024 guidance restricts the use of gallows brackets and specifically addresses cases where the neighbour's breast has already been removed and supported on brackets. Its requirements are local guidance for the described circumstances, not evidence of a London-wide prohibition. [1]
Redbridge currently requires structural calculations and pull-out testing for gallows-bracket proposals. That published requirement means a sketch showing brackets is not, by itself, the complete evidence needed there. Confirm the relevant building-control body's requirements for your address. [2]
What a beam solution needs
A steel beam transfers load to its end supports. Those supports, their masonry and any necessary load-spreading details must be adequate; selecting a beam alone does not complete the design. The beam may also need fire protection appropriate to its structural role. [3]
Ask the engineer to show the proposed support in section as well as plan, especially where it affects headroom or the loft floor. Request a coordinated detail that the builder can set out without deciding the structural arrangement during demolition.
The neighbour's rights are separate
GOV.UK identifies removing a chimney breast from a party wall and cutting into a party wall for a beam among the works that require notice under the Party Wall Act. Structural adequacy does not remove that requirement, and a party wall agreement is not a substitute for building-regulations approval. [4]
For an unusual shared stack, ownership dispute or disagreement over access, obtain project-specific party wall advice before deciding how the work will proceed.
Plan removal and inspection
The masonry must remain stable during removal. HSE's demolition guidance requires the method to account for the structure's condition, load paths and how stability is maintained as work proceeds. [5]
Do not treat removing the breast first and supporting the stack later as a design strategy.
Before starting, request the support calculations, installation detail, inspection arrangements and confirmation of who will answer site queries. At handover, retain the final design, any test results and the building-control documentation. Record departures from the original proposal rather than leaving future owners to guess what lies behind the plaster.