D1 Chimney stacks
2There are two brick chimney stacks, one on each party wall, each shared with the adjoining houses. The stacks carry several clay pots, some of which are uncapped, and the tops are weathered with a mortar flaunching.
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The brickwork shows weathering and open mortar joints at high level, and the flaunching is cracked. Chimney stacks, fillets and flashings are very exposed and should be regularly inspected and maintained in good condition. Repointing, renewal of the flaunching and capping of unused pots should be carried out as part of the next cycle of external maintenance.
Construction and context
Chimney stacks are among the most exposed elements of a building, subject to constant weathering and requiring regular maintenance to remain watertight and structurally sound. On a house of this age the stacks are of solid brickwork and are unlikely to incorporate a damp-proof course, so they rely on the pointing, the flaunching and the flashings to keep water out. Uncapped pots allow rainwater into the flues, which can lead to dampness in the chimney breasts below (see E3 and E5).
Construction and context
As the stacks are shared with the neighbouring houses and form part of the main structure, their repair is likely to be a communal responsibility under the lease, with the cost shared through the service charge and, in part, with the adjoining owners.
Cause and likely repair
The open joints and cracked flaunching are the result of long-term weathering. Cement-rich mortars used in earlier repairs are harder than the soft stock bricks and tend to crack and shed water into the brickwork rather than away from it. Left unattended, water will enter the top of the stack and can reach the roof void and the chimney breasts. The likely repair is to rake out and repoint the stacks in a lime-based mortar compatible with the brick, renew the flaunching, and cap unused pots with ventilated cowls rather than sealing them. The flashings at the junction with the roof slopes should be checked at the same time.
Further investigation
One of the stacks sits directly above the chimney breast that has been removed within the flat (E5). Its support should be confirmed as part of the structural investigation recommended at E5 before any heavy work is carried out to the stack itself.