The uphill side needs a different detail
Run-off from the upper slope reaches the uphill side of the chimney. The back gutter or saddle detail must direct it towards the sides. Side flashings follow the roof slope and the front apron meets the tiles below. Assess these parts as one continuous drainage route.
Where is the water actually entering?
Damp beside a chimney does not prove that only the visible lead is defective. Check masonry joints, cracked corners, lifted edges, debris behind the chimney and concealed connections beneath the tiles. Request photographs of the suspected entry point before deciding on repairs.
Repair or renew the junction
An isolated defect may allow a local repair. Multiple splits, inadequate support or an incorrect drainage route can require reconstruction of the detail. Specify material, support, movement allowance and the masonry junction. Sealant along the visible edge does not automatically address the cause.
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Technical sources
Checked on 23 September 2026.