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Chimney Breast Damp in a Flat on North Grove, Highgate N6
A flat on North Grove in Highgate had damp showing on a chimney breast. The survey traced most of it to the way the chimney had been capped, which was trapping moisture inside the flue.
Project at a Glance
The Brief
The owner had staining and damp on the chimney breast and wanted to know whether it was rain getting in or something else.
The Survey
The chimney had been capped with cowls that were not vented. With no airflow through the flue, moisture inside it condenses on the cold brickwork and soaks through to the chimney breast, leaving hygroscopic salts behind. A small amount of mould was also noted.
The chimney stack itself needed some minor repointing. As the flat is leasehold, the stack is the freeholder’s responsibility, so this was flagged for them.
The Solution
Deal with the trapped moisture and the damaged finish:
- Fit a passive vent so air can move through the flue and moisture can escape.
- Damp proof the chimney breast to remove the salt contaminated finish.
- Pass the stack repointing to the freeholder.
The Work
The work was completed in a day on 29 April 2026.
The Result
With ventilation restored to the flue, the cause of the condensation has been dealt with rather than just the stain. Capped and unused chimneys are common in the period conversions around Highgate. See our page on damp proofing in Highgate.
Frequently Asked Questions
Why is my chimney breast damp?
Common causes are rain getting in through the stack, condensation inside a sealed flue, and salts left from years of coal fires. A survey separates them.
Should a capped chimney be ventilated?
Yes. A chimney that is capped at the top and blocked at the bottom traps moisture. A vent at the bottom and a vented cap let it dry.
Who repairs a chimney stack in a leasehold flat?
Usually the freeholder, as the stack is part of the building structure. Check your lease to be sure.
Damp on a chimney breast?
Our CSSW and CSRT trained surveyors find the real cause before recommending any work. Non-invasive survey with a clear written report. No obligation.
Project completed by Advanced Damp in Highgate, N6.
Sam Fitzgerald is the founder of Advanced Damp and a working damp and structural waterproofing surveyor diagnosing and treating moisture problems in residential and commercial properties across London and the South East. He is FODCS certified (a Federation of Damp Certified Surveyor) and a member of the Federation of Damp. His hands-on work covers rising damp, penetrating damp, condensation, basement waterproofing to BS 8102, and thermal imaging surveys, and he has personally completed over 400 damp surveys across properties of every type and age. Everything he writes draws directly from jobs he has carried out. He does not write about treatments, products or causes he has not dealt with first-hand in the field.
