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Roofing

Leaking roof when cold

Simon Boon 12/01/2026 - 8.42 AM

The ceiling under a flat roof has a slow leak when the weather is below freezing. The roof was pierced by a falling tile in 2020 and some water came in. This was repaired but since then small damp patches appear in cold conditions. This week there has been a small series of drips at the edge where the flat of the roof meets the down-slope. The roof itself is watertight and there is no leak from rain. How can I remove this excess water/ moisture from within the ceiling and ensure this is not an ice dam causing further leakage? Is it a roofing or insulation/ building issue? If physical repairs are required what is the typical cost range? House is a dormer type and was built in 2017 by private builder. Ceiling size is approx. 10m2 and the current leak along the 3meter edge where the flat of the ceiling meets the slope of the rest of the roof.

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7 Answers

Cannon Builders

Rating: 4.9 out of 5
Redruth
It could be condensation, if it only appears in cold weather when you have heating on, maybe you need to check if you have enough airflow above the insulation?
Answered7 January 2026
2

HRD Roofing and Building

Rating: 5 out of 5
Hampton
I also would say most likely cause is condensation. Improve air flow
Answered7 January 2026
1

Andrew burton flat roofing

No reviews yet

Sutton In Ashfield
Try running a dehumidifier in the room see if it improves if there is any water trapped in the system the only way to get it out would be to cut a hole in the roof at the lowest point and get a wetvac in then repair the area however this will only work if you have a warm roof
Answered8 January 2026
1

Architronica Limited

No reviews yet

Hornsey, London
This is probably caused by moisture in warm indoor air freezing inside the roof where the flat and sloped sections meet, not by rain getting in, and it is usually fixed by improving insulation, sealing air gaps, and making small repairs at that roof junction.
Answered8 January 2026
1

Watertight Roofing Specialists

Rating: 4.8 out of 5
Bognor Regis
You will need flat roof ventalation mushroom heads and soffit vents installed hope this helps
Answered12 January 2026
1

sandeep singh

Rating: 4.9 out of 5
Hayes
Based on the information provided, the roof covering itself appears to be watertight and the issue is unlikely to be caused by rain penetration. The symptoms described are consistent with condensation forming within the ceiling/roof structure, most likely due to insulation gaps, thermal bridging, or an incomplete vapour control layer at the junction where the flat dormer roof meets the pitched roof. In cold or freezing conditions, moisture within the roof void can accumulate or freeze and then release as drips when temperatures fluctuate. This is therefore considered a building fabric and insulation issue rather than a roofing defect. The recommended solution would be to allow the affected area to dry and to improve insulation continuity, vapour control, and ventilation where required. Localised opening of the ceiling may be necessary to carry out these works.
Answered12 January 2026
1

Anonymous user

You will need some mushroom vents on the roof and soffit vents in the soffit to generate air flow as the problem is most definitely condensation.
Answered12 January 2026
1