Loft condensation: ventilation, not leaks
Damp loft timbers, mould on the underlay and drips in cold weather with no rain are the classic condensation picture. Chasing it as a leak wastes money.
Where the moisture comes from
Warm, moist air from the house — bathrooms, kitchens, drying laundry — rising through gaps around loft hatches, downlights, pipe penetrations and service runs.
How ventilation fixes it
Airflow at the eaves and at high level moves that moist air out before it condenses on cold surfaces. Both ends are needed; ventilation at only one is much less effective.
What blocks airflow
Insulation pushed hard into the eaves, solid soffit boards with no vents, and packed-out roof spaces during loft conversions. Over-insulating the eaves is a very common own goal.
Ventilation options
Soffit vents, over-fascia vents, tile and slate vents, and dry-ridge ventilation. Which combination suits depends on whether the roof is cold or warm and what the soffit detail allows.
Fix the source too
Sealing the loft hatch, ducting bathroom extractors to outside rather than into the loft, and closing service penetrations reduces the moisture load in the first place.
FAQs
If the damp appears in cold weather rather than after rain, and it's spread evenly rather than in one spot, condensation is more likely.
They reduce risk but do not universally replace ventilation. It depends on the build-up and the product specification.
Yes — tile vents, over-fascia and soffit vents can normally be retrofitted without stripping the roof.
Related reading
More on materials & systems and the jobs that usually come with it.
- Insulating a flat roof properlyMaterials & systems
- Warm roof vs cold roof constructionComparisons
- Access, neighbours and awkward propertiesProcess & paperwork
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
Get a fast quote
Family-run and Hampton-based. Tell us what you're seeing on the roof and we'll come and look properly before quoting.