Loft condensation is increasingly common in UK homes — better insulation traps more moist air upstairs, and modern airtight homes have nowhere for that moisture to escape except the roof void. Here's how it shows up and how it's fixed.
How can I tell if it's condensation or a leak?
Condensation appears in cold weather, covers a wide area evenly, and gets worse overnight. Leaks appear during/after rain, are localised, and dry out between rainfall.
Will adding more roof vents fix it?
Usually yes — fitting 4–6 tile vents on opposing slopes creates cross-flow ventilation that clears moist air. £350–£600 typical.
Is loft condensation covered by insurance?
No — it's classed as a maintenance issue, not damage. But the cost of fixing it (vents, breathable membrane on re-roof) is much less than the timber repairs if left.
Blocked eaves ventilation
Loft insulation pushed tight against the eaves blocks the airflow path designed under the original roof.
Fit eaves ventilation cards or over-fascia vents; pull insulation back from the eaves at the perimeter.
Bathroom/kitchen extract venting into loft
Common mistake — extractor fans terminated in the loft instead of vented through the roof or wall.
Run flexible duct from the extractor through to a tile vent or wall vent.
Non-breathable underlayment
Old bitumen felt doesn't allow moisture vapour through, so any condensation has nowhere to escape.
Fit tile or ridge vents; on a re-roof, install breathable membrane (Tyvek/Permo).
Uninsulated, ungasketted hatches let warm moist air gush up into the loft every time someone walks past.
Fit a draught-sealed insulated loft hatch (£60–£150 + fitting).
Cold-bridging at the eaves
Insulation doesn't quite reach the wall plate, creating a cold strip where condensation forms first.
Pack eaves with insulation up to the wall plate while maintaining a clear ventilation path above.
Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.