Loft Condensation in Winter: Is It a Leak or Something Else?
Every winter we get calls from homeowners who've found water in their loft and assume the roof is leaking. Sometimes it is. But just as often the culprit is condensation: warm, moist air from inside the house rising into a cold loft and turning back into water on the coldest surfaces.
Why condensation gets worse in winter
In winter we heat our homes, dry washing indoors, take hot showers and keep the windows shut. All of that moisture has to go somewhere. When it reaches the cold underside of the roof, it condenses into droplets, much like water on a cold window.
Condensation or a leak? How to tell
- Condensation shows up as droplets spread across the underside of the felt or membrane, often widely
- Leaks usually show as a localised wet patch or stain, often below a chimney, valley or damaged tile
- Condensation is worst on cold mornings, even when it hasn't rained
- Leaks get worse during or straight after heavy rain
- Frost on the underside of the roof on very cold days is a strong sign of condensation
Common causes
Older roofs often have non-breathable bitumen felt underneath the tiles, which traps moisture. Insulation pushed right into the eaves can block airflow, and bathroom or kitchen extractor fans that vent into the loft instead of outside add a lot of moisture.
How to fix loft condensation
- Make sure extractor fans vent outside, not into the loft
- Keep the eaves clear of insulation so air can flow
- Add tile vents, ridge vents or eaves vents to improve ventilation
- Seal gaps around loft hatches, pipes and downlights
- When re-roofing, use a modern breathable membrane that lets moisture escape
When a re-roof is the right answer
If your roof still has old felt and condensation is a constant problem, a strip and re-tile with a breathable membrane and new battens solves the issue at its source. It's exactly the kind of work you can see in our gallery.
Not sure whether it's condensation or a leak? We'll take a look and tell you honestly. Call 07337 682 151 to book a free roof survey.
