How can I tell the difference between condensation and a roof leak?
The short answer
Timing and pattern separate them. A leak follows rain, appears in the same place each time and leaves a defined stain. Condensation follows cold weather and household humidity, spreads over a broad area, is often worst near the eaves and on the coldest surfaces, and can appear during a dry spell.
What evidence should you look for?
Damp present after a cold, dry night with no recent rainfall.
- What it can mean
- Condensation rather than ingress.
- What else could explain it
- Melting frost or snow on the roof can produce water entry without rain being recorded.
Monitor
What could this mean?
Keep a short log of dates, weather and where the damp appeared. Two or three entries usually settle the question before anyone climbs a ladder.
What this evidence cannot tell you
The two can occur together, and a roof with poor ventilation and a small leak shows features of both.
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What should you do next?
Log weather against each occurrence for a few weeks, and check whether extract fans and eaves ventilation are working as intended.
Reviewed by Aaron, Owner, Elite Roofing Services Cumbria Ltd — last reviewed .