Water entering a roof lands on a rafter, runs along it, drops onto the ceiling joists, tracks sideways, and finally soaks through at the lowest point it reaches. The stain you can see is frequently two or three metres away from the hole. That is why guessing costs money.
Three quick tests
- Does it change with the weather? A stain that grows during or shortly after rain is water ingress. One that appears on cold mornings regardless of rain is condensation.
- Does it change with usage? A stain that spreads after showers or laundry, with no rain, usually points at a plumbing leak or moisture-laden air escaping into the loft.
- Is it clean or dirty? Roof-water stains are typically brown-edged and ringed because the water has picked up dust and debris. Clean-water plumbing leaks often stay pale.
Condensation is more common than people expect
Well-sealed modern homes with poorly ventilated lofts produce interstitial condensation on the underside of the felt, which drips onto the insulation and shows on the ceiling. Look for uniform dampness across a large loft area and moisture beads on nail points, rather than a single wet run down one rafter.
What to check in the loft
- Wet or dark staining running down a specific rafter — follow it up to its highest point.
- Daylight through the underlay on a bright day.
- Damp insulation directly beneath a valley, chimney, vent or soil pipe penetration.
- Any smell of damp timber, which suggests the ingress is not new.
Confirming it from above
Once you have narrowed down the internal evidence, a close-range photographic survey of the corresponding elevation usually settles it. We photograph each elevation, circle and grade every defect, and give you the report within about 24 hours — so you can hand a roofer a location instead of a mystery. £99 residential, £149 commercial.