Why is there damp in my loft?
Loft damp can result from an external roof leak, but condensation is also common. Warm moist air entering a cold roof space, poor ventilation and insulation issues can produce wet timbers or felt that homeowners mistake for a leaking roof. Correct diagnosis is important because the remedies are different.
Leak, condensation or both
Damp in a loft has two broad causes: water getting in, or moisture generated inside the house condensing on cold surfaces. They can look similar and they sometimes occur together, but the fixes are different.
Water ingress tends to be localised and linked to rainfall, often near a chimney, valley or roof window. Condensation is usually more widespread, worst in cold weather, and shows on the underside of the roof covering or underlay.
What an inspection checks
A roofer will look at the pattern and location of the damp, the condition of the covering and details above it, and whether the roof space is ventilated as intended — blocked eaves, sealed vents and insulation pushed into the eaves are all common findings.
Establishing the cause first avoids the common outcome of repairing a roof that was not leaking, or improving ventilation on a roof that was.