My loft insulation is wet — what do I do?
Wet insulation does not insulate, does not reliably dry out in place, and is telling you something is getting water into the loft. Find the source before replacing anything.
- Difficulty
- beginner
- Time
- 45 min
- Read
- 2 min
- Safety
- caution
Short answer
Find and fix the water first — a roof leak, a blocked gutter overflowing back, condensation from blocked ventilation, or a leaking tank or pipe. Then remove the wet insulation rather than waiting for it to dry, because saturated mineral wool stays wet a long time, loses its loft and can grow mould.
The insulation is the symptom. It is also a useful diagnostic, because where it is wet tells you a good deal about why. A patch under a specific point suggests a leak above it; a broad area near the eaves suggests condensation or water tracking in at the roof edge; wet under a tank suggests the tank.
Safety
Step by step
- Find where the wet area is and what is directly above it.A defined damp patch usually has a cause immediately above: a slipped tile, a nail hole, a flashing, a valley, a soil vent penetration. Look up before looking anywhere else.
- Check the tank and any pipework.An overflowing tank, a weeping valve or a split lagged pipe soaks insulation from above without any roof defect at all.
- Consider condensation rather than a leak.Insulation damp across a wide area, particularly near the eaves, with mould on the underside of the roof and moisture on nails, is condensation. That means air movement from the house and blocked ventilation, not a hole.
- Check whether the eaves ventilation is blocked.If it is, the loft cannot dry, and any moisture arriving from the house stays. GuideHQ has a guide on keeping the eaves clear.
- Remove wet insulation rather than leaving it to dry.Saturated quilt holds water for a very long time against the ceiling, stays compressed, and can grow mould. Bag it and take it out.
- Let the ceiling and timbers dry before replacing it.Putting new insulation over a wet ceiling traps the moisture. Give it time with the loft ventilated.
- Check the ceiling below for damage.Plasterboard that has been wet may be soft, stained or sagging. That is a repair in its own right and a safety issue if it is bowing.
- Identify the insulation before disturbing it if the house is older.Very old loft insulation is occasionally something that should not be disturbed. GuideHQ has a guide on that question, and it is worth reading before pulling anything out of an old loft.
Questions people ask
Can wet insulation be dried and reused?
Lightly damp quilt in a well-ventilated loft may dry and recover. Saturated or long-wet quilt generally does not regain its loft, and replacing it is cheap relative to the effort of trying.
How do I tell a leak from condensation?
A leak is localised and worst during and after rain. Condensation is widespread, worst in cold weather, and usually accompanied by moisture or mould on the underside of the roof rather than a defined wet patch.