Damp insulation loses most of its thermal value and can lead to mould and timber problems. The insulation itself is rarely the cause — it is usually a symptom of moisture entering the loft or being unable to escape.
On this page
- Signs to look for
- Common causes
- Fixing it properly
Signs to look for
- Insulation that feels heavy, cold or matted rather than light and springy
- Dark staining, mould growth or a musty smell
- Water marks on the underside of roofing felt or on rafters
- Droplets or frost on nail points inside the roof on cold mornings
- Damp patches concentrated near the eaves or under a bathroom extractor route
Common causes
- Blocked eaves ventilation, often caused by insulation pushed into the edges
- Bathroom or kitchen extractor fans venting into the loft instead of outside
- Roof defects such as slipped tiles or failed flashing
- Warm moist air rising through an unsealed loft hatch and gaps around services
Fixing it properly
Replacing wet insulation without addressing the moisture path guarantees a repeat. Our standard approach includes lap vents where the roof needs them, insulation kept clear of the eaves, and a draught-proofed hatch — included rather than charged as extras.
Common questions
Does damp loft insulation need replacing?
Insulation that is persistently damp or mouldy should be removed and replaced, but the ventilation or moisture source must be corrected at the same time.
If you would like an honest opinion on your own loft, send us your postcode and a few photographs. Most lofts can be assessed and quoted remotely using satellite imagery, and we will tell you if work is not necessary.
Related: Do lap vents actually work? • Price list • Project planner • Contact