Possible causes
- Poor roof ventilation
- Warm moist air from bathrooms or kitchens venting into the loft
- Non-breathable underlay on older roofs
- Insulation blocking eaves vents
Warning signs
- Droplets on the underside of the felt in cold weather
- Black mould on rafters
- Damp that appears without rain
Typical solutions
- Adding roof or eaves ventilation
- Re-routing extractor fans outside
- Breathable membrane when re-roofing