2 years ago we had a new slate roof to our 1930's bungalow with tyvek underfelt.No soffit or ridge vents were fitted, we were told tyvek is breathable and vents not required. During frosty weather significant condensation occurs on underfelt, dripping on to loft insulation. Dupont/Tyvek surveyors have visited and told me to seal eaves by pushing insulation in hard. Condensation is now worse. In addition condensation now drips through roof of dormer (flat bitumen roof) staining carpets. Will vents solve this problem. Do I need batten cavity vents as well? Does anyone else have experience of tyvek? Help?