Condensation dripping from felt in loft

locky123

Moved into a detached house last year. Pitched, tiled roof, built early 1970s, cavity wall, air bricks below DPM. No cavity insulation.

Last winter noticed condensation dripping from inside of original felt in the loft. Looked at eves to check there was an air gap between insulation and roof and all was OK. Previous owners had put extra insulation across rafters. It was very cold in the roof space. Checked for ventilation outside and saw that the back of the house had a few round vents in the plastic soffits. But at the front there were none, they were original soffits. So fitted a round vent between each rafter front and back last winter, hoping that this would cure the condensation.

However the condensation is back in the roof now the temps have dropped to below freezing at night.

Do I need more ventilation? If so where? In soffits or at gable ends or vented ridge tiles? Or replace felt with breathable membrane? Concerned that the condensation will lead to rot in the rafters.

The condensation is across the whole of the roof, worse on north facing side. There is some space around the loft access where we have boxes, which we now changed to plastic as cardboard was getting damp.

Bathroom and en suite have ceiling extractors. I changed the flexible ducting to rigid with condensation trap, which drains via pipe to outside. I checked all pipe joints and they all sealed. Bathroom has GU10 downlighters x4, but not sure whetehr they can be sealed. Purchased a dehumidifier last month which helps with condensation inside.

llandyrnog

Vented ridges should help if the soffit vents are clear, this would introduce a cross draft to help dry out the trusses or rafters. You say there are airbricks at low level in the walls and no cavity insulation, could warm moist air be travelling up the cavity and condensing on the cold felt in the roofspace ?. Cavity Insulation could help. What it the depth of the existing loft insulation ?. For condensation to form, moist warm air comes into contact with a cold surface, so a continious vapour control barrier such as a visqueen could be installed under the loft insulation to stop that warm moist air reaching the cold surface.

tony6403

Unlikely to be caused by air movement in the cavities as these will very likely be closed at the top. The airbricks below dpc don't vent the cavity; in one piece (or more recently in telescopic form),they go right through the walls to ventilate the floor structure.
Have you closely inspected your loft hatch door? Is this fully insulated and within reason airtight?

Hintza

We built stables this year and as you can imagine there is plenty of air (top of doors open 24/7) but since the cold weather and more importantly lack of wind has arrived then roof is dripping.

My thought would be is wait until we get a few days of decent breeze and then have another look. You are just taking a snap shot in cold weather at the moment.

Of course if it is blowing a gale where you are then ignore everything I have said!