New Ventilated fascia's - now condensation problem..

[anonymous-user]

Hi, I have a problem which I hope someone can advise on.
My house is 40 years old, the walls are brick-cavity-block-plasterboard dabbed on. Cavity wall insulation a year ago, all OK.
1 bedroom has an angled ceiling along 1 wall, where roof cuts into the room. I guess this part is plasterboard-gap between rafters-Plastic Felt-Roof tiles.
Funny design..

Anyway, a month ago I had new fascias fitted, proper job, ventilated along whole length. Probably next to no ventilation before.
Now this angled part of the ceiling & the top of internal wall is dripping in condensation. No problem anywhere else. Most walls are warmish to touch, the top of that wall & the angled ceiling are ice cold. So I suspect that there is a gale blowing through the gap due to new ventilation. On the few occasions that the temp has climbed above a few degrees recently, it is OK, even when raining.

So my theory is that I need to insulate that area, easier said than done due to shallow roof angle etc. I had a couple of ideas..

1) Wickes sell 2'' thick polystyrene sheets. So I could cut to size & feed down the gap between the rafters. To block airflow & give some insulation.
2) As above but also drill holes along top of dabbed on plasterboard & fill with expanding foam..

Or neither of the above if there is a better way!

Ideas?

[Stegel]

I'd recommend the first option - use a rigid board insulation, cut to as tight a fit as will allow the sheets to be installed, pushed down between the rafters, preserving a ventilation pathway above the insulation. Depending on the rafter depth it's unlikely you'll get very many inches in the space less a ventilation gap, so I'd suggest using a better insulant than EPS - a Kingspan or Celotex PUR or phenolic foam board, with the foil facing adding to the insulation performance.