bad damp after having new soffets and facsia

[mickopara]

I had new soffets and facias at the end of last year, the lad also came back and rebedded my ridge tiles as the mortar had worn away, since then ive had bad damp coming through on the ceiling above the window where the ceiling slopes down on both front bedrooms.
The facia guy has been back and cant see anything wrong but it clearly started after the job had been done. It only seems to be bad when it freezes outside, theres no damp patches when it rains.
There is however mould growing now and its spreading.
The only thing i can think of is ventilation, or lack of it and my old ****ty facsias were letting enough air through and the new ones arent.
Any ideas would be greatly appreciated.

 

[oilman]

Were the old ones wood, and the new ones plastic?

 

[mickopara]

yeah wood, the old ones were the originals i think, 1950s. The new ones are plastic and they did strip away the old instead of capping over it.