We recently bought a 1970,s bungalow unmdified until now. We are experiencing condensation in the loft?

The condensation has frozen on the roof felt then thawed and droplets wet the loft and goods stored there. Prior to this their was only the old insulation, we have added new insulation and wondered if this will see the end of the problem. The new shower extractor and boiler flue p through the loft but are all in tact and not "leaking" in any way.My wife thinks the emission form the flue could be being blown back against the roof tiles(from outside) or even under and back into the loft causing this problem,Any istance would be gratefully received, regards Stuart