Moved into a house recently have noticed that there is quite a severe damp problem in the loft. On cold days the whole of the underside of the roof is wet through to the point that it drips off the roof and soaks the insulation and is even coming through the ceiling in some places. Also the wooden beams holding up the roof are getting soaked so I'm quite concerned about them rotting.
House is a 1960's semi. The loft is insulated with fibreglass above the ceiling and the actual roof is a timber frame covered with felt and tiles in the standard way. What could be causing this amount of moisture? Is it just condensation and what can I do to solve the problem.