Why am I getting damp in a Relatively new house

Lack of ventilation. Possible roof leak. If it '80s build felt won't be breathable but probably that grey plastic. Hopefully not tar felt. What insulation?

Putting in the Insulation should fix the problem as the mould is telling you there are cold spots. However, you need to make sure that if they are laying new insulation over old that the old insulation is properly and evenly covering the plasterboard ceiling. Loft vents can only be a good thing but will make no difference to this. The other thing you need to be aware of is that the air qulaity inside the house is probably poor as chances are the ventilation is sub-standard. Again, the loft vents won't help. Finally, esp if the ventilation is insufficient, be aware that stopping the problem (correctly) on the ceiling may simply move the problem to the next coldest spot. We specialise in the ventilation side of this. The final part of the naswer may be your heating regime if this is being skimped too much.

To much installation could be a problem if not enough ventilation. Sounds like could be a possible leak in the felt! Would recommend checking the felt in Attic for possible damage

High levels of humidity or dampness in the home leads to black mould growth on walls and ceilings. Depending on the moisture involved, bedroom mould often begins in the corners of the room, where condensation is collected as it tries to exit the home. Poor ventilation is usually the cause.