New build garage mould help

Hi all,


Been living in my new build for just over a year now.


When I moved in I painted the garage walls with white masonry paint and fitted rubber tile matting to the floor.


I have plastic/mdf shelves which are covered with mould along with suitcases stored in the trusses. There isn't much else in there other than kids toys and bikes, nothing that will bring any wet in. There is no sign of wet or damp anywhere.


It's a pitched roof garage with side access door and an up and over door. I would of said there was airflow due to the gaps around the trusses (see daylight) and the gap under the garage door.


Im Not quite sure why I've got it.


What can I do to stop/prevent it?


The garage will be used for dog grooming shortly which will obviously put more humidity into the air with the shower.


Will plasterboarding all the walls and roof help or does the mould need sorting prior to this?


Any help would be appreciated, thanks.

 

Whats the source of dampness?