Which profession best to advise on mould

[meathman]

From September until May we have issues with mould on ceiling of North facing bedroom and bathroom. Mould run in a line where ceiling meets external wall. Have added vents, tried dehumidifiers, opening windows etc. Has not improved. Would like to get appropriate professional to advise on next steps. I'm not sure what is the appropriate profession to contacte.g surveyor, engineer, architect. Can someone advise please?

 

[Micks'r]

Building physics is the general discipline you are seeking.
The cause of your issues is an imbalance somewhere in the heating/ventilation/moisture load equation. To get to the bottom of what's going on and pinpoint the true cause I usually recommend automatic logging of the temperature and RH% levels over a period of a couple weeks in addition to a visual and other survey techniques such as thermal imagery. Note, activities and issues in the non effected areas of the house also often have a role to play and need to be taken into consideration too.