White mold in the attic?
I had 2 builders come out to survey and both pointed out that I had recently reinsulated the loft. The issue was that there was no ventilation in the loft so the damp air was trapped up there by the new lovely fat insulation I had installed. The solution was to install roof vents to allow some airflow in the loft.
It cost me about £1500 to get this done but that included some remedial work to the chimney to try and address a penetrating damp issue in one of the bedrooms.
It's been about 6 months and I was told it would take some time to clear up so I'll recheck it again in the new year.