Fungi/Mould Inside Wall-Vent Hole

The vent that should be used is known as a passive vent. This has some lambswool internally to prevent draughts whilst still allowing air to circulate. Whilst most damp proofing companies can fit these vents ( and do in the course of their works) for an individual fitting I would ask a general handyman to fit it. Important NOTE: Vents to address condensation and high internal moisture levels should NEVER be fitted at low level. Many so called "damp experts" misinterpret air vents for controlling sub floor ventilation with air vents controlling condensation.

Top answer from Shaw. Thank god someone who knows what they're talking about.👍

Good straight answer. And totally correct

I would have to research the building in order to double check that the walls have not been filled with insulation which can cause serious damp, the air vents can be changed with ease but will only solve the issue if all wall cavities are substantial.

I'm not saying the answers wrong but I would investigate whether there is ingress through a fault in the roof after that's eliminated then I would look for the failing in the vent itself

Black spot mould requires a relative humidity of 65% or higher to flourish. The humidity is relative to the temperature so the lower the temperature, the higher the humidity , within normal living conditions in the UK. The wall vent is exposed to incoming and out going air , the out going air is moisture laden and the vent will always be a lower temperature than the property interior temperature. This causes condensation and high relative humidity within the vent - black spot mould will flourish. Replacing the vent with a new one will make no difference to that condition. Passive vents are not ideal ventilation because one has no control as to the direction or the quantity of air flow ; it may even reduce the interior temperature and cause condensation with black spot mould ! Mould is a mucus membrane irritant and may cause chest problems and headaches for some . Mechanical extraction is always the best method .