damp around air brick

[Mr Fix It]

afternoon all,

ive recently had a damp problem at a the vent cover in one of my rented houses. ive used a damp metre and its quite high around the plastic grill.

On the outside external wall, it looks very wet around the air brick in the wall, but no obvious sign of where from? gutters above are water tight, no pipework around or anywhere near the brickwork?! im a bit stuck as ive had the mould cleared and treated for my tenants, but the damp meter still picks up damp and theyve called me to say their having to clean it off daily?

its a ground floor studio, vent is clear and the room has a radiator. No other walls or areas are affected at all?

its not been raining at all so...help?

 

[noseall]

was there a square plastic conduit used in conjunction with the air vents?

if so, this conduit will need to slope slightly towards the outer course of bricks.

if it slopes inward then water ingress can be a problem.

 

[Mr Fix It]

this may sound stupid, but im not sure what you mean? sorry

 

[noseall]

is the property cavity wall or not?

 

[Mr Fix It]

yep.

 

[noseall]

the conduit or duct is a piece of round or rectangular plastic or terracotta tube linking the external airbrick across to the internal louvred vent.

this is so no air is lost into the cavity and to prevent any loose fill cavity material from clogging up the air vent.

 

[Mr Fix It]

i getcha. so i can take off the vent cover on the inside, stick the torch through and hopefully see the cause?

 

[JohnD]

i would be thinking about condensation from moist air in the room hitting the cold ventilator, especially if it has been closed or blocked to prevent airflow

or rainwater running in from outside

or a leaky pipe or gutter above it.

Holes in walls (especially cavity ones) should always have a piece of plastic duct inside to line the hole, and it should tilt outwards so condensation or rain do not run into the house. older houses may have a terracotta, metal or slate liner.

edited: noseall knows all