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Damp around vent in external wall

Posted by Laura Barley, on
I had vents installed in the walls of my flat to increase ventilation and thus reduce condensation however a damp ring has now appeared on the wall around the vent. Any suggestions on how to fix this?!
Peter Barber

Peter Barber

Hi Laura. Condensation is caused simply by too much humidity being created, and not enough ventilation to take it away. Other factors such as sufficient heating is quite important. Condensation is the most common form of dampness found in properties and the method of successful control is to reduce the relative humidity to an acceptable level. Mould can only grow in properties that suffer with a relative humidity level persistently above 71%. The problem is that in some cases negative ventilation can cause as much condensation as no ventilation at all.... Condensation is temperature driven. Therefore when warm humid air comes into contact with a cold surface. The water in the air will condense on that surface. If you are ventilating an already cold room, then the temperature will be lowered therefore raising the relative humidity leading to more condensation and mould. This is known as negative ventilation. You have two options to control this. 1. Install humidity controlled fans to only to water making areas. Kitchen and bathroom. These fans are preset at around 60% RH which means that they will activate automatically when this level of humidity is reached. 2. fit a positive pressure fan to the loft area. These appliances has shown remarkable results in the control of condensation. The information on the fans can be found on the Nuaire website. Just search for Dri-master for the positive pressure fans, or Genie for the wall mounted extractors. You will need an electrician to fit either appliances so you will need to post your job into that category. I hope that this helps. Best Wishes. Peter Barber CSSW.,.CRDS. London Waterproofing Solutions.

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