Mould on Walls & Ceilings, Damp Walls?

Have you got black mould on the walls and ceilings?

A mould issue can often be misdiagnosed and can have several causes. You can go into a lot detail on this subject matter, but very generally…

Mould is often caused by:

Too Much Moisture:

This first item is straight forward. When there is too much moisture inside a building and it can’t escape, mould will form. Moisture needs to escape from bathrooms, cooking and living areas (things) inside the house. There is a lot more to this subject, but this is just a quick overview.


  • Buildings need good ventilation to prevent build up of moisture. Hence kitchen, bathroom fans, etc.

Water Ingress:

Linked to above. If there is water ingress, (rising damp, water penetration, leak in the roof, etc). Then there is an extra need to get rid of the additional moisture.


  • Stop the water ingress, so the area can dry out.

The Dew Point:


This is the one that gets missed and mistaken, (misdiagnosed) as water ingress. Home owners, (and the specialist’s they employ) can spend a lot of money thinking the mould is caused by water ingress, when the dew point is the reason. Basically, a lot of homes are heated more these days (central heating, etc), when they may have originally only had an open fire.

When warm air hits a cold wall or ceiling, water droplets form. The wall or ceiling then becomes damp and mould starts to form. This is often mistaken as water ingress.

This is often caused by:

  • Heating.
  • No additional insulation.
  • or, too little insulation.

Solid Walls and Thermal Bridging:

Often the cause of issues with the dew point…

Thermal Bridging:

Also called a cold bridge, heat bridge, or thermal bypass…

A thermal bridge is where there is a higher thermal conductivity (usually more than that of the surrounding area). I.e. Cold can be transmitted past any insulation that may be in place, (insulation can be anything that helps stop the heat escaping, they just have different levels of efficiency). This can cause condensation to form where the hot air meets the cold bridge. Mould can then start to appear. The answer is to remove, stop any thermal bridging, increase the level of insulation and move the dew point further away (may not be the correct term, but it kind of explains it).

Solid Walls:

Can cause issues because they can directly transmit the cold through the wall, or the heat in the other direction. The thickness of a solid wall also has an effect. The thicker the wall is, the more insulation it may provide, (though it may still be poor dependant on the material used in the wall).


  • Solve condensation, by increasing the insulation levels and stop thermal bridging.
  • You could also increase the heat, so the cold wall is not cold anymore. I’ve seen examples where the radiator thermostats are removed and the heating is left on 24 hrs. Not practical, cheap, or environmentally friendly!


The more you insulate and seal a building (reducing ventilation), the more the moisture levels can increase. It’s all a balancing act.

Hope this helps someone… 😃

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