Condensation & Black Spot Mould

Condensation (Black spot Mould)

Condensation is an extremely underestimated cause of damage to buildings which is responsible for rot in roofs, floor joists, window frames and many other areas of our homes. On walls condensation problems often lead to blackspot mould which is as it sounds - a black spotted mould growth, It is particularly prevalent on cold areas of walls and ceilings. Another product of condensation can be mildew, mildew can be a white or beige coloured mould which looks almost like a fine pale fur. Mildew is often found in cupboards and wardrobes and on the clothes stored in them. These moulds which have usually resulted from the effects of condensation can affect our health and can cause or aggravate Asthma and other ailments. People with weak or compromised immune systems can also be affected, this is because of the millions of spores these moulds release into the atmosphere within our homes and buildings and which we subsequently breathe in.

How to identify condensation

It is not always easy to tell what condensation is, but other kinds of damp such as leaks from plumbing, spillage and floods, usually leave a ‘tidemark’. Condensation is usually found on the interior of external north facing walls, in corners, in cupboards and under work surfaces – in fact wherever there is a cold or cooler surface and little air movement.

If you live in a new or recently modernised property, don’t forget that it will take time to dry out after building work. It can take 9 to 18 months drying time. After a source of moisture ingress has been corrected the times for drying out of walls etc are similar. Usually more heat and ventilation will be required during a drying out period.

Condensation Black Spot mould
Condensation mould

What causes condensation

Condensation is caused by water vapour. All air contains water vapour. The quantity of vapour contained is dependant on the temperature of the air. This ratio is called the relative humidity. Hot air is able to carry much more moisture than cold air, so as the temperature of air rises, it expands thus containing a greater volume of vapour within.

As soon as warm air, containing vapour, hits a cooler surface, it will condense. This is most obvious on windows and wall tiles (which usually have a cooler surface), but this can also happen on damp or cold walls and ceilings, it is often worse on certain decorative finishes. Because warm humid air generally condenses on cooler surfaces we need to let the humid stale air out and bring some fresh air in.


Ventilation is the key to reducing condensation. There are many ways we can deal with symptoms or effects of condensation, but only one way to deal with the cause. We must ensure the building is dry and adequately ventilated.

Condensation tends to manifest itself in the corners of a room or behind furniture etc against colder walls (often north facing) where there is less air circulation.

Moisture forms on the surface of the walls/ceilings and creates a damp area; this can even penetrate some surfaces. The fungal spores (which are constantly in the air all around us) come into contact with the dampness which gives them the ideal conditions to propagate and develop into the various moulds.

Condensation mould is usually formed in spots and patches; these patches tend to have a blackish appearance which is why they are termed 'Black Spot Mould'. This can cause irreparable damage to decoration and furniture, sometimes occupants can develop chest or breathing complaints if a condensation problem goes uncorrected.

Finding the solution to condensation

Once you have eliminated all the obvious sources as mentioned above, if the problem still persists, we primarily need to introduce more ventilation, it is however important that we introduce the correct type of Ventilation for your property type and circumstances. Mechanical ventilation may need to be installed.

These ventilators come in many different forms, some are more effective than others. Heat recovery ventilation systems will take in fresh air from outside, pass it through a series of interconnected chambers warmed by the outgoing air (similar to a car radiator in reverse) so that you are introducing heated air into your home and not pumping warm out and cold in which could affect your comfort levels and heating bills. Other types of unit, especially PPU's (positive pressure units) can increase the internal pressure of the property thus driving the stale humid air out.

For more info on these units and the pros and cons of the different types or which one will be more suited to your particular circumstances you will need to arrange an inspection from one of our experienced surveyors (click here). They will offer free advice and can either arrange everything for you or we can offer a supply only service where you can buy a unit from us and arrange fitting yourself using our DIY options available through our shop (click here).

Call and book your free visit for help and advice

If you think you have a problem and would like some expert advice why not talk to a fully vetted and accredited Which? magazine TRUSTED TRADER where you know you will receive an honest and fair appraisal of your problem and a highly competitive price if any work is needed!

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Whatever your thoughts, questions or concerns may be, everything starts from a first step, the first step in this case is to get in touch, we will send a friendly helpful surveyor to you. You are then free to run your thoughts and ideas past him, he will sit down, chat with you and tell you whether what you want to do is practical and possible, if there are any more practical or cost effective alternatives you may not have thought of and give you an approximate cost for your project. We realise you may need a little help to decide what is possible, so we provide this service free of charge and with no obligation - except perhaps a coffee while we chat!

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