Condensation and mould growth

Condensation in a property is usually a direct result of the ‘life style’ of its occupants. In other words it is how we live in our properties  i.e. the frequency, amount and type of heat used combined with what we do that produces water vapour that might eventually end up as condensation on windows and walls causing mould growth and a musty smell

The Problem
Condensation is by far the most common cause of dampness in buildings, probably accounting for most dampness problems reported. It affects both old and new properties.
Condensation is directly associated with mould growth, and it is this that the occupier first sees and gives an idea as to the potential scale of the problem. The mould is usually found on decorative surfaces, especially wallpapers, where it can cause severe and permanent spoiling. The mould and its spores (‘seeds ’) cause the ‘musty’ odour frequently associated with a damp house and can sometimes give rise to health problems.
The obvious places or condensation to occur are on cold walls and floors, but sometimes it occurs in roof spaces and in sub floor areas where there is a suspended floor. Timbers in these areas will become damp and susceptible to damage by dry rot or wet rot.

The Cause
It is a fact that warm air can hold more water as vapour than cool air. So, quite simply, condensation is caused when moisture-laden air comes into contact with a cold surface –the air is cooled to a point where it can no longer hold its burden of water vapour. At this point, (DEWPOINT), water begins to drop out of the air, and it is seen as condensation on surfaces. On impervious surfaces such as glass and paint, beads or a film of water collect, but on permeable surfaces such as wallpapered and porous plaster the condensing water is absorbed into the material. Therefore, the problem is initially not obvious.

Recognising Condensation
Condensation is very much a seasonal problem, occurring during the colder months (October to April). During the summer the problem is seen to go away. During the winter, ventilation of the house is usually low (windows and doors are closed, draught proofing takes place.) This allows build up of water vapour in the house, which, in some cases, is sufficient to cause condensation. So during the colder months the following signs begin to appear:

• Water droplets form on cold impervious surfaces such as glass and paint

• Slightly damp wallpaper (often not noticed)

• Development of moulds, usually black mould (Aspergillus niger). This frequently forms in areas where there is little air movement such as window reveals, floor/wall and floor/ceiling junctions, behind furniture against colder walls and in the classic triangular pattern in corners. Where the problem is very severe, water will even collect and remain on double-glazing.

In some cases, condensation may be long term but intermittent, forming only at certain times of the day or night. In these cases the only sign of condensation, may be mould growth, water perhaps evaporating during the day. One should also be aware that the problem can occur well away from the site of most water vapour production. For example, water vapour produced in a kitchen may diffuse through the house into a cold bedroom where it will condense on cool walls and lead to mould growth.

Mould growth (Aspergillus niger)
The greatest problem with long-term condensation is the associated mould growth, most frequently visible as black spot mould.
Mould spores are present generally in the atmosphere, usually at relatively low levels. Under normal circumstances they cause no problem, surfaces being too dry for their generation and growth. However, should they land on a wet surface (condensation) under humid conditions, then they will germinate and develop into heavy mould growth, with the inevitable release of vast numbers of spores. Not only does this cause decorative spoiling, but, in some cases, health of occupants may also be affected.
Note that Black Mould can only flourish on the pure water associated with condensation Black Mould is not an indication of rising damp

For a more in depth look at condensation you can visit www.specifypga.com

The Solution = Positive Input Ventilation (PIV)

A positive input ventilation unit gently supplies tempered, filtered air into a home using otherwise unused heat within a roof.




The benefits of this are enormous;

•    Firstly, it means that a significant proportion of external pollutants are prevented from entering the home.
•    Secondly, the use of the otherwise unused heat in the roof results in the ventilation unit providing a significant net energy gain to the home.
•    Thirdly, there is no better way to ventilate a home than from the inside out via a single, centrally located, supply air diffuser.

Drimaster 2000 The Drimaster 2000 is the UK's  leading Positive Input Ventilation unit

How does it work and how is it fitted

A good quality unit, fitted in your loft, will operate at an almost imperceptible noise level. A 300mm square ceiling diffuser is fitted in the ceiling (normally on the landing in a 2 storey house) and the unit itself is normally suspended from the rafters within the loft. You will hardly know its there .A variety of different units are available all with speed control to enable just the right amount of air input for the particular property. A properly designed and installed unit will ensure that old, contaminated, vapour laden air in your home is continuously diluted, displaced and replaced with good quality air. The result is improved indoor air quality and an environment in which condensation dampness cannot exist.

The old air exits through the thousands of air leakage points found in all homes. Indeed, positive input ventilation will even help to suppress unwanted infiltration (draughts).

The installation of a low energy positive input ventilation unit will ensure the air in your home is completely replaced with better quality air around 20 times a day. This is the recommended rate to maintain good air quality.


Energy benefits
Your roof is an energy source.

South east to south west facing tiles or slates absorb energy from the sun. Even the loft space itself is a substantial source of energy. During the heating season it will almost always be warmer than outside because of solar gain and conduction and convection losses from the home. Positive input ventilation units use the tiles/slates and/or the loft space itself to pre-warm the incoming air before delivering it into the home.

The input air enters your home at ceiling level, usually on your landing. This method re-circluates the warm air that rises and collects there as well as reducing the heat loss to your loft.

The slight pressurisation effect created helps reduce infiltration of unheated air through the leakage points found in all homes, having a consequential energy benefit.

In simple terms, a good quality low energy positive input ventilation unit will provide a significantly greater amount of energy into the home than the energy it consumes in the form of electricity, providing a considerable net energy gain. It is also worth noting that more energy is required to heat a home consisting of moisture laden air than one containing dry air.


But I don’t have a loft space!

The flat master above works in a similar way to the drimaster but is fixed to an outside wall and draws fresh dry air directly into the property via a 100mm duct. This makes this unit ideal for basements and small flats where a loft space may not exist or be available.


For more information on Positive Input Ventilation systems please visit  www.nuaire.co.uk  or call us for a free consultation and quotation