Every year around late autumn another seasonal event takes place without fail. Windows start to steam up, mould growth starts to grow and you know condensation is back with a vengeance.

In the colder months condensation will occur somewhere in nearly every property; housing, commercial or industrial, unless appropriate remedial precautions have been taken. It is the largest single complaint received by landlords in both the public and private sectors, and can cause serious health problems to the owner-occupier.

The Problem

Condensation is caused when warm, moist air meets a cold surface and the water vapour "condenses" out.

The capacity of air to hold water is related to temperature; warm air holding more water than cold air. Air is saturated when it cannot hold any more water vapour at the existing temperature and therefore has a relative humidity (RH) of 100%. If the temperature of the air falls until saturation point occurs, the air is at a critical temperature or dew point where any further fall in temperature will result in water vapour being forced to condense out as liquid water.

The condensed water usually appears as droplets on windows and other non-absorbent surfaces. This is surface condensation; it is fairly obvious and always occurs on the surfaces which are at or below the dew point of the air.

The water vapour inside a building also contributes to a greater overall air pressure. This results in the outward movement of warm, moist air through the structure of the building. This may eventually cool below its dew point within the fabric of building resulting in interstitial condensation.

Interstitial condensation is more complex than the surface form and presents a greater hazard. It can go undetected for long periods until serious damage has developed such as timber decay.

There are four main and interrelated factors which affect the occurrence of condensation in a building:-

 

Moisture generated within the building
The ventilation system provided and use made of it 
The heating provided and use made of it
The thermal capacity and insulation

The first two factors are normally the primary causes because moisture generated by domestic activities can be significant and the fact that most buildings are effectively sealed to prevent heat loss means there is no background ventilation to allow the moist air to naturally filter out of the building. Features such as double glazing and draught excluders cause problems associated with poor air circulation, which can lead to stale air as well as condensation.

Condensation is quite often found in kitchens and bathrooms, however warm moist air can also spread to cooler parts of the building such as bedrooms to condense on any cold surface. Here the first signs to the occupier will be mould growth.

The appearance of mould creates concern about damage to furnishings, decorations, unpleasant smells and possible effects on health.

Surface condensation can be determined if RH, air and wall surface temperatures are measured. This can be achieved at the same time using either air/surface thermometers and/or various instruments such as thermo hygrometer, digital hygrometers or in some cases simply dew tabs.

Even if conditions are changing at the time of surveyor the survey is made under hostile conditions, the risk of surface condensation can still be evaluated if RH and wall surface temperatures have been determined.

Unlike surface phenomenon interstitial condensation cannot be measured directly and only the risk of its occurrence can be assessed.

Site record sheets are invaluable in this type of survey, as specific data has to be recorded. In fact some forms do allow an estimate of costs to be made quickly which will save time and money.

Low risk

Isolated mould growth but no obvious signs of condensation. You will find this quite often on "call backs" during or after drying out following replastering. The answer here is the use of anti mould paints (available in kit forms for sale to householder) to prevent mould growth.

Medium risk

Mould growth and condensation in kitchen/bathroom and some other rooms. Apply biocidal washes, anti mould and anti condensation paints and install ventilation products. There are various options with ventilation products from passive ventilators (air bricks, black holes), local extraction fans and PIV

(Positive Induced Ventilation).

A habitable room should be ventilated so that all the air is replaced at least once every hour. Air replacement in high risk rooms such as bathrooms and kitchens should be much greater than habitable rooms. Building Regulations now recommend that this is achieved by having permanent ventilation of at least 8000mm2 (equivalent to a 4 x 4" hole in an outside wall) and rapid mechanical extraction in high risk rooms.

High risk

Severe mould growth and condensation throughout the property.Essentially the same action as for medium risk cases but with recommendations for insulation, heating and even double glazing (provided trickle ventilators are part of the unit) as well as minor works such as fitting door closers to kitchen and bathroom doors to prevent moist air migrating into other parts of the property.

It is also important to offer guidance to any occupier in order for them to minimise the risk of condensation by taking sensible precautions such as the venting of tumble driers to the outside and maintaining some low background heating.

Who can help?

Condensation can be totally eliminated by the installation or a Nuaire Flatmaster or Nuaire Drimaster installed by one of our highly qualified and trained installers.

You can simply purchase the unit on a supply and fit basis on this website.