10/12/2015
GUIDE TO CONDENSATION
WELL WORTH TO READ IF U HAVE THIS ISSUE
Air always contains some invisible water vapour. The amount of water vapour that the air can hold depends on its temperature - warm air can hold more water vapour than cold air. When warm moist (humid) air comes into contact with a cold surface, it will cool and may become saturated. If it cools further, some of the water vapour will condense out on the cold surface.
The people living in a house add to the water vapour in the air simply by breathing (picture your breath on a cold morning) and through activities such as cooking and bathing. Normally, this moist air leaves the house through ventilation.
Ventilation not only removes moisture, but also provides fresh air for occupants to breathe, and removes pollutants and odours. However, if moisture is allowed to accumulate in the house, some of it may condense on cold surfaces within the building, particularly in winter. Examples of such cold surfaces include:-
Single glazed windows
Cold water pipes
Uninsulated external walls and ceilings, particularly at corners and at the north side of the house
External walls behind large items of furniture and within built-in wardrobes
Around the edges of window and door openings, where surface temperatures may be lower due to an uninsulated part of an otherwise insulated wall (a ‘thermal bridge’).
In many houses, the inside surfaces of single-glazed windows often become damp due to condensation. This is particularly noticeable in the mornings in unheated rooms in an otherwise well-heated house. However, the same process can take place on any relatively cold surface such as an outside wall. Provided the amounts of moisture are small and infrequent and that they ev***rate fairly quickly, this will not usually harm the building. However, if dampness due to condensation persists for lengthy periods, it can damage the building’s structure and interior decor. Signs of condensation problems include the following:-
Frequent condensation on windows in winter, with pools of water collecting on window-boards
Mould growth on walls, ceilings or cupboard spaces located on outside walls
A musty, damp smell, even though there may be no visible signs of dampness.
TYPES OF CONDENSATION
Surface condensation
The type of condensation where moisture appears on visible surfaces within the building is called surface condensation. It may be seen to occur at times when large amounts of moisture are being produced in the house or room, especially during cold weather when windows and vents are closed.
Interstitial condensation
This is condensation that occurs within external walls, floors and roofs. It occurs when warm moist air from inside the house passes through gaps in the internal surface and condenses at colder parts within. Since it cannot be seen, it is more difficult to identify. It may give rise to a damp, musty smell, and possibly mould growth on the inside surface.
However, other causes of dampness can produce similar effects. Internally insulated walls with a deficient or damaged vapour barrier are particularly vulnerable to interstitial condensation.
EFFECTS OF CONDENSATION
Persistent dampness due to condensation can have the following effects:
DECAY
Wood and other building materials may decay, giving rise to structural and other damage.
MOULD
Mould grows in damp, humid, warm conditions. If a wall or ceiling is frequently damp with condensation, mould may form on it. Mould usually appears initially as spots or small patches, usually grey-green, brown or black in colour, which grow in size and number with time.
HEAT LOSS
The effectiveness of some insulation materials will be seriously reduced by dampness. If insulation becomes damp, either through condensation or by other means, heat loss from the house will increase. In addition, the insulation and the room surface inside it will then be colder, increasing the likelihood of further condensation.
SOURCES OF MOISTURE
A typical four-person household (two adults and two children) may produce in the region of 5 to 12 kilograms of water vapour per day. The main sources include breathing (exhaled air contains more moisture than inhaled air), cooking,bathing, clothes drying and the use of free-standing (i.e. flueless) gas and paraffin heaters.
CONTROLLING SURFACE CONDENSATION
To reduce condensation, do one or both of the following:
Reduce the amount of water vapour in internal air, by removing moisture at source and/or increasing overall ventilation rates.
Increase internal temperatures, by insulation and/or additional heating.
Remove moisture at source
When cooking, particularly when generating lots of steam, open windows and vents in the kitchen to let out the steam and close the kitchen’s internal door to prevent the steam from entering the rest of the house. If there are vents or open windows in two walls, this will help to provide ventilation across the room even on days with only a slight breeze.
An extractor fan or cooker hood will help to remove steam and moist air. Since such fans extract heat as well as moisture, closing the kitchen’s internal door will prevent heat from being extracted from the rest of the house. Air extracted must be replaced by air intake somewhere else, so another vent in the kitchen may need to be opened to allow replacement air to be drawn in.
When bathing, close the door and open the fly window a little while bathing or more immediately afterwards. In internal bathrooms mechanical or stack ventilation is required. This should be controlled so that it is not left switched on for any longer than required, since it extracts heat as well as moisture. Dry clothes outdoors whenever possible. If hanging clothes up to dry in a utility room, close the internal door and open a window or vent slightly (not too much, otherwise the room will cool down, reducing the drying rate). Always vent tumble dryers to the outside.
Free-standing heaters (i.e. those with no flue to the outside) burning fuels such as gas or paraffin release water vapour into the room as they operate. Burning one litre of paraffin will produce about one kilogram of water vapour. In rooms with such heaters, adequate ventilation is always required not only to remove water vapour and other combustion products (fumes) from the room, but also to supply combustion air to the heater. In buildings vulnerable to condensation, a heater with a flue to carry fumes to the outside is preferable.
ENSURE ADEQUATE VENTILATION
The ventilation rate should be high enough to prevent the build-up of moisture (and pollutants) in the indoor air, but should not be so high that it causes excessive heat loss.
The optimum ventilation rate will vary depending on what activity is going on and the weather conditions on the day. In well-sealed houses (e.g. those with draughtstripped doors and windows, blocked-off chimneys, etc.), ventilation should be provided through controllable openings such as trickle vents or windows that can be secured in a marginally open position. These can be adjusted by occupants in response to ventilation requirements. For example, they might be opened on calm days when large amounts of moisture are being generated in the house, and closed on windy days when little moisture is being produced. Signs such as misting up of windows indicate the need for increased ventilation.
INSULATION
Insulation of the building will raise internal surface temperatures, reducing the likelihood of surface condensation. Also, whatever condensation does occur will ev***rate more quickly. Similarly, the use of double glazing or, better still, low-emissivity double glazing, rather than single glazing, will reduce the likelihood of condensation on windows. If aluminium window-frames are to be installed, these should have a ‘thermal break’, otherwise condensation may occur on the frame itself.
HEATING
Additional heating will have a similar effect to insulation – it will raise internal temperatures and reduce the incidence of condensation. Ventilation will still be needed to prevent the accumulation of moisture.
CONTROLLING INTERSTITIAL CONDENSATION
If interstitial condensation is suspected, check for any gaps or holes in the surfaces of external walls, the ground floor and the top-floor ceiling, and seal these to prevent moist air from getting inside. The methods for reducing surface condensation described above will also help. If the problem persists, seek professional advice.
CONDENSATION IN THE ATTIC
If there are gaps in the ceiling of the top floor, warm humid air from the house may pass through the ceiling into the attic, where it may condense on cold surfaces. This may cause rotting of timber or, if it drips down onto insulation, reduced effectiveness of insulation and increased heat loss.
To avoid attic condensation problems:
(a) Ensure that there is adequate ventilation in the attic. In conventional pitched roofs (unconverted), there should be a gap at the eaves on opposite sides of the roof to allow cross-ventilation above the insulation. It is recommended that the area of these gaps should be equivalent to a continuous opening of not less than 10 mm (about a halfinch).
(b) Seal any gaps in the ceiling below the attic.The attic hatch should be draught-sealed (light-weight hatches may need to be clamped or weighted to ensure adequate pressure against the seal). Gaps around pipes or light fittings penetrating the ceiling and cracks at wall-heads should be sealed.
(c) Ensure that the water tank and pipes in the attic are insulated to avoid condensation on them.
FURTHER TIPS
When cooking by boiling, keeping lids on pots will reduce steam generation as well as saving energy.
Do not allow water that has condensed on cold water pipes to run down to where it may cause damage or present a safety hazard.
If condensation occurs within cupboards mounted on external walls, leave the cupboard doors open to ventilate the affected surfaces. Insulate the wall at the back of the cupboard to prevent recurrence.
Some new buildings can take time to dry out. Extra heat and ventilation may be needed to ev***rate moisture during the first winter after construction and care may be needed in mopping up condensation.
Other causes of dampness
Apart from condensation, other possible causes of dampness in buildings include
Rain pe*******on through walls, roofs or around window and door openings.
Rising damp, i.e. moisture from the ground rising up within a wall or floor.
A leaking pipe, tank or gutter.
Drying out of a newly-constructed house or a house that has recently been flooded.
If the dampness problem is not solved by the measures described in this article, it may be due to a cause other than condensation, and professional advice should be sought on how to deal with it.
