Damp Proofing London South

Damp Proofing London South Solutions for Condensation

Dampness in buildings is a serious problem. Water can enter buildings in a number of ways to cause superficial and structural damage. Conditions in a damp property are often unpleasant, uncomfortable and unhealthy.

One of the most common causes of dampness in buildings is condensation which can often lead to the appearance of mould growth. It is the presence of water condensed on walls, ceilings and other cold surfaces which support mould growth.

Throughout the UK the living conditions of a large majority of the population have been adversely affected by condensation. Its occurrence together with the subsequent mould growth has been the largest single complaint received by local authorities during the past twenty years.

In industrial premises the effects of condensation and mould growth are also well-known and have created their own particular problem especially in breweries and food processing factories.

The Problem

The problem of condensation, particularly in dwelling houses, is very much a problem of today and results from a series of relatively simple, totally invariable conditions, and is directly related to standards and methods of heating, ventilating and insulating buildings.

Air normally contains water vapour in varying quantities and its capacity to do so is related to temperature - warm air holding more water than cold air. Air is saturated when it cannot contain any more water vapour at the existing temperature; under these conditions it is said to have a relative humidity (RH) of 100%. If the temperature of the air falls until saturation point occurs the air is at a critical temperature at which it cannot hold any more water - this temperature is known as the dew point. Any further fall in temperature will result in water vapour being forced to condense out as liquid water. The amount of water vapour condensing out will be the equivalent to the amount of vapour excess of 100% RH of the air at its new temperature. Therefore, when warm air comes into contact with either colder air or a cold surface the warm air is cooled, i.e. depressing the temperature of the air to a level at which it can no longer contain all the water vapour and some of it is discarded as condensation or liquid water.

Condensation in a building usually occurs when warm air comes into contact with a cold surface. The air is cooled below its saturation point causing its excess water vapour to change into liquid water. The condensed water usually appears as water droplets or water film on non-absorbent surfaces such as windows or tiles. This form of condensation is SURFACE CONDENSATION. It is obvious and always occurs on the surfaces which are at or below the dew point of the air immediately adjacent.

Condensation can also occur within the fabric of the building due to the internal air permeating through the structure because of its greater pressure. Water vapour in the air exerts a pressure which contributes to the total pressure of the air.

The more moisture present in the air the greater the contribution of water vapour to the total pressure of the air referred to as vapour pressure. Air inside a heated building usually contains more moisture than does the external air.

This means it is at a higher pressure which tends to force the warm air through the structure taking the moisture with it. Most building materials, except metals, plastics and certain lined elements, are to some extent permeable and do not obstruct the movement of moist air through the structure. The warm moist air will eventually cool below its dew point within the fabric of the building resulting in condensation. This form of condensation is INTERSTITIAL CONDENSATION.

Interstitial Condensation is rather more complex than the surface condensation and presents a greater hazard because the resulting high moisture content can often go undetected for long periods until serious structural damage has developed such as timber decay. It will also render ineffective any insulation within the component where it occurs.

Conditions for Condensation

Condensation in dwelling houses is mainly a winter problem particularly where warm moist air is generated in living areas and then penetrated to colder parts of the building.

Water vapour is produced in relatively large quantities from a number of activities. It can also rise from damp ground under buildings and in some cases penetrate timber floors and pass freely up the cavities of brick walls into roof space. The severity and effects of condensation will then depend on the type and nature of building construction and the extent of the vapour barriers created in each design.

In timber frame buildings and wall the external cladding is liable to become wet by interstitial condensation as water vapour passes through the structure. This has caused failure of the applied painted coatings in a number of ways (loss of adhesion, blistering and chemical change) with consequent disfigurement. The use of impermeable roofing felt to prevent water vapour reaching the cladding has redirected the condensation process as moisture will condense on the sarking and drain into the framing timbers.

The traditional design of roofs has induced the occurrence of condensation, especially in the winter. In a flat or decked roof construction the waterproof roof membrane is also a vapour barrier. The water vapour is then prevented from permeating to the external environment. Condensation is then induced to occur within the roof deck or condense under the roof sheeting and drip from it.

Condensation will also occur in low pitched roof constructions particularly when the ceiling follows the slope of the roof. The wetting of ceilings with condensation will also occur when the cold air through either convection process or percolating from the external atmosphere lowers the temperature of ceilings and condenses water vapour from the underlying rooms. The effects are made apparent when little or no provision is made for ventilation of the roof space.

Condensation will often occur in brick cavity walls where moist air in the construction and external cold air circulate in a confined space. The temperature of the moist air is lowered, reaching the dew point and moisture is deposited on the coldest nearby surface, in some cases causing water to drip from the surfaces.

Condensation will also occur under suspended floors where the temperature of humid air in the floor space is lowered by cold air moving in through ventilators and water is then condensed on the underside of floor. This will often induce timber decay of the wooden floor.

The Causes of Condensation

In dwelling houses condensation is related to modern living standards, economic pressure and change in building design.

1. The main cause of condensation is naturally the generation of moist warm air by domestic activities. Moist air can come from cooking, bathing, washing and drying clothes as well as paraffin heaters and flueless gas heaters - up to 17 litres of water can be produced daily in some homes . Usually in certain areas such as bathrooms and kitchens where moist, warm air can then spread to cooler parts of the house to condense on cold surfaces.

The effect of moisture generation is further aggravated by the way houses are ventilated - it is theoretically possible to avoid condensation by adequate ventilation. Up to about the late 1960's there was natural ventilation in many homes because of the lack of double glazing, poorly fitting windows and doors, open fire places. Present attitudes have eliminated natural ventilation by the use of double glazing, draught excluders, fitted carpets (preventing air movement up through suspended wooden floorboards) and the removal of open fire places with the introduction of central heating. To put it simply the greater ventilation the greater heat capacity required to replace heat loss in this way - buildings have been effectively sealed and provided better conditions for condensation to occur.

Ventilation is only effective if consistent throughout the whole inside of the house. Further problems are encouraged by poor ventilation where stagnant air pockets are created. There is a real danger of condensation occurring where air is left undisturbed behind furniture and cupboards, often recognised by the appearance of mould growth.

1. Many houses remain unoccupied and unheated throughout the greater part of the day, allowing the fabric of the building to cool down. The moisture producing activities are then concentrated into a relatively short period. This sudden increase in warm air can produce condensation as the air comes into contact with the relatively cold structure which is still warming up.

2. Economic Pressure - dramatic increases in fuel prices force many occupiers to under use heating systems, not heat unused rooms and seal all draughts and reduce ventilation as described previously.

Background heating is often provided by flueless gas and paraffin heaters as a way of trying to heat and save costs. Excessive quantities of moisture are produced from such heaters. For every litre of paraffin burnt over one litre of moisture vaporises into air.

3. Due to changes in building design - many dwelling houses now have central heating systems where open fire places have been removed, thus reducing natural ventilation.

Windows without controllable ventilation became popular and permanent ventilators were not used in rooms without a flue.

Modern changes in roof design, including elimination or overhanging eaves and lowering the pitch, also reduced ventilation and increased the likelihood of condensation.

Any condensation problems call Damp Proofing London South on 0207 498 2837 or 07912 306337.