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.
Condensation can be controlled by filling a loft unit. These cost £680.00 + VAT
