The frequency that condensation is being identified as problematic in buildings has significantly increased in recent years.
There are 5 major factors that need investigation to assess the effective control of condensation and resulting mould growth.
- Ventilation: Is it adequate for the occupancy/volume of the property.
- Heating: Again is it adequate for the occupancy/volume of the property.
- Moisture production within property: is it reasonable, given the variation in life styles, number of occupants, cooking and drying of clothes and pets etc.
- Air Flow: Lack of air movement behind furniture in particular, such as wardrobes and wall cupboards
- Insulation: are there any causes of thermal bridging (cold spots).
Ideally in domestic dwellings the relative humidity during winter should be kept below an average of 60%.
As the air cools when it come into contact with a cold surface the capacity of the air to retain water declines,( and therefore the relative humidity increases)until at a specific temperature, depending on condition’s ,it cannot retain the excess of water now present; the excess water now drops out of the air as condensation onto the cold surface.
It is important to understand that the excess water vapour in the internal environment responsible to surface condensation is not derived from damp walls or floors.
The excess internal water vapour is the result of occupation (‘lifestyle’) as a result of washing, cooking, bathing, and people breathing, etc. As a result the excess water vapour is generated constantly with the property as a ‘normal part of occupation up to approximately 15 litres (nearly 4 gallons being produced by an average occupying family.
Wet/damp walls are not therefore required for surface condensation to occur, and it occurs mostly on dry walls and ceilings and as such it is very much restricted to the surface, frequently not penetrating more than a couple of millimetres on permeable surfaces and on paint films and vinyl paper and other less permeable finishes it will remain distinctly on the surface.
It does not lead to dampness through the whole thickness of the wall like rising damp.
A low relative humidity is very important for evaporation with higher relative humidity reducing this process leading to sub-optimal conditions especially during the colder months of the year.
Given that a property can have can have four external elevations, only two are likely to be exposed to the wind at any one time and two will probably be sheltered.
Indeed the wind speed around the base of most walls is almost certainly much lower than at high levels, even on windy days.
So combinations of low wind speed, low temperatures and high relative humilities, part of the building in shelter and the wind striking the wall at a non-optimal angle would without doubt, subject the system to long term sub-optimal conditions during which time constant and continuous sources of water ingress must simply pass by the units as under such conditions they are incapable of operating effectively.
Environmental Protection Act 1990 Chapter 43, Section 82. States it is a landlords legal responsibility to deal with dampness problems as well as it being a duty of care. The main problem is condensation, which is nearly always seen as mould growth.
Under the law this can be deemed as a statutory nuisance. An action can be brought under the Act, which is of a criminal nature and can attract significant fines.
There are reasons to believe that the growth of fungi and mould in the built environment may affect human health, depending on the extent of the growth, the length of exposure and the general health of the occupants.
Possible reasons for becoming a more widespread issue:
- Changes in construction methods
- Introduction of vapour barriers
- Fitting of draught proofers
- Construction of air tight buildings
- High density insulation
Methods of controlling condensation
- Improved Ventilation-sweeps out moisture laden air and replaces with drier air from outside.
- Increase temperature- constant heat rather than intermittent-raise temperature sufficient to bring environment out of the ‘mould risk’ area. This will increase wall/surface temperature thereby lowering the risk of condensation/mould growth.
- Reduce sources of moisture-ie limit use of electrical clothes dryers portable gas or paraffin heaters.
- Improve thermal properties of walls by keeping dry (where possible)
- Provide dehumidifiers
- Improve surface temperatures reduce thermal bridging (cold spots).