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Condensation dampness 

The most common form of unwanted dampness in buildings is water from the air that forms as condensation.

How dampness from condensation occurs

The air in buildings can have a high level of relative humidity due to the activity of the occupants (e.g. cooking, drying clothes, breathing etc.). When this water laden air comes into contact with cold surfaces such as windows and cold walls it can condense, causing water to be deposited. The point at which the water held in the air changes from vapour to liquid is known as the dew point.

Condensation is often associated with poor heating and ventilation in buildings. It is more apparent in winter, as the external air temperature is low and external walls and windows are cold.

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A typical sequence of events regarding condensation

  1. Cold air enters the building
  2. The air is warmed for the comfort of the occupants
  3. The warm air takes up moisture
  4. The warm, moist air comes into contact with cold surfaces, walls, windows, etc. and is cooled below its Dew Point
  5. Condensation occurs as the excess moisture is released

Condensation dampness - within bathroom - Property Care Association

Where professionals may typically find condensation issues

Running water on windows and walls is perhaps the most immediate indication of a condensation problem. Walls in kitchens and bathrooms (where atmospheric moisture levels are usually highest), solid external walls, un-insulated solid floors and cold bridges such as concrete lintels set in cavity walls are commonly the areas in which condensation takes place. Condensation dampness can also occur under suspended floors greatly increasing the chances of fungal decay in floor timbers.

A much less common form of condensation occurs when the Dew Point is reached, not on the surface of a wall but within the structure of the building itself. This is known as interstitial condensation and can easily be mistaken for rising damp or penetrating damp.

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Problems caused by condensation

If ignored, condensation dampness can lead to a deterioration in the decorative condition of the property, stained curtains and decay in window frames. The appearance of moulds on the surface of wallpapers and paints in poorly ventilated areas is also associated with high humidities. 

Building regulations - what do they say regarding ventilation & condensation?

Building Regulation Approved Document F is the go to guide for the requirements regarding building ventilation and improving air quality within a building.  Click on the button down to find out more about Approved Document F, the key takeaways, and of course, to download the full version of the building regs.

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Free CPD videos regarding condensation & ventilation

Overcoming dampness from Condensation

+ Investigating the problem:

Condensation is a real problem and where it persists, a specialist surveyor should be engaged to explore the cause of the problem and provide advice or propose solutions. We have listed just a few of the possible methods of controlling the problem below.

Simply heating the air is unlikely to be a satisfactory solution, not only on grounds of cost, but also of practicality. Unless cold surfaces are eliminated and there is sufficient background ventilation, condensation is almost inevitable. Any remedial action, therefore, must involve lowering of moisture levels, ensuring sufficient ventilation and the elimination of cold surfaces.

Improved heating and ventilation coupled with specific action in relation to cold spots will usually result in a significant improvement in conditions, although there may be circumstances in which alternative methods are required. A modest but constant background heat is preferable to intermittent heating since this will help to maintain a higher ambient temperature in the fabric of the building.

+ Common Mechanical ventilation Strategies:

The installation of suitable extractor fans in the moisture producing rooms of a property such as the kitchen, bathroom and en-suites, will help remove the majority of this moisture-laden air from these areas (that are most responsible for condensation), with minimal running costs. This is a requirement within the Building Regulations for new properties being built, whilst also applying to existing buildings.

There are many different types of extractor fans available such as those that run continuously in the background or those which incorporate a humidistat which will control the operation of the fan within certain humidity limits. It is also possible to install fans that have an integrated heat exchanger and these have the advantage of providing effective ventilation while reducing heat loss from the property. It is very important that these types of fans are professionally specified and commissioned by a suitably trained and qualified specialist.

Where an open fire or fixed gas fire exists, a certain amount of background ventilation will occur and where additional ventilation is provided it is important that this is not blocked off.

The use of specialist insulation materials fixed to the outside of the building and insulation in cavity walls will help to improve the thermal dynamics of the building and may help overcome condensation.

+ Alternative Strategies:

An alternative to heating and ventilation for the control of moisture in the air is a dehumidifier. This is a device which draws in air, cools it to remove moisture which is collected in a reservoir and reheats it to an acceptable temperature before re-circulating it – these can be costly to run however, and may not be considered a long-term solution.

Other devices that may be considered are positive pressure condensation control units also known as Positive Input Ventilation (PIV) units. These take dryer air from roof spaces or lofts and mix this with air in the dwelling. This is done at a very low rate (below half an air change per hour) and has the effect of lowering total moisture content and removing moist air by natural leakage.

Surveying & Investigating building ventilation issues

For professionals wanting to learn more and understand the core considerations when surveying & accessing ventilation, condensation and poor air quality issues within a building, visit our page about surveying & investigating building ventilation issues by clicking the button below:

Building Ventilation - Surveying & Investigating Issues >>

Surveying  investigating condensation dampness - PCA

Our professional residential ventilation group

At the PCA, we believe the frequency of problems associated with condensation dampness leading to poor indoor air quality is getting worse.  It is partly for this reason the PCA has brought together a professional residential ventilation working group made up of many specialists that deal with condensation and poor air quality on a day to day basis.

To find out more about the Residential Ventilation Group and how you can get involved, click on the button below:

Residential Ventilation Group >>

Some training courses that might be of interest...

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Want to learn more about treating condensation & excess moisture issues

For those interested in learning more about the remediating condensation, mould and excess moisture issues within properties, there is a variety of PCA training options for surveying professionals as well as technical/trade professionals. 

Use the search tool below to find available condensation, dampness and ventilation related training courses or simply go to our training & qualifications section.  Alternatively, if you want to chat to someone, contract our training team on 01480 400 000 or contact them online.

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Ventilation in Buildings & Homes

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Ventilation Building Regulations

For a detailed insight into the regulations on ventilating buildings, click below:

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