Tuesday, November 6, 2012

Damp in Buildings – Part 1 – Condensation – How it Occurs



If left untreated condensation can become a significant problem so it is important that people understand how it occurs and how to deal with it.  Due to the fact that condensation produces water/moisture it can also act as a catalyst for a number of other defects that can be found in buildings

Source: Google Images
Most people will have seen damp in their homes in one form or another, and in fact damp is one of the most common problems encountered in houses.  Damp can manifest itself in a number of ways including ‘wet patches’ on surfaces, mould growth and sometimes a musty smell.  If left untreated damp can lead to deterioration of internal surfaces and finishes, provide a very unsightly appearance and in certain circumstances lead to health problems, particularly for vulnerable user groups such as the elderly, young children and those with respiratory conditions such as asthma.  There are a number of different types of damp that can occur in buildings including rising damp and penetrating damp, however for the purposes of this article I want to focus on condensation.

In order to understand how we can deal with condensation it is important to first understand how it occurs.  All air contains a certain amount of ‘invisible’ water vapour.  You may not realise it, but as human beings we are emitting water vapour constantly, you may not see it but it really is happening.  Water vapour is also emitted by the activities we undertake in the home including washing, cooking, drying clothes, using portable heaters such as calor gas etc.  Basically, there are large volumes of water vapour being emitted in your home and the amount of water vapour that is emitted is determined by the activites that we carry out and the number of people in your house at any particular time.  Condensation occurs when this water vapour comes into contact with cold surfaces and the air no longer has the capacity to hold any more water vapour.  In order to understand this we need to first understand relative humidity, which is generally a poorly understood term.
Relative humidity relates to the actual water vapour present in air to that which could be present and is routinely expressed as a percentage. The reason we refer to ‘relative’ humidity is because air has a varying ability to hold moisture vapour depending on temperature.  Warm air can hold more water vapour than cold air.  Once relative humidity reaches 100% it no longer has the ability to hold any more water vapour and it will start to condense on cooler surfaces (something referred to as ‘Dew Point’), which is the physical change into a liquid (condensation).
As an example, think about your bathroom.  When you have a bath or shower large quantities of water vapour are produced.  Sometimes this will develop into a ‘mist’ in the room until you open the window or turn on an extractor fan.  Have you ever noticed that you get water developing on your windows and walls?  This is condensation.  Have you ever wondered why this happens more readily on cold days, and in the warmer months it is hardly noticeable?  This is because the air in your bathroom on colder days has less capacity to hold moisture than the air in your bathroom during warmer temperatures (remember warm air can hold more water vapour than cold air).  Windows, particularly in older buildings are generally less thermally efficient than the surrounding structure such as the walls.  Therefore the internal surface temperature of the windows will be a few degrees cooler than the surface temperature of the walls.  This will mean that once dew point occurs (100% relative humidity), it will start to condense on the cooler surfaces first, i.e the windows, before it starts to condense on the surrounding walls.
Source: Google Images
Condensation can occur in any room in a house or within the structure of a house (interstitial condensation), including roof and floor voids, basically anywhere, where there is water vapour and cold surfaces.  If left untreated condensation can become a significant problem so it is important that people understand how it occurs and how to deal with it.  Due to the fact that condensation produces water/moisture it can also act as a catalyst for a number of other defects that can be found in buildings, namely timber decay such as wet rot or dry rot, as well as causing mould growth and potential health problems. 
You do not need to be a damp specialist or building surveyor to be able to deal with condensation or at least reduce the risk of it occurring.  There are numerous products on the market that claim to reduce or remove the risk of condensation in homes including paints and sprays.  These types of products may temporarily remove condensation mould that may have already occurred, or cover over damp mould, however the only certain way of reducing the risk of condensation is to understand the root cause, which will vary from building to building, and to deal with these root causes.  The usual factors that result in condensation are poor thermal insulation, inadequate heating and inadequate ventilation, or a combination of these.  In the next article I will explain how you can reduce the possibility of condensation in your home and if you already have problems with condensation I will tell you how to deal with it.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

12 comments:

  1. As you point out, a combination of poor insulation and inadequate heating can play a large part in condensation becoming prevalent in a home. Getting good insulation is a good way to help retain heat in the property and keep the temperature stable enough to reduce the amount of cold surfaces that warm air can hit.

    Good article!

    ReplyDelete
    Replies
    1. Gary has given you some solid background theory but bear in mind that relative humidity does not have to be a 100% to have condensation damp problems though it almost certainly will occur at 100% RH. It can equally occur at any relative humidity so long as surface temperatures are below dew point temperature. When it comes to diagnosis dew point temperature tells us a lot more than relative humidity.

      Delete
    2. But when vapour drops water as condensation it has to be saturated ie. at 100% humidity. Its the temperate decrease that rises the RH of the vapour to 100% when it hits a cold surface. As gary has correctly explained.

      Delete
  2. Hi gary,

    A nice article and good to see knowledge being shared in this way. Dampness of all kinds is quite straightforward once the funden=mentals are understood - well done.

    Bryan Hindle

    www.preservationexpert.co.uk

    ReplyDelete
  3. Any thoughts on Damp/condensation as an issue from Cavity Wall Insulation ? Been lucky enough to see this Industry from both sides of the fence, having spent some time Installing !! Back in the Preservation Industry now, having had a sabbatical for a number of years. Been seeing a lot of Issues related to insulation installs lately, obviously I'm aware of bad installs etc ! Sadly, it seems that the Insulation Industry has been blighted by the same problems faced by the Preservation Industry, under trained technicians and "surveyors" and bad surveys. now the Green Deal looks like going under before it has even got started !! Worrying times for those whose properties are being installed wrongly surely ??

    ReplyDelete
  4. Ross, can you share your experiences of defective cavity wall insulation please.

    Thanks
    Rob

    ReplyDelete
  5. Ross

    Many factors apply here each measure or change to the original build fabric can increase the RH with out consideration to ventilation. This is a common problem with LAs as the stock is up graded with little attention to the fact that the subject is being made air tight to a degree.

    ReplyDelete
  6. Cavity wall insulation damp is pretty awful from what I've seen and it really begs the question to me of is it worth it? The pictures in this blog look shockingly bad, no one should experience such an occurrence.

    ReplyDelete
  7. As well as building defects, it's worth touching on the health problems that can arise especially respiratory issues!

    ReplyDelete
  8. I am curious if any of this can be detected by thermal imaging?

    ReplyDelete
  9. Very good article, I'm looking forward to reading the next one!

    ReplyDelete
  10. Study the psychrometric curve; take a sling psychrometer reading or an electronic wet bulb/dry bulb temperature reading, that will give the total water content of the air, read that back to the curve line and you get the dew point. At some point in the structure the temperature gradient will be at or below dew-point and condensation will occur. A thermal imaging camera will show you the cold spots where cold bridges are and these are often the places where condensation begins. Where moist air can get into porous materials then it will migrate to the cold spots, hence the use of vapour-barriers such as foil-backed plasterboard.

    ReplyDelete