Managing and understanding condensation in buildings
Firstly: Condensation does not just happen on the wall.
Condensation happens INSIDE walls.
Condensation on or within walls is a common problem in old houses, and to a lesser extent in new houses, which should comply with building regulations – these are meant to avoid problems such as condensation. Condensation in old houses causes the phenomenon most commonly called 'Rising Damp'.
Temperature + Humidity = Condensation...
How does water get into a wall you ask? Simple really - the air around us has lots of water in it. It is a gas - harmless, not wet - and moves around in everything. It is passing through the walls around you now - together with oxygen and nitrogen and a bit of carbon dioxide. So your old house walls always have a bit of water in them as a vapour and it does no harm. If you cool the wall, water can turn to a liquid - condensation. The coldest bit of the wall is the bit nearest the gound, or a very exposed outer corner of an upper bedroom, or underneath a bay window. If the water which forms as condensation can evaporate - through lime plaster, or lime mortar or stone, it goes as soon as it forms really - just evaporates away like the rainwater on your paving stones dries when the rain stops. If you trap it - with gypsum plaster or cement render, or cement pointing on the outsdie of the wall - it can't get out and the wall gets wet. THAT is what the damp wallies call rising damp. Its nothing to do with rising damp - it's just condensation.
We have sophisticated, yet simple measuring equipment which allows us to monitor the levels of humidity and the temperature in your house. From these, we calculate the 'Dew Point' - the temperature at which condensation forms. It is then a simple process to check the temperature of walls and pinpoint those which are at risk, and those which actually have condensation forming on them.
A recent survey provided the best example we could ever quote. Our client asked us to survey his house and try to ascertain why mould was suddenly appearing on the walls around the house. He complained that there were damp patches all over the house, and mould growing on clothes and belongings in cupboards. Plaster was peeling in some areas, together with paint finishes. As soon as we entered the house, we took ambient humidity and temperature readings - these showed humidity of over 70% and a room temperature of 22 degrees C. The dew point, at which temperature condensation will start to form, was in this case calculated at 13.5 degrees. A spot check of the walls in the worst affected areas (using a very sensitive thermocouple) showed that they were all at or below dew point, and thus condensation was actively forming - which is why the walls were wet.. We opened a window at the front of the house by an inch, and the back door by a similar amount, which was just enough to allow a flow of air into the house. Within two hours, condensation on the walls had disappeared. Checks of the humidity and temp levels showed that the humidity had dropped to below 60%, and the temperature only by 3 degrees - the house felt warmer, and there was now a big gap between the temperature of the walls, and the dew point, which had dropped considerably. Our client was delighted, his problems were essentially solved - we recommended a series of small changes in his lifestyle, some ventilation fans, and air vents - all at minimal cost. The house is now starting to become dry and mould free. Luckily, we got to this one before the plaster dropped off and damage occurred to finishes.
In another survey, the client was using gas fires to heat the place. A huge woodburner in the middle of the house was never used. We made him cut off the gas fires and use the woodburner. A month later, he rang me to say that they did not need to do any of the re-plastering or damp works that other 'Timber and Damp Surveyors' had told him to do - and that just by turning the gas fires off and using the wood burner - "You've changed our lives - our asthma problems have stopped, the house is warmer, and dry as a bone - the mould has disappeared from our clothes''
These two photos below are probably the most significant examples of what can happen to a wall that I've ever seen. Look carefully at them, and the pattern of 'damp' that is repeating in the first picture - then have a look at the detailed explanation below the photos...
However... Look more closely. At the top of the photo, where the wallpaper starts again, you can see that the plaster itself is bubbling and soft - it's actually damaged. What has caused this damage I wonder...? For the answer, we have to look at the other side of the wall - in the photo to the right...
Every action with an old house involving anything impervious, anything that traps water and stops the building breathing, will result in an unpleasant reaction somewhere else!
I wonder why?
We tested the temperature and humidity of the walls. The wall on the right is covered with original lime plaster. The temperature probe showed a temperature of almost 2 degrees higher for the lime plaster than the wall with the mould on it - which was cement rendered and nearly 2 degrees colder.
Another example of how modern materials dont work, and traditional materials are warmer and drier.!
Thermal images of condensation in the corner of a room
These images are to show you how temperature varies in walls. This is the corner of a room - to the right of the picture is the outer wall. The wall in front of you - to the left of the pic, is also an external reveal, with another wall running off it away from you... This means that the corner is a very cold corner, exposed to wind and temperature. Rising damp ? No, of course not - but the coldest part of a wall is the bit at the bottom - the warmest - at the top. Cold corner - cold in the corner. So you get this textbook triangleof cold at the bottom of the triangle and warmer at the top, with the associated mould pattern from condensation in the cold bit.
It's all very simple really - this is what condensation is all about - and yet people insist on calling every occurrence of mould as rising damp - now you start to visualise - its not!