Your Questions Answered Condensation
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WHAT IS INTERSTITIAL CONDENSATION? (CONDENSATION)
My contractor says I have interstitial condensation. What is this? Question:
WHAT IS INTERSTITIAL CONDENSATION? (CONDENSATION)
My contractor says I have interstitial condensation. What is this? Submitted by: Rob Jones
Answer:
Most of us are familiar with visible surface condensation that forms on the inside of windows and wall surfaces during cooler weather. This happens because the glass or wall surface is at or below the ‘dew point temperature’, (the temperature at which water reverts from its gas state to a liquid) relevant to the environment in which they are present. Interstitial condensation is still the process of water reverting from its gas state to its liquid state, but the difference is that the point at which this occurs is within the thickness of a wall or ceiling (rather than on the surface).
Most walls in residential properties are porous and allow water vapour to pass through them. This is one of the main ‘escape routes’ of water vapour from the inside of a property to the outside. In a solid wall there will be a declining temperature gradient between the usually warmer inner wall surface and the exterior. Interstitial condensation will form when the dew point temperature is within the thickness of the wall or ceiling and the water vapour passing through the wall reaches that point.
If the resistance to the passage of water vapour and heat conducting properties of the building materials used in your property are known, then it is possible to calculate at what point interstitial condensation will occur within say a wall. It should be appreciated that this is a risk calculation only that uses prescribed internal and external conditions and the whole procedure is outlined on BS 5250; 2002. Has your contractor made these calculations to arrive at his conclusion?
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HEAT RECOVERY FAN (CONDENSATION)
I had replastering works done about 4 months ago. I then tried to have my decorator paint the area but she refused saying that it is still damp. Is this normal? I have one quote from a damp proof agency that states that we also need a heat recovery fan to stop condensation. Do you have any comments on the heat recovery fan? Question:
HEAT RECOVERY FAN (CONDENSATION)
I had replastering works done about 4 months ago. I then tried to have my decorator paint the area but she refused saying that it is still damp. Is this normal? I have one quote from a damp proof agency that states that we also need a heat recovery fan to stop condensation. Do you have any comments on the heat recovery fan? Submitted by: Ann Robinson
Answer:
It is difficult to answer your question without knowing more specific details. You do not state where in the property or the reason why replastering was undertaken. If the new plaster was applied onto a dry surface then one would expect it to have dried after 4 months. If it was because the area was damp then what caused the damp and has its source been eliminated? Your decorator is correct not to cover a damp surface as to do so would be a waste of time and money.
You also state that a damp proof company has recommended a heat recovery fan to stop condensation. Has active condensation been diagnosed in your property? At various times of the day has someone taken relative humidity readings, the air temperature, established the dew point temperature and taken wall surface temperature readings to see if they are above or below the dew point temperature? Have any other condensation monitoring procedures been used? Do you suspect condensation is a problem?
Condensation is a consequence of life style i.e. how you live in your house and your water vapour generating activities such as internal clothes drying, cooking without extraction etc. Some properties are more susceptible to the effects of condensation than others. A heat recovery fan, if installed correctly, may contribute towards the control of a condensation problem. How effective it will be is dependant upon the severity of the problem. It may be sufficient on its own but it is possible that other control measures may also be necessary or perhaps, subject to the circumstances, be even more effective than a heat recovery extractor.
If you would like to supply more details about your problem(s) we should be able to provide you with a more informative answer.
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RUSTY WET NAIL AND MOULD? (CONDENSATION)
In the 2nd bedroom of my bungalow there was black mould on the wallpaper and a rusty wet nail in the skirting board on the outside wall. On removing the paper the plaster was dry with no sign of damp or mould. Could you suggest what has happened to the skirting board please? Question:
RUSTY WET NAIL AND MOULD? (CONDENSATION)
In the 2nd bedroom of my bungalow there was black mould on the wallpaper and a rusty wet nail in the skirting board on the outside wall. On removing the paper the plaster was dry with no sign of damp or mould. Could you suggest what has happened to the skirting board please? Submitted by: Mike Green
Answer:
Of course you should check outside first for any potential causes of damp penetration. From what you describe however it sounds very much like condensation is the cause of your problem. Mould will normally only grow on a wall where there is a pure water source such as rain water, tap water or condensation. It will not grow on surfaces where the water has originated from the ground - such as rising damp as this contains salts and minerals which act as a 'mouldicide'.
Bungalows are notorious for suffering the effects of condensation. Spare bedrooms can suffer badly – especially north walls. Condensation is caused by lifestyle – i.e. what you do in your house - and probably the single biggest contributor is drying clothes internally on and against radiators. This bad practice will affect all rooms even if you do not dry the clothes in the room in question. The condensation season is November to March and very probably during the summer you will not experience a problem. The rusty nail head is likely to be due to condensation forming on it since the nail head will be colder than the surrounding wood.
Look at everything that you do that produces water vapour - cooking, washing, clothes drying etc. and extract as much water vapour as possible directly to the outside at source. Insulate the property well especially cavity walls. If you insulate the walls the inner skin of brickwork will be warmer and therefore less prone to the effects of condensation.
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CONDENSATION ON DOOR FRAME (CONDENSATION)
I just installed a new garden door in my house, where the old sliding door was. In the basement I have a gas stove that I use to heat the basement. Now the problem is that when the gas stove is on then I get a lot of condensation on the metal frame of the door and it is getting on the living room floor.
Question:
CONDENSATION ON DOOR FRAME (CONDENSATION)
I just installed a new garden door in my house, where the old sliding door was. In the basement I have a gas stove that I use to heat the basement. Now the problem is that when the gas stove is on then I get a lot of condensation on the metal frame of the door and it is getting on the living room floor.
Submitted by: Victor Turpin
Answer:
You do not state the type of gas stove you have but if you have a portable calor gas type of heater then we are not surprised that you are getting condensation as this type of heater produces vast quantities of water vapour as a product of combustion. All gas combustion produces water vapour and other bad gasses so you need to make certain that the area in question is adequately ventilated when the heater is on and we would recommend that you install a Carbon Monoxide detector - it could save your life. Metal door and window frames always tend to suffer from condensation even if no where else does since they conduct heat/cold very well. Some actually have a thermal break in built to help reduce this.
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CONDENSATION ON WINDOWS AT 45% RH? (CONDENSATION)
In our house we have new, very tight double glazed windows. The HVAC system is hot air with adjustable humidification. When I raised the humidification to 45% (because our plants were suffering from dryness), the condensation on the windows produced significant pooling of water at the bottom of the glass. Is there anything to do?
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CONDENSATION ON WINDOWS AT 45% RH? (CONDENSATION)
In our house we have new, very tight double glazed windows. The HVAC system is hot air with adjustable humidification. When I raised the humidification to 45% (because our plants were suffering from dryness), the condensation on the windows produced significant pooling of water at the bottom of the glass. Is there anything to do?
Submitted by: Franz Allina
Answer:
Do not be totally hung up on the relative humidity reading alone.The varying temperature within the property will change the relative humidity without adding or taking away any moisture. Relative humidity will increase if temperature falls and could therefore give rise to your situation. We suggest that you check the humidification regulator is functioning correctly and is correctly calibrated. You do not state if it is condensation forming on the glass or the frame or both. If your double glazing is new does it not have trickle ventilators built in? If not then try cracking the window open just a little to enable some ventilation. Also make certain you do everything possible to remove excess water vapour generated at source i.e. powered extraction in the bathroom and above the cooker and NO clothes drying inside - EVER! Remember it is what you do in your home that produces the water vapour that eventually forms as condensation.
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DAMP PARENT'S BUNGALOW (CONDENSATION)
I really hope that you have some advice regarding damp in my parent’s bungalow. My parents are quite elderly; their bungalow was built in the 1960s and has always suffered from damp and a form of grey mould mainly in the corners on the external walls. Is this rising damp and could this be from a damp course that has now stopped working? They have tried everything from cavity wall insulation, special paint and lining the walls with polystyrene sheets but it is still present. Should they have a new damp course fitted or will this not make any difference? Question:
DAMP PARENT'S BUNGALOW (CONDENSATION)
I really hope that you have some advice regarding damp in my parent’s bungalow. My parents are quite elderly; their bungalow was built in the 1960s and has always suffered from damp and a form of grey mould mainly in the corners on the external walls. Is this rising damp and could this be from a damp course that has now stopped working? They have tried everything from cavity wall insulation, special paint and lining the walls with polystyrene sheets but it is still present. Should they have a new damp course fitted or will this not make any difference? Submitted by: Sam Cheesman
Answer:
It is very unlikely that the damp proof course has failed. Bungalows tend to be more susceptible to condensation during the cooler winter months and effective insulation combined with an adequate consistent dry form of heat is essential to reduce the likelihood of condensation forming. It cost a great deal of money to provide adequate heat throughout a property and very often the bedrooms suffer the worse effects of condensation as they tend not to be heated to the same extent as other areas. Elderly people on fixed limited income tend to heat the living room but the other areas are sporadically heated which might warm the air for a short time but not the fabric of the property. Naturally lifestyle of the occupants should be looked at and all water vapour generating activities such as clothes drying, cooking, washing etc. should be assessed to see if the water vapour may be extracted at source or stopped. It is appreciated that we all have to live and you may wish to consider installing a domestic dehumidifier to run during the winter months.
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NEW BUILD MOULD PROBLEM (CONDENSATION)
We moved into a new property in December 06 - by Christmas we noticed the inside wall of our utility room (behind where the washing machine would sit and not on an outside wall) is beginning to peel and black mould is forming. The developer has been back in to assess the problem (as it seems to be appearing in two other properties that are yet to be sold) and is saying its 'rising damp'. Being naive to this problem (and not trusting the developer!) should we be seeing rising damp on such a new property that should have passed all the building regulations (i.e. suitable damp course), adequate ventilation etc? Just a co-incidence our garden (less than 3m from the house) is constantly flooded and this, according to the developer "should dry out over time" - could the two be connected?
Question:
NEW BUILD MOULD PROBLEM (CONDENSATION)
We moved into a new property in December 06 - by Christmas we noticed the inside wall of our utility room (behind where the washing machine would sit and not on an outside wall) is beginning to peel and black mould is forming. The developer has been back in to assess the problem (as it seems to be appearing in two other properties that are yet to be sold) and is saying its 'rising damp'. Being naive to this problem (and not trusting the developer!) should we be seeing rising damp on such a new property that should have passed all the building regulations (i.e. suitable damp course), adequate ventilation etc? Just a co-incidence our garden (less than 3m from the house) is constantly flooded and this, according to the developer "should dry out over time" - could the two be connected?
Submitted by: Lindsey
Answer:
We deduce from your question that the property is brand new. We are also going to deduce that there is a recess between base units where the washing machine would be positioned. Condensation and mould can sometimes be a problem in new-build properties as the thousands of gallons of water used during construction evaporate off. It is possible therefore that the washing machine recess is for some reason susceptible to the formation of condensation during this process and indeed other wall surfaces may also be affected but are concealed by kitchen base units, etc. We doubt very much indeed that rising damp is the problem. Mould will only grow where there is a pure water source, i.e., rainwater, tap water or condensation. It does not grow where the source of moisture originated from the ground, i.e., rising damp, as this contains salts, minerals and impurities that act as a mouldicide. The paint film is possibly peeling away due to the formation of sulphates beneath it which is not unusual as the construction moisture evaporates off, though we would have expected a vapour permeable paint to have been used.
With regard to your flooded garden, this would have no effect or influence on the environment within your property. We are not horticulturalists but cannot understand why a garden flooded now should dry out over time. You would have to consult with the appropriate expert about this.
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MOULD HARMFUL TO HEALTH? (CONDENSATION)
Is the black thick condensation mould harmful to my health if breathed in?
Question:
MOULD HARMFUL TO HEALTH? (CONDENSATION)
Is the black thick condensation mould harmful to my health if breathed in?
Submitted by: Gemma Midwinter
Answer:
If mould is present in sufficient quantity then the spores it will release could be hazardous to health - there would have to be a great deal of mould for this situation to arise. What is causing the mould to occur and why not remove it?
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MORE AND MORE DAMP (CONDENSATION)
My son’s house has become gradually damper over the last few years, and they now use a dehumidifier which removes litres of water a day. They have noticed that when they had the cavity wall insulation installed, which was a few years ago, 2 of the air bricks are now blocked with the foam. Is this likely to be a cause of the damp? They also had the underside of the roof sealed with solid foam - could this be in any way a factor?
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MORE AND MORE DAMP (CONDENSATION)
My son’s house has become gradually damper over the last few years, and they now use a dehumidifier which removes litres of water a day. They have noticed that when they had the cavity wall insulation installed, which was a few years ago, 2 of the air bricks are now blocked with the foam. Is this likely to be a cause of the damp? They also had the underside of the roof sealed with solid foam - could this be in any way a factor?
Submitted by: N Chapman
Answer:
The foam cavity wall insulation (are you sure it was foam?), blocked air vents and foamed roof are all likely to have reduced the vapour permeability of the building. This is the ability of the building to allow the natural movement of water vapour from an area of high vapour pressure (inside) to an area of lower vapour pressure (outside). It is possible that your son’s life style may also have changed such as additional children, dogs etc. which may be a contributory factor. Obviously the blocked air vents should be cleared out and it is also very important to extract all water vapour generated inside at source i.e. extractors in the kitchen and bathroom and NEVER dry clothes inside. Consider installing some trickle ventilators.
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IS IT CONDENSATION? (CONDENSATION)
How do I know if dampness is caused by condensation? Question:
IS IT CONDENSATION? (CONDENSATION)
How do I know if dampness is caused by condensation? Submitted by: R Clark
Answer:
Condensation tends to occur in the cooler months typically between November and March. If your area of concern is permanently damp, even during the summer months then the cause is probably not condensation
Black spot mould growth on walls and adjacent surfaces in properties is commonly associated with condensation. As a general rule mould will only grow on surfaces where there is a pure water source such as rain water, tap water or condensation. It is very unusual for it to grow on damp wall surfaces where the source of moisture originated from the ground. This is because ground water contains salts and other impurities that effectively act as a mouldicide.
If the damp appears on some days and disappears on others, it could be condensation but it could also be due to hygroscopic salt contamination as a result of rising damp or moisture ingress near or adjacent to a chimney flue.
Evidence of a consequence of condensation in the form of mould growth on wall surfaces usually shows itself first at low level in corners, on outside walls, curving upwards into the corner and tapering down towards the skirting board.
It is possible with the correct instruments to undertake a simple test to see if condensation is occurring in a room at a given time by taking air temperature and relative humidity readings. From these two figures it is possible to establish the dew point temperature (the temperature at which condensation will form in that specific atmosphere). Surface temperature readings may then be taken to see if a wall’s temperature is above or below the dew point temperature. If it is above it means no condensation is occuring, below means condensation is occurring. It should be appreciated that such a test is only a photograph in time. During the 24 hour cycle of house occupancy such readings and results will vary considerably. Longer monitoring using data loggers would be the prefered option. It is of course possible to have condensation and rising damp at the same time and it is sometimes difficult to differentiate between the two on site.
One further test that could be employed is to remove a plaster sample from the suspect damp area near to the highest damp point. This sample could then be tested for chloride and nitrate salts which are hygroscopic (moisture attracting). If such salts are present then provided the sample was not taken from near a chimney, they could only have come from the ground. This would mean that rising damp has either affected the wall at some time in the past or is still currently present. If no salts are found then it is unlikely that the damp originated from the ground and condensation or penetrating damp could be a possible cause.
If all else fails call in a qualified expert but try to make sure he is up to speed on condensation.