Richard Greenland
Landlords often blame tenants’ bad habits for condensation in rental flats, but you can make your properties much less prone to it. It’s also easy to confuse extreme condensation in poorly-insulated houses for penetrating damp. The key to stopping condensation is making all the interior surfaces warm. Ventilation is only a very secondary solution. Current Building regulations specify high standards of air-tightness for residential buildings, keeping occupants warm and saving power. Insisting that tenants open windows or use constant extractors in cold weather is unreasonable when the fault is poor insulation.
condensation at edge of poorly-insulated bathroom ceiling
Keeping inside surfaces warm is not difficult or expensive compared to the cost of extra heating, and grants are often available through the council. Ceilings should be insulated with a minimum of 270mm fibreglass to meet current standards, which should not be squashed by stored junk! Even 100mm will make a massive difference. The edges of the ceiling adjacent to outside walls get cold more easily and insulation should be pushed right into the corners, without obscuring any air-vents into the attic.
Cavity walls can be filled from the outside with little disturbance to tenants. Solid outside walls can be insulated with thin insulating ‘papers’ like Sempatap. It’s not hard to apply and only 10mm thick so doesn’t require re-fitting of skirtings, door linings etc. It can make a massive difference to the surface temperature of walls, with concomitant reductions in condensation. It still falls well short of building regs standards for renovated property, which normally requires 50mm of closed-cell phenolic foam insulation for solid walls. This is MANDATORY if you’re replacing more than 25% of plaster on any outside-facing wall. It’s particularly important to insulate around the bottoms of windows as they commonly accumulate heavy condensation.
Single-glazed windows in well-insulated homes often attract massive condensation. If double glazing is too expensive, consider secondary glazing, which often gives better insulation anyway because of the larger gap. If this is still to expensive, you can improvise with clingfilm over window casements to create a gap between the glass. You’ll also need to thoroughly seal all drafts between casements and frames with brush- or foam-type draft excluders.
Condensation mould can grow where wardrobes or pictures restrict ventilation of poorly-insulated outside walls. Moving them usually sorts the problem.
The bonus of all this condensation-prevention is it keeps your tenants warm and their heating bills down. Warm tenants with low bills are less likely to leave your flats!
So far I’ve given three causes of damp: rising, penetrating, and condensation. As a builder I’ve found people often confuse them, so I should identify some of the odd sources of damp which confuse people the most. Did you know that Jackdaws can cause damp in older houses – I’ll explain how next week.
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I’m posting this in response to posts on propertytribes still advocating ventilation. This is like closing the gate after the horse has bolted. To reiterate, ventilation is a second-line defence. Your first line should be preventing moisture getting into the house in the first pace. You do this using barrier methods as described in the earlier blogs. And by keeping all surfaces warm, which prevents undue condensation. As a rough guide, NO HOUSE SHOULD BECOME DAMP IF LEFT UNOCCUPIED. Dryness should be built-in and ventilation unnecessary.
When the house is occupied occasional ventilation will be necessary, for instance when cooking or after bathing. Constant ventilation should be unnecessary and just makes occupants cold!
I disagree with your opinion that ventilation is a secondary solution. You are advocating virtually sealing the building. If there is moisture in the building,it needs to escape. If it does not and remains trapped,it has to settle somewhere-usually along the wall bottom,which will be the coolest.Black spot mould is usually the result.
Hi Bill, this is a common misconception born from centuries of British people living in cold, dark, damp homes. Warm air in warm rooms holds far more evaporated water than cold air, and this airborne moisture esapes whenever a door is opened, letting in cooler, dryer air. Or it gradually permeates through walls and ceilings which are naturally vapour-permeable. Provided, that is, the walls and ceilings are kept warm, preventing moisture condensing on them!
I appreciate this may be hard to understand for those who have never experienced truly well-insulated buildings. I can assure you my flats were built to very high standards of insulation AND air-tightness, and the tenants have virtually no problems with condensation, except on the bathroom window. This is in spite of habitually drying clothes on radiators.
Sorry rich but you got this wrong mate.
by just insulating the walls you are not addressing the real issue, all that will do is move the problem else where and you will still have a problem with moist air.
1. condensation is not caused by outside factors such as rising damp or penetrating damp. they have very little if any effect on condensation.
2. the first thing to do when combating condensation is to cut down on moisture production, ie no drying washing on rads and clothes horses, using extractor fan when showering and cooking.
3.keep the property well heated and ventilated, this is far more important than insulation.
4. insulation is the last aspect to consider not the first.
Nick,
1. I didn’t say it was.
2. I like to dry MY clothes on rads so I don’t see why tenants shouldn’t.
3. I don’t like high heating bills and I don’t like drafts, so don’t see why my tenants should.
4. If you think that then I can only assume you have never lived in a modern well-insulated house. My tenants all dry clothes on rads/ doors/ bannistairs/ clothes rack/ anywhere they can think of. I don’t discourage this. The flats are extremely well insulated so there is virtually no condensation except on a few isolated cold spots. If tenants did this in a cold, drafty, unmodernised Victorian terrace they would have terrible problems with condensation.
Condensation is a modern problem which has been brought about because we have insulated our homes and made them energy efficient. With all the heat we trap in the home we also trap in moisture, in the past this moisture has been able to escape as properties had draughts. Current building regulations push energy effciency but are now realising that ventilation is key to avoiding the condensation and black mould that forms as a result.
By saying prevent moisture getting into the house in the first place is something I find difficult to understand, you seem to be confusing damp problems with condensation problems. We are the source of the moisture, our clothes on the radiators, breathing, cooking, cleaning and all activities within the home produces moisture. The moisture is produced in the home and the key is to get this moisture out of a property.
We commonly find condensation on the coldest surfaces in a property and insulating that area to bring it up to a temperature equal to the rest of the house can prevent condensation in that area but in most cases will simply lead to a problem in another area.
Change in living habits can prevent condensation, ventilating the house effectively can solve the problem but insulating the home causes the problem in the first place.
To conclude Nick is correct
Hi John, I think I’ve already answered most of the points you make in earlier replies. Landlords often find it easier to blame tenants for condensation than accept that their older, unmodernised properties are cold, darfty, prone to damp problems and unsuited to modern lifestyles. It’s not realistic to expect modern people to live as the Victorians did, and put up with pneumonia and arthritis like the Victorians, just because they live in a Victorian house!
Re your second paragraph, I didn’t say prevent moisture getting into the house, you just made that up. In fact I said the opposite, my flats are so condensation-free I invite tenants to dry clothes on radiators, something most landlords actively dicourage. And how can condensation problems not be damp problems, unless you have dry condensation of course?
Landlords and builders, tend to be a conservative lot and tere is a nostalgic idea that homes of the past were somehow better. The reality is that modern homes are the best they have ever been, more comfortable, dryer, cheaper to heat, as well as having proper foundations and full-sized joists!
Hi Rich,
I believe condensation is a seperate issue to rising or penetrating damp and so was differentiating between the two. Iwasnt trying to say condensation is dry.
“Your first line should be preventing moisture getting into the house in the first pace”
3rd line down on your first response.
I agree modern homes are far better than older homes and I agree building regs should continue to provide more energy efficient homes. However building regulations now recognise the need of ventilation because of the increase in condensation due to more energy efficient properties. They are moving away from infiltration ventilation such as air bricks / trickle vents which allows cold air to get into a property unchecked causing draughts etc and moving towards purpose provided ventilation systems.
I would also like to point out that from my experince I lived in a property for a number of years with no condensation issues at all. I moved on and rented it out. Tenant moved in and within 2-3 months when winter came around I was asked to go back to the property to investigate a condensation issue. There was a severe problem and the reason was her lifestyle was different to mine. She was in the property far more regularly than I was and she also had a larger family. I am not saying it is the tenants fault but the fact is they were producing more moisture in the property. This property was double glazed, fully insulated with new central heating etc. The ventilation system I installed solved the problem
Hi John, I thought you meant in the blog, which is about condensation. I agree condensation is a completely separate issue to rising or penetrating damp. I wrote about them in separate blogs to distinguish between them. Yes I can see I did say that in a response, I think we can agree that keeping rising and penetrating damp out is a sensible move? However water vapour is, as you say, a lifestyle issue and can’t be kept out. Therefore as I see it, you have two options.
Option one: try and change the lifestyle. In my experience it’s quite easy to change my own lifestyle, much harder to persuade others to change theirs.
Option two: build-in adaptations which reduce the conversion of water vapour into condensation by keeping surfaces warm. Warm surfaces will keep the air that comes into contact with them warm. Warm air will hold a much higher moisture content than cold air. In time transpiration means that moisture levels inside seek equilibrium with the lesser levels outside.
Did your ventilation system include a heat exchanger?
I have come to the conclusion that your always right Rob and if you might be wrong you just post confusing replies until your right again.
One last question for you, lets say I have insulated my house top to bottom, 100% insulated. I dry my clothes on rads have no powered extractor fans in bathrooms and kitchens, im living the dream so to speak.
All of a sudden nasty green mould is forming on leather clothes and shoes in my wardrobe. what does one do?
I know, lets insulate the wardrobe.
well????????
sorry I dont know where I got Rob from, lol
Who is Rob?
Extractor fans are mandatory on new developments in kitchens and bathrooms.
If green mould forms on your leather clothes then brush them off and check humidity levels. High humidity is the problem, not condensation unless they are resting against a cold surface. You may need to use a dehumidifier.
High humidity levels mean nothing. you could have 2 properties with a RH70% and depending on temperature have totally different water content in the air and different dew points.
Extractor fans are a form of ventilation and you say ventilation is not key to the control of condensation.
using a dehumidifier defeats your object of insulation which is to keep properties warm, environmentally friendly and save on electric bill.
the mould forming on the leather clothes is formed by condensation, because you have no ventilation and the property is totally sealed and you end up with a high air moisture content. the high moisture levels and poor ventilation cause the water to condense on the leather because they are below the dew point. which in fact is all you have done by insulation the walls is raise the surface temperature above the dew point.
Fact, ventilation and lifestyle change is key to the control of condensation, its is the route cause and to control any type of damp in a property you have to stop it at route. insulating is just masking the problem and moves it on elsewhere.
As for me not living in a modern insulated property, your right I haven’t. But I have inspected 100s over the years and found condensation problems in many of them.
one last thing, I would love to hear you instruct one of your tenants in Pimlico to just brush off the green mould from their £300 Gucci shoes, lol.
anyway I have tried, you will still have to be right of course.
peace
one last thing.
a well insulated property should have a temperature of around 21c now lets say you have no ventilation and occupants are drying washing on rads and creating vast amount of water vapour. if the RH becomes 100% the dew point will also be 21c.
which means pretty much every surface in the property would become affected by condensation.
think about it
I’m surprised we are still discussing this but it’s all good for site traffic so I’m sure Pimlico Flats will be happy. I actually think we agree on more than you realise. If you step down from an adversarial stance you may see that.
Paragraph by paragraph:
High humidity levels: That was my whole point about different RH and different dew-points with different temperatures inside and out. That is how transpiration works.
Extractors: Some ventilation is essential to remove moisture. But it can be relatively passive (opening and closing of doors, transpiration) in most of the house. Fans are necessary and mandatory in bathrooms and kitchens.
Dehumidifier: A dehumidifier does not detract from a property’s warmth. A small domestic one uses very little electricity.
Mould on leather: The leather would be at the same or higher temperature than the inside surface of the walls. Hence condensation would form on the walls too if it formed on the leather.
Ventilation: Yes some ventilation is necessary. I disagree that opening windows and installing an expensive, power-hungry, and warmth-wasteful ventilation system is the answer, particularly if it has no heat exchanger. I would not want to live with one and and have cold air pumped into my house at a high cost to my bills.
Modern insulated homes: Yes condensation can form in them particularly in places like window reveals and corners of ceilings. It’s usually down to poor detailing during construction. Without 100% quality control it’s inevitable. With good detailing it shouldn’t happen and is not a problem in my flats.
Gucci shoes: For the record I am not the owner of Pimlico Flats, I wish I was! I am an associate and my flats are in an OK but not top-drawer part of Bristol.
Agreed if RH reaches 100% the dew point will be all surfaces at air temp or lower.
Thanks for your kind invitation to ‘think about it’. I have and these are my conclusions.
if think we disagree on more than we agree.
you believe insulation is the main key to condensation control I believe its lifestyle and ventilation.
considering its my job to know these things and the fact you seem to understand very little about the relationship between RH, dew points, temperature and vapour pressure in the forming of condensation I would argue my conclusion to be right.
Plus the fact all the foremost experts in the field tend to agree with me.
But you will have an answer for this as you always seem to.
Im finished now, its been interesting mate.
Nick you seem to be investing a lot of emotional energy into this. It doesn’t really bother me whether you disagree or not. I suggest for the sake of your blood-pressure that you adopt a similar emotional detachment. There are two points of view expressed, it is for the reader to decide which is more credible and act accordingly. I can only make suggestions, others will do as they will.
You say it’s your job to know about condensation – likewise it’s mine. I have over 30 years in the business and I am constantly updating my knowledge. By keeping an open mind, sometimes I discover things I thought I knew are wrong. Hence my discovery that the commonly held myth that condensation is solely to be dealt with by ventilation is wrong. Some ventilation is needed but it can be quite mild. Heat exchangers can also help to warm the cold air the ventilation brings in. The key is preventing condensation from forming for long enough for the ventilation to work. Keeping surfaces which attract condensation warm will drastically reduce the speed at which condensation forms. This allows relatively passive forms of ventilation to remove the damp air before most of the moisture can condense out.