The Condensation Trap


Is It Possible To Prove That Tenant Behavior Is The Prime Cause of Condensation Damp?

Chronic cold surface condensation in a Wimpey No-fines non-traditional property
Chronic cold surface condensation in a Wimpey No-fines non-traditional property

Many landlords still hold the view that where a diagnosis for condensation damp has been made then the assumption can safely be made that occupants are responsible, but how do you prove an occupancy related issue?
Is it enough to note that the tenant was drying washing indoors, had extractor fans turned off or perhaps they weren’t using their heating due to fuel poverty? The simple answer is no, because none of those facts, however valid, deal with the landlords obligations.

In fact there is no known test that can prove that residents cause condensation damp; rather you can only prove this by a process of elimination and exclusion of all other factors. Landlords need to work backwards and first prove that they have complied with their own obligations; they should first ask themselves three key questions:

1. Is the property dry and well insulated?

2. Have we provided an effective means of mechanical ventilation?

3. Have we installed a fully controllable heating system?

A point often overlooked is the requirement to prove that the building fabric is dry. If it is wet then moisture evaporating from the building fabric can add to internal relative humidity levels. Moreover, wet building fabric has a much-reduced thermal value and so is harder to keep heated above dew point temperature. Wet building fabric can be the prime cause of a secondary condensation damp problem and this is often missed. Opening windows is never a good idea and we have been battling this bad advice for years. Telling residents to open up windows and turn up the heating is clearly counter-intuitive. The requirement for a fully controllable heating system ensures that the resident has the ability to adjust room temperatures in every room.

Poorly insulated bathroom bulkhead. If mould forms here is this an occupancy issue?
Poorly insulated bathroom bulkhead. If mould forms here is this an occupancy issue?

If Landlords are confident that they have complied with all three factors then by a process of elimination they can safely arrive at the conclusion that occupancy issues are to blame. Unfortunately the default position we often encounter is that residents are to blame, even in the absence of any meaningful evidence.

Our own pragmatic view formed on the back of hundreds of damp surveys and numerous expert witness cases is that occupants cause humidity but buildings cause condensation.

9 responses to “The Condensation Trap”

  1. Mark Duckworth avatar
    Mark Duckworth

    Interesting article, I like the thought process with this particular problem.

    I normally encourage parties to agree that they both have responsibilities which is often helped when the y are made aware of the basic dynamics of humidity.

    Thank you for the interesting posts.

  2. Joe Malone avatar
    Joe Malone

    Thank you Mark. I think in the last ten years I can only remember 3 cases of condensation damp caused by occupancy issues. One was a fairly obvious housing management issue since we found 9 people occupying a tiny 2 bedroomed house, the others were proven by ensuring that the building fabric was dry and well insulated, ensuring that effective mechanical ventilation was installed and ensuring that the buildings had fully controllable heating systems installed. I would argue that occupants have right to live reasonably in their own homes and this includes the ability to dry washing indoors, if they so wish. If they do this in a room with a running extractor fan then this won’t be a problem. I always carefully weigh each potential cause and give recommendations based on proven defects but there is no single magic bullet for dealing with condensation damp and my recommendations often contain a list of items to be addressed in order of importance. You are right in that both parties have a shared obligation but I learned long ago that pragmatically it is best to install silent and continuous running fans because occupants really don’t want to spend time thinking about their obligations or managing them.

    1. rob noble avatar
      rob noble

      hi – think you have over simplified this – i have years working in social housing & although tenants arent soley to blame but they have a major contributory factor due to life style, it is very multi factorial. yes older buildings are poorly insulated etc & is virtually impossible to improve the u value without spending vast amounts of money etc but in my experience i.e. after fitting expensive extract fans tenants isolate them for whatever reason & they are there to combat condensation & mould growth. tenants need to be on boardbut i garee landlords have a lot to do but unfortunately our housing stock is very old & condensation traps.

      1. Joe Malone avatar
        Joe Malone

        Hi Rob, since I’ve covered all factors, building fabric, ventilation, heating and occupancy (multi-factorial), how is it over simplified? Ironically, you then over simplify the problem yourself, by claiming that tenant lifestyle, is a “major contributory factor.” You can say this however many times you want, but it doesn’t make it so. I too worked in social housing for many years, including a role as Head of Asset Management, so I understand the problems with social housing stock, and guess what, it’s no different to any other stock and is in no way unique in the technical problems encountered. You seem to have ignored the premise of the article, which is this… There is no single test that will prove an occupancy related case of condensation damp, and should you ever find yourself in court claiming that your tenant is a major contributory factor, without any evidence, then any competent solicitor will dismiss you, and your claim very quickly. Moreover, it isn’t reasonable or acceptable, to claim, “yes, we have condensation traps forming the majority of our stock portfolio, but since it was built to standards applicable at that time, it’s fine.” Well no it isn’t, and a court would expect you to remedy those defects contributing to condensation. Having old stock will not exclude you from this! The idea, that an expensive extractor fan will always deal with the effects of condensation in old poorly insulated properties is erroneous. Occasionally it will work, but more often than not, other measures are required, and these are applied in a staged and pragmatic manner. Perhaps you can input as to what “life style” choices are such a major factor in condensation? We’ve dealt with two cases of occupancy related condensation damp in the last 10 years. One due to over occupation, the other due to continuous use of an unvented tumble dryer in the property. Cooking, bathing, drying washing indoors, and of course breathing, would not be considered unreasonable behaviour.

  3. Robert Horne avatar
    Robert Horne

    Well what a breath of fresh air. Someone else who actually understands the Lifestyle is not always the sole cause of condensation. I am pleased to meet you.

    1. Joe Malone avatar
      Joe Malone

      Thank you Robert. There seems to be a very common equation applied to these cases, which is: Condensation = Occupancy Issues. Of course this is very convenient not just for landlords but for surveyors who think that all they have to now do is wax lyrical about the benefits of opening windows and turning up the heating. I have carried out hundreds of detailed damp investigations, most of which have involved condensation damp to one degree or another, because of course this is the most common form of damp. Yet, I can only remember three cases of occupancy related condensation damp, one of which related to a clear housing management issue due to the fact that the housing authority had housed a family of 9 in a tiny two bedroomed house. It is always wise to advise occupants on what they do to help the situation but telling the occupant of a Wimpey no fines property to open the windows when there is a fundamental thermal bridging issue is just irresponsible.

  4. Chris Pegge avatar
    Chris Pegge


    Very insightful article. I would be interested in your view on installing humidistat extractor fans instead of timer or pull chord fans in tenanted properties. Providing proper guidance on their use and likely running time. Not as the only measure to reduce condensation but as part of the solution.

    1. Joe Malone avatar
      Joe Malone

      I’m not a fan (No pun intended) of humidistat fans at all Chris. Pragmatically I know that they are incredibly unreliable. The sensors foul up very quickly with dust, which of course it would considering you have an extractor fan drawing dust laden air towards the sensor. I am a great believer in installing silent continuous running centrifugal fans so they run at trickle speed 24 hours a day with boost speed wired to the bathroom lighting circuit.

    2. Joe Malone avatar
      Joe Malone

      Also Chris, I think it’s important to point out that if you’re managing maintenance on social housing properties then you have to overcome the tendency for residents to turn fans off. They think they cost a lot of money to run and of course they don’t. Running continuously about 3 or 4p a day last time I checked. Over run timers simply do not adequate air changes and the key is to manage the heat losses from extraction over a 24 hour period by running continuously at trickle speed. I’m a great advocate of single room heat recovery fans but they’re expensive when compared to a standard centrifugal extractor fan, around £200 compared to £60.00. You must be very specific about the fan you want installed and how you want it wiring. Leave it to the contractor and they’ll install the naffest £10 axial fan they can find!

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