Condensation and Mould – The Landlord Curse

It is that time of year again when tenants start complaining about damp and mould in their rental property.

As a landlord myself I have been on the receiving end of such a complaint just 3 months after finishing the refurbishment of my first HMO.  My tenant phoned me on the 23rd December just as she was preparing to go away for Christmas to complain of mould.  Guess what my partner Steve and I spent the Christmas break doing whilst my tenant enjoyed her Turkey and Christmas Pud!?

Naive as I was at the time, I educated myself pretty quickly and established that the damp and mould was not because of rising or penetrating moisture but due to condensation.

If the humidity level in the property is over 80% for 6 hours or longer then mould can occur.  High internal relative humidity in a property is the result of poor ventilation.  This makes sense really as you are less likely to see condensation in the warmer summer months when the windows are open.

It is often argued that tenant lifestyle is to blame, but the truth is, most of us create at least 4 pints of moisture per day just by breathing, cooking, bathing and drying clothes, normal everyday activities.  In my 8 bedroom HMO, that’s a whopping 224 pints of moisture every week!  With an extractor hood above my cooker and inadequate extractor fans in my bathrooms as the only ventilation, no wonder I had a problem with condensation.

The argument over whose responsibility it is to ventilate the property is a tricky one.  Landlords often believe that the problem would just go away if tenants open their windows, but one of the reasons why 1 in 5 properties now suffer from condensation is because in our drive for energy efficiency, we have “sealed up” our homes to avoid losing valuable heat.

So how do you spot condensation?

  • Streaming windows and walls
  • Damp areas can appear on walls
  • Wallpaper can start to peel
  • Mould growth, usually black mould, starts to appear on window frames, walls and ceilings
  • Soft furnishings and fabrics become prone to mould and mildew
  • There is a constant musty damp smell in the property

Tips for tenants on how to reduce it….

  • Try to keep the inside temperature reasonably constant for as much of the time as possible
  • Avoid drying clothes indoors and do not dry clothes over radiators
  • Ensure that any tumble drier is property vented or the condensate reservoir regularly emptied
  • Do not supplement heating with paraffin/Calor gas type heating
  • Keep furniture away from walls
  • Do not disable any extraction units

Installing extract fans in the bathrooms and a ventilation unit in the loft area will also solve most condensation problems.  By gently introducing fresh, filtered air in to the home at a continuous low rate, the relative humidity levels are reduced.

Since my first experience with condensation and mould I have gone on to share my knowledge and experience with many NLA landlords, who have also suffered from the ‘Landlord Curse’.

Kim Thorogood is a Specialist Ventilation Adviser at EnviroVent Cardiff, Bristol & Bath.  She is an Accredited Landlord and has been an NLA member since 2007.

For further information visit or telephone 0845 2727 807

For more tips on Condensation and Mould in rental properties, watch our NLA Guide on Controlling Condensation and Mould Growth.

3 thoughts on “Condensation and Mould – The Landlord Curse

  1. Excellent comments. I am always battling with it somewhere. It is difficult to get rid of, I quite agree. What use is a Data Logger as shown on this website in the NLA Guide?

  2. From a tenants perspective, we have extremely low humidity in our rented one-bed (between 25 – 30%, my husband bought a hygrometer and checks it daily), yet have had streaming window panes much of the past year, and horrible spreading mould because of the poor condition of the window frames (rotting, and with glass the thickness of greenhouse glass). I am sure our landlord would love to blame us for the worsening condition of his property, but our experience shows that it is worth considering that the problem may well be in the fabric of the property itself, and have absolutely nothing to do with the tenants residing within.

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