condensation & mould formation

[cotopaxi]

Hi there

I have a flat which I rent out which was built in approximately 1997. The tenants have recently been complaining about condensation around the north facing windows in the living room. This is causing some mould round the window sills (on the walls around them I mean) and appears to be causing some mould on the ceiling. The problem seems to been made worse since we had loft insulation improved last year (went from 100mm to 270mm insulation thickness).

There are no trickle vents on the windows although they are double glazed. The frames are wooden rather than plastic.

I have given the tenants a dehumidifier and urged them to make sure they regularly air the room. I have also asked them to try drying their clothes outside or in another room. I have also bought some anti condensation paint and might apply it after the dehumidifier has been in the room for a while and once all is dry.

I would welcome views on what else I should do and whether this is an issue that will require major investment or is just about tenant behaviour in making sure the property is adequately aired?

Many thanks

 

[jeds]

The starting point is to keep the amount of water vapour going in to the minimum - so avoid drying clothes on rads, avoid excessive house plants etc. Next step is to remove as much of the unavoidable vapour (from showering, cooking, breathing) as possible - by using extractor fans in bath and kitchen and a certain amount of natural ventilation. Bedrooms are often a problem because people give off copious amounts of vapour at night and in the winter people tend to keep doors, windows and vents closed. If the air can't move it will cool faster on cold surfaces and that will cause condensation and mold. If you can encourage tenants to increase air flow it will help. Next step is to search out any specific cold spots. i.e. cold walls, cold sills, etc. These areas will attract condensation (and mold) like a magnet. Improving insulation in these areas has multiple benefits in the long run. The final factor is heating. Most condensation and mold will form at night when it is very cold. Running heating on a low heat through the night can reduce this dramatically. I wouldn't advocate it constantly (personally mine goes off and I like it cold at night) but it can be useful just on the very coldest nights.

 

[JohnD]

... tenants ... condensation ... mould ...no trickle vents on the windows... try drying their clothes outside

with inadequate ventilation, and the tenants adding bucketfuls of water to the air from wet washing, it will never be dry

//www.diynot.com/wiki/building:condensation_in_houses

You could buy them a tumbledrier but they probably wouldn't use it (a typical load costs about 30p in electricity)

 

[^woody^]

In the absence of a defect, condensation mould is always a tenant lifestyle issue

 

[AronSearle]

The areas it is happening in are common cold spots, due to lack of sufficient insulation, the windows may have been fitted in the frame without adequate thermal breaks, and wall insulation often doesn't meet roof insulation leaving corners uninsulated (this is mostly down to ****ty UK standards and building practices).

It's possible that you can improve the ceiling corners by installing rigid foam insulation just around the eaves (making sure not to block ventilation). What can happen is that as mineral wool is rather breathable, cold air blows through it creating colder corners. Either that or add more insulated plasterboard to the ceiling.

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Not much you can do with the windows, and you will still have to manage humidity.

 

[cotopaxi]

Thanks all for your feedback