Updating post from Reddit.
I have loads and loads of experience with fixing mould and damp, especially in recent times, across a range of properties. I'm so on the case, fans, PIV, heat recovery, aftermarket trickle vents, checking gutter flows, looking for leaks in the plumbing, improving insulation, taking salt poisoned walls back to render and replastering.
This one is giving me a real headache.
There has been a small amount of damp and mould inside. I have done a thermal and dampmeter survey using a pin dampmeter.
I have also employed an independent damp guy to survey and he found the same results, no external leaks, lots of surface moisture inside.
There is lots of surface moisture where there is mould but nothing at any depth. When the air temp is 19 the walls vary from 14 to 17 c.
So I left a datalogger at the property and it gets to 19-21 every day during the heating periods, they often put it on during the day as well.
The tenant appears to spend a lot of time in their room.
My data logger recorded RH of over 80% all day every day.
Today whilst it was showing 81% in the room I opened the window and put it on the external windowsill for 10 mins, down to 56%. Note it was only 60% downstairs.
I suspect that they are drying washing indoors also, they have a washing line and a tumble dryer. I noticed that the bedroom doors are always closed also.
Is this crazy internal RH solely due to tenants not opening the windows, it does have a condensation latch so it can be left partially open but locked.
I am fitting trickle vents. I have re-iterated that they need to open the window on the condensation latch and for 10 mins a day leave the window open. But I'm kind of at my wits end here as the RH numbers have blown my mind..
Anything I have missed?
edit - I just installed a big compressor dehumidifier, it took a litre of water in 2 hrs, RH down to 67 from 82, the logger showed it was stuck on 80-82 for the last 5 days...
Great post and sounds like an issue experienced by many landlords. I suspect quite a few will be interested in reading the opinions.
I had a similar issue a couple years ago. Turned out to caused by a poorly vented cavity venting into the flat, but that made the humidity high everywhere.
Strange that this is just one room.. Is that room cooler than the rest of the house?
Not particularly, how can I test if its a poorly vented cavity? Also, this has only happened this year, has been fine in the past.
If you've never had the problem before, you've checked everything and it's only come since the tenant has started living there, then it's got to be the tenant. The tenant isn't airing the property to help mitigate the additional condensation they are creating.
Not always - a new leak somewhere can have the same effect if it's then slowly soaking into the building somewhere. It does sound to me suspiciously like it's a tenant inflicted problem but there can be more going on.
Exactly, I'm just mind blown that RH was so high in 1 room.
A good rule of thumb is that with every degree of air temp change %rh changes by 5. So a slight colder room can have massive impact on rh… if the walls are then colder still you’ve got a condensor on you hands. Over time moisture builds up takes longer to evaporate and disperse and the cycle perpetuates.
Solution… open the window / ventilate or as you have said fit trickle vents. Heating alone is pointless as it just evaporates the moisture and allows the air to hold even more but it has nowhere to go so just condenses back once cooled.
Getting about 80% as well. Solid walls, internal insulation with membrane and then plasterboard. Trickle ventilation on most windows.
Humidity outside was previously 70% i think. Its much lower today when i checked.
Tried the German method and left all windows open for 10mins to get rid of all the moist air, then closed so the property isnt being cooled. Seems to worked. Humidity inside is now 63%
Are you sure it's a cavity wall?
I don't think English bond or Flemish bond are used for cavity walls. Only solid walls.
I have had great results with a dehumidifier. I have good double glazing, no trickle vents and just leave the ebac 2650 dehumidifier on an automatic setting.
I monitor humidity in all rooms and also have a smart meter for gas & electricity usage. The dehumidifier uses very little electricity left on all the time and also reduces the gas bill as a dryer room is easier to heat.
Also they have a boost setting that can dry clothing indoors. This works really well and prevents a damp atmosphere even when damp clothing is left out.
Yeah I just installed a compressor dehumidifier, it has made an instant difference.
How much do you reckon keeping the dehumidifier on, on the automatic setting, might cost you for a month?
I have the 25 Litre Meaco Arete one.
It's too hard to give an accurate cost. But really not much at all. It would depend on the humidity and how often the machine automatically comes on. You would also notice a slight reduction in the gas used for central heating as its easier to warm a room at 40% than 70% humidity.