Damp issues

[Sammysees]

I’m hoping someone can help ….. I live in a first floor maisonette (owned). The ground floor below me is a rental. On one corner of my flat I have a terrible damp issue. Black mould. It can’t be the roof as it is at skirting board level not at the ceiling. Would damp come up from downstairs? There is an air brick to outside in this corner. A couple of weeks ago I taped up the air brick to see if that would help but it has made it ten times worse. I do open the window every night as I like to sleep with it slightly open.
Any ideas what could be causing this damp? Downstairs is also having damp issues in the same corner.

Is there a downpipe on the outside wall where the damp is coming in? A leaking downpipe is the most common cause of damp issues, I believe. What is the room below used for? Is it a kitchen or bathroom or living room / bedroom?

Definitely don't tape up the air bricks, and perhaps invest in a dehumidifier to try to dry it out a bit. Can you clean off the black mould using a dilute bleach solution?

Thank you. There is no down pipe on that corner. It is raining now and I can’t see the guttering leaking or anything that would cause issues.
The room below is a bedroom that sleeps 4 people (2 adults and 2 small children). My bedroom is also where the issue is.
It is a puzzle.

Four people in a bedroom is a lot... Do they open their windows and use a dehumidifier? If not, it may be possible that condensation downstairs is the root cause, or exacerbating another issue. Do you keep your window open all day as well as all night? I would try doing so if you don't already.,

What is the construction of the building? Are they solid walls? Is there brickwork with faulty pointing that could be letting in damp? Does the wall face north or east?

NB damp issues have been worse in many cases over the past year due to the excessive amount of rain - walls don't have a chance to dry out. If there is also condensation inside, then there could be damp inside the wall as a result as there is nowhere for it to escape to except into the bedrooms.

Do you have a humidity monitor? You can get them cheaply on Amazon.

I can’t say I have ever seen their bedroom window open. They also do a lot of cooking. Indian family and they keep bringing me food - which I have to say is bloody gorgeous. I do think this may be the issue. It is a north east corner so not really any sunshine either - maybe an hour or 2 first thing. I will have to start leaving my window open during the day. Do you think that will help?
The property is 1950’s and brick built. I will get a humidity monitor and see what it says. I have looked at dehumidifiers but they are quite expensive and bulky for a small flat. I might not have a choice though. Thanks for the tips.

That's almost certainly the cause IMO. Are they also drying laundry indoors? Damp air rises as it is less dense than dry air, so it's absolutely possible that it is coming from downstairs. It may be that they don't realise that they need to ensure proper ventilation of their property. is there anyway you can have a conversation with them about it (without upsetting them of course - you don't want to put them off cooking for you 😉)?

But yes, keep the windows in your place open as much as possible. It will definitely help. Even on rainy days it's likely that the air outside will be less humid than in that corner. Then if you get a dehumidifier, have that on whenever the windows are closed.