Is this a water stain?

FreshlyCutFlowers

What should I do with this? All the regular 'how to reduce humidity' tips online are basic things without any effects for me.. 

On the opposite wall in this room the plaster has curled up in a few places but I was told nothing to worry about.. Is there maybe humidity in this wall?

What service can I hire to find a solution / the cause?

Edit : also how abnormal is this for a 1900 end of terrace..? I'm getting worried and don't know what to do 

Rosa_Damascena

FreshlyCutFlowers said:

What should I do with this? All the regular 'how to reduce humidity' tips online are basic things without any effects for me.. 

On the opposite wall in this room the plaster has curled up in a few places but I was told nothing to worry about.. Is there maybe humidity in this wall?

What service can I hire to find a solution / the cause?

Edit : also how abnormal is this for a 1900 end of terrace..? I'm getting worried and don't know what to do 

Try to not worry OP. You're doing your best to find out, and a job started is half done.

Mistral001

The flashing looks sound.  But hard to say from just a photo. The roof slope certainly is very low for a tiled roof as has been mentioned, but probably has timber sarking and very old-fashioned bitumen felt underneath and this has prevented water penetration from driving rain.  If it did not have this then you would have noticed a leak the first time it rained with the wind blowing towards the ends of the tiles.  So might not be a water leak staining.  It is hard to say from the photo.  It could be condensation or paint discolouration.

donemedosh

If the roof is poorly insulated this will allow warm air to escape & moisture will build up in the walls & ceiling. Have you thought of getting a local "damp specialist" in to give you a free quote for what needs doing. Then do it yourself. You will at least know then what sort of damp you are dealing with.

ryan7

Looks like condensation to me. 
That swooshing shape is a little odd tho, I wonder why it's taken on this shape? 

FreshlyCutFlowers

donemedosh said:

If the roof is poorly insulated this will allow warm air to escape & moisture will build up in the walls & ceiling. Have you thought of getting a local "damp specialist" in to give you a free quote for what needs doing. Then do it yourself. You will at least know then what sort of damp you are dealing with.

I have no practical skills like this so I'd probably not be able to do it myself but if there is such a thing as damp specialist then maybe that is a good direction..  

The humidity stops building at a certain level but it's generally 10% - 15% above where it should be (according to humidity calculators online) . When it seems stable at 70% i leave the dehumidifier running for a bit until it says 65% but then 5 minutes later it's back up to 70% so I stop the dehumidifier as it seemed pointless. I thought it was just new sort coming too quickly. 

Should I just keep it running? Will that draw it put of the walls or not really? 

FreshlyCutFlowers

Today the temperature outside is lower. 8 degrees instead of 13 and it's moved the indoors humidity down to 62%. That's great and maybe gives someone here a better idea of what is happening? I was hopeful thinking it probably rules out leaky pipes, rising / penetrating damp.. 

I keep the house at just 18 degrees so it is low (because it's drafty, saving some money) and contributing to higher humidity but as mentioned it should be lower than this. 

I'm currently thinking of raising the temp slightly, 19 degrees, and run dehumidifier continuously to see if if it can get moisture out of the walls / roof. 

FreshlyCutFlowers

And now that the temperature is down to 4 degrees, my indoor relative humidity is down to 52 in the same room.

Are these online calculators correct? example: https://www.richard-stanton.com/humidity-calculator/
According to this, my relative humidity should be 29% since outdoors is reporting 70% humidity and 4 degrees.. So I'm way above the expected humidity level.

I THINK this is a good sign and maybe means I don't have a leak but again, not sure if that is a logical conclusion based on this.