Please help with this damp patch on my wall

[cdbe]

You could try leaving the adjacent window open a few cm, 24/7 for a few weeks, to prove it in principle first.

 

[JohnD]

View attachment 287892 A bit like this.

I haven't used that type, but the little red indicator looks pretty sensitive. I can't see a bubble.

The objective is to search for almost imperceptible flow, not easily detectable on the digital counter, that does not stop even when everything is turned off, no cisterns refilling.

Turning the inside stopcock off will tell you if a leak is upstream or downstream of it. Turning off the stopcock on the meter will verify if a leak exists. Even a slow drip will cause damp, if it is 24 hours a day 365 days a year. Some leaks are not noticeable as they evaporate into the air (but leave green stain or limescale crust behind). If you see any marks, polish them off and watch to see if they return

 

[dazzler9000]

I wonder if retrofitting some trickle vents in those windows would do the same thing?

 

[JohnD]

Improving ventilation always helps.

 

[foxhole]

It's sealed. I checked this last year.

So it’s not connected to main soffit ?

 

[dazzler9000]

So it’s not connected to main soffit ?

To be honest I'm not sure. I guess it's worth looking up there again one day and taking it apart. I still have the Storm Dry, so if anything, I can coat the brick and reseal the facia. Probably not the best weather now though.

 

[foxhole]

Oh, I see. Yes, I've done a fair amount of research in this area and I do none of the above nowadays (apart from breath), yet I still have high
humidity. I could probably do with opening the windows more rather than first thing in the morning for 10 mins.

I have fairly decent extraction (Manrose MF100T) in the attics for both bathrooms.

I'd love to get MVHR, but I have a few more important things to do first

To be honest I'm not sure. I guess it's worth looking up there again one day and taking it apart. I still have the Storm Dry, so if anything, I can coat the brick and reseal the facia. Probably not the best weather now though.

Don’t see how you can confirm it’s sealed if you don’t know if it’s connected to the rest ?

 

[dazzler9000]

Don’t see how you can confirm it’s sealed if you don’t know if it’s connected to the rest ?

When I was last up the ladder, I checked and it was sealed with some form of sealant. I wasn't checking at the time if it was connected to the soffits, but the image shows that it does screw to the side of the house which joins the facia boards.

 

[foxhole]

When I was last up the ladder, I checked and it was sealed with some form of sealant. I wasn't checking at the time if it was connected to the soffits, but the image shows that it does screw to the side of the house which joins the facia boards.

Having sealant around the outside does not confirm it’s sealed from moisture if it’s open to the main soffit .

 

[dazzler9000]

Having sealant around the outside does not confirm it’s sealed from moisture if it’s open to the main soffit .

Fair enough, I'm happy to investigate. What would you suggest I need to do then? I've never taken apart facia or soffits, so don't know how they should be.

 

[Koolpc]

Put a dehumidifier in the room. Borrow one if you can.

Your humidity is too high. Warm air is attracted to cold surfaces. Especially in external corners.