Neighbour's roof water wetting our external walls

They may not be related. Do you regularly open the windows to get fresh air in the room, as high humidity suggests lack of ventilation. The blockage could be causing the rainwater to spill onto the wall, and that would either wet, or cool the wall there.
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Its a good possibility that there will be some moisture getting in because the pipe is almost certainly blocked and its flooding the area.
You could also find that it is a cold spot in your roof and
difficult to insulate ie. prone to condensation.
Thank you for your help guys. We've been here for a couple of years now and every autumn/winter morning, the room double-glazed windows have severe moisture running down them. We've tried all sorts, including leaving some of the windows partially open at night, but this only helps it a little and also freezes the room. We had a blocked chimney which I thought was possibly the reason, but in spring we got an air-vent put in the chimney breast, so we can safely eliminate that too.

I know people will say it's because we are breathing, but it shouldn't be this's just baffling. :confused:
What you've just said makes a lot more sense. Youi breathe out about half a pint of water a day through your lungs, and if there's no ventilation, then it'll find a nice cold surface to condense onto. When you open the window, the problem eases, so that also prove it's a lack of ventilation problem. Now what's the insulation like in the loft, as a warm bedroom wouldn't suffer quite so badly. Also, which direction does the room face, as north facing walls, are always colder.
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The problem does ease, but only a little. This attic roof has kingspan. The bedroom is Almost south-west facing (more west).
How much Kingspan is in the roof, and is it laid as low down as possible between the rafters, and is there anything across the rafters to stop cold bridging. A southwest facing room should be okay, so I've no idea why you are getting such problems. I take it there is no clothes being dried in the room. You've got double glazing, but is there any moisture in between the panes that would indicate that it's failed.
I'm not sure how much kingspan is in the roof...only know that it's all complete (either 50mm or 75mm)...none missing. The kingspan has most definitely been laid by the workmen as low as possible (literally touching the plasterboards) as they advised there needs to be a gap between the roof slates is to avoid condensation problems. The attic itself and no moisture.

There are no clothes being dried in the bedroom.

I assume "between the panes" is the bit where normally there is air between the glass panels???? If so, then no, there is zero moisture and the double-glazing hasn't failed. All the moisture is on the top of glass. On a bad day, the moisture starts to build from the edges/gasket and spreads to the whole window.
You can reckon that Kingspan is about half the size/depth of normal insulation, so you've only got about 100 to 150 there, and the regs no require 270, so you're well down on keeping the warm room. You could look to add 170mm over the joists, and see how that helps. Yes, you're DG is fine, so nor problem there.
I certainly could add it, but that would mean ripping up a brand-newly decorated attic again, so at the moment, financially this is not feasible. Are you are referring to the roof or loft floor joists?

If I may add, lets say that it's due to lack of loft then why are none of the other bedrooms affected?
Are you are referring to the roof or loft floor joists?
If the loft wasn't being used, then you could have added the insulation on top of the loft floor joists, but you've boarded over them, so you're stuck for now.

No idea why the other rooms aren't affected. You'll need to look round them and try and spot any differences. Who sleeps in the other bedrooms.
The floor joists already have some insulation in them...not sure how much.

If I may add, I may have mislead you a bit for which I apologise, because there is one other room affected - which is the living room. The other 2 bedrooms are occupied by my kids, but there is no condensation or moisture.

FYI, the living room is directly above the bedroom which has the moisture/condensation problem.

I've taken some pics, but getting late for work & will post them later on.
God, this ones tricky. But if you've got problems in the living room, then the excess moisture could be migrating to the room above it, so maybe you need to investigate the living room first. Kids are smaller, and they'll breathe out less moisture whilst they sleep, so maybe you need to sleep in their room for a few nights, and see the result. But I think part of the problems till comes from the inadequate insulation in the loft.
Evening all.

I've got some news....Neighbour and I after discussing the issue got a roofer up there today. He checked it out and there was a tree growing in the gutter/downpipe, which was somewhat blocking it. He's cleared it and now the downpipe is unblocked. My concern is whether this was the reason for the moisture build-up in the front of the house where the living-room and bedroom external wall are.

Anyway as promised, below are the photos of the bedroom and living-room windows this morning. Sorry about erasing some of the photos, but it's just that the neighbours can be seen in the photos and I don't like to post a photo without their permission. As you can see, it's some serious moisture.
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No pictures coming through I'm afraid. But if you've got a similar problem in the living room, then that wouldn't have been caused by the tree.

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