Damp on joining wall just below porch roof

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Water appears to be getting in causing a stain on the joining wall of our semi detached house.

The wall is never wet or damp to the touch, but the stain has been gradually working it's way down the wall becoming more noticeable.

Inside - you'll see the stain on the joining property wall. The plaster is minimally raised in parts to the touch, but doesn't appear to be seperating from the wall at all.

Exterior - there is a gap on both the porch roof and a vertical gap joining with our neighbours house. It's unclear what purpose these gaps serve, e.g. for air flow. Could this allow a channel of water to go behind the exterior render, especially if it pools on the flat roof?

What could be the most likely cause and options be for repairing?
 

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I think you need some lead flashing to prevent rainwater getting into that gap. A reputable local roofer may do it, or know a local leadworker (a specialist often does leadwork for roofers without that skill).

I think the old render needs to be chipped off and cleaned up first.

Under no circumstances allow a bodger to come near your roof with a sticky tape "cure" that he calls Flashband.

There are websites where bodgers pay to be listed. These are advertisements, not recommendations. Very likely some of your neighbours will have used local roofers and may know a good firm.

Also, check the gutter, roof and any pipes above to make sure water is not dripping on the porch roof.
 
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is your house cavity construction?

Im wondering how the porch roof is cantilevered out

and why is there a joint in the render between the houses -I'm guessing that's in line with the centre of the party wall.

is the party wall a cavity?
 
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I think you need some lead flashing to prevent rainwater getting into that gap. A reputable local roofer may do it, or know a local leadworker (a specialist often does leadwork for roofers without that skill).

I think the old render needs to be chipped off and cleaned up first.

Under no circumstances allow a bodger to come near your roof with a sticky tape "cure" that he calls Flashband.

There are websites where bodgers pay to be listed. These are advertisements, not recommendations. Very likely some of your neighbours will have used local roofers and may know a good firm.

Also, check the gutter, roof and any pipes above to make sure water is not dripping on the porch roof.

Thans for your advice. I do actually have some of that bodgers tape. I was considering adding some some emergency adhesive flashing in the meantime - I take it that's not a good idea? I will try and find a reputable roofer that can quote to repair, it sounds like it's not something thats easily DIYer by just filling with some mastic/masonary filler? Obviously the render has seen better days, but stopping the water getting in is the main area of concern at the moment. What would your very rough estimation of cost be to repair?
 
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is your house cavity construction?

Im wondering how the porch roof is cantilevered out

and why is there a joint in the render between the houses -I'm guessing that's in line with the centre of the party wall.

is the party wall a cavity?

The house is of Laing Easiform construction and build in around 1950, so I'm pretty sure it has a cavity wall. Though I'm not sure about the joining wall with the neighbours house - I would assume it's got a cavity, and the builder next door seems to think so too.

How the porch roof is cantilevered I'm not too sure, it is solid in construction seems to be concrete and can support my weight when leaned on. The gap in the top of the porch roof is strange to me. Maybe that's just a way to seperate the roofs with the neighbours a bit more? But seems like a way water can escape into that gap and migrate into the house? I could be way off though, just speculating.
 
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I don't think tape will stick to that cracked, crumbly old mortar.

I wouldn't like to guess at the cost. I would have thought you'd pay for half a day. I've done lead work and it is slow, and not very good, without skill.

It's possible that there used to be mortar between the roof and the bricks and it has eroded or cracked due to thermal movement or frost.
 
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I don't think tape will stick to that cracked, crumbly old mortar.

I wouldn't like to guess at the cost. I would have thought you'd pay for half a day. I've done lead work and it is slow, and not very good, without skill.

It's possible that there used to be mortar between the roof and the bricks and it has eroded or cracked due to thermal movement or frost.

The mortar is a bit crumbly towards the bottom, but it actually looks worse in the pictures. It seems still strongly attached to the wall when giving it a prod.

In one of the pictures it will show a view of our neighbours roof which has a concrete-style flashing/lip on the bottom which looks to be the part that has erroded away on our porch roof.

The house is of concrete construction, so no bricks.

I've been suggested to use a mastic filler to fill both vertical and horizontal gaps, but I don't know if that was by a reputable builder or some bodger. Filling gaps does seems sensible to me, though.

Would using a exterior filler to fill the bottom section and create a new "lip" and re-paint with masonary paint work? Or maybe just using the adhesive tape to cover the vertical gap on top of the porch roof (not crumbly at all, so should adhere well) and partially go up the wall to cover the vertical gap - hopefully this would help prevent water seeping back in?

I have some masonary filler and flashing tape - even if these will only be a semi temporary fix, if it keeps us going through winter then it would be a weight off our minds whilst we find a reputable roofer / leaderworker to provide a more professional and permanent fix. Especially as it's gradually raining more and more now, so anything we can do surely must be better than nothing?

Any suggestions would be greatly appreciated!
 
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