Our roofer is completely stumped.

[LHdad]

Our property is in a former mining area of Salford and is roughly 115 years old. We've lived in our house for about 10 years.
The old slate roof was in a sorry state and after a few leaks and being the last in our row to have our roof replaced we decided to bite the bullet. We consulted our next door neighbour (an elderly lady living on her own) about the roofer she used and it turned out to be a friend of a friend. He'd done a decent looking job and charged a reasonable amount. He replaced the batons, felt and slate tiles with clay.
It was some time later we noticed a damp patch appear at the top of the wall. We called him back and he said the chimney wasn't vented properly, so he put in a vent. This didn't solve the issue and the damp patch grew. So he came back and redid the flashing and repointed the chimney. Still the damp patch grew (I was convinced it was growing only when the weather was wet) so we got him back and he said safest thing to do was to remove the stack and tile over it. He also got a plasterer round to remove the damp plaster, install a waterproof membrane and replaster. This actually seemed to do the trick so after a few months we felt it was safe to wallpaper and paint.
In the past couple of months the damp patch has returned and seems to be growing quicker than ever.
Our roofer is completely stumped, but now believes the issue is on our next door neighbour's side. We've asked her and she claims there's no damp on her walls. The thing is, I'm still convinced the damp patch grows mainly when the weather is wet. I've been up in the loft (as has the roofer) and it's bone dry up there. I'm also confused as to why the ceiling is wet as well as the wall. There's no mould, and not really any damp smells.
Attached a picture. Any advice / suggestions is very helpful.

 

[Lacan07]

Our property is in a former mining area of Salford and is roughly 115 years old. We've lived in our house for about 10 years.
The old slate roof was in a sorry state and after a few leaks and being the last in our row to have our roof replaced we decided to bite the bullet. We consulted our next door neighbour (an elderly lady living on her own) about the roofer she used and it turned out to be a friend of a friend. He'd done a decent looking job and charged a reasonable amount. He replaced the batons, felt and slate tiles with clay.
It was some time later we noticed a damp patch appear at the top of the wall. We called him back and he said the chimney wasn't vented properly, so he put in a vent. This didn't solve the issue and the damp patch grew. So he came back and redid the flashing and repointed the chimney. Still the damp patch grew (I was convinced it was growing only when the weather was wet) so we got him back and he said safest thing to do was to remove the stack and tile over it. He also got a plasterer round to remove the damp plaster, install a waterproof membrane and replaster. This actually seemed to do the trick so after a few months we felt it was safe to wallpaper and paint.
In the past couple of months the damp patch has returned and seems to be growing quicker than ever.
Our roofer is completely stumped, but now believes the issue is on our next door neighbour's side. We've asked her and she claims there's no damp on her walls. The thing is, I'm still convinced the damp patch grows mainly when the weather is wet. I've been up in the loft (as has the roofer) and it's bone dry up there. I'm also confused as to why the ceiling is wet as well as the wall. There's no mould, and not really any damp smells.
Attached a picture. Any advice / suggestions is very helpful.

View attachment 14357

so was the stack removed?

 

[LHdad]

so was the stack removed?

Yes, not the chimney breast - just the stack above roof height. Then it was patched over with breathable membrane and clay tiles.

 

[Cherryburn]

Unrelated to the damp, but bear in mind that clay roof tiles are significantly heavier than an old slate roof, especially when wet. It doesn't always cause issues, but it's a lot of extra load on an old structure so it's worth keeping an eye on if you see any sagging on the roof.

Damp proofing membranes rarely solve the problem long term, they just trap any moisture so it can't dry out and eventually it gets forced around the edges. Especially since they'll have used gypsum plaster on top. Chimneys can be hard to diagnose, there's a lot of salts in the brickwork from the years of soot buildup. This can migrate through with even a small amount of moisture, and cause issues with your finish. It's not the first time I've heard of this mysterious chimney damp that gets worse in wet weather though, I can't remember a clear resolution. You wouldn't be being paranoid if you got a second opinion on the roof work, there's lots of details with flashing and joining roofs that can just track water in if they're not done right. And that does look like a lot of water.

If you do completely rule out any issues with the roof, my only other thought is if it's something to do with condensation. Chimneys can be a lot colder than the rest of the house, and attract water vapour from both inside and outside the stack. If your neighbour hasn't redecorated in a while they might still have original lime plaster which lets the moisture escape freely, wheras if your side has been replastered with gypsum then those small amounts of moisture could just build up and build up, and would need a decent amount of time to dry out properly if you stripped it back again. Just a theory.

 

[Lacan07]

so was the stack removed?

So the whole stack has been removed to below the roof and there is now no physical way rain water can get access to those walls?

As Cherryburn has said it could be salts from previous leaks attracting the moisture in the room, has the damp patches increased in size at all?

I had a similar problem and like you removed the stack to loft level.

 

[LHdad]

Correct. At least, not according to the roofer who put the roof on. I've attached a photo of the external roof and of inside the loft. Both seem dry.
I have read a bit about the salts in the bricks and being able to apply something to the brick that will draw the salts out.
I think bringing in another roofer or even a damp investigator might be the best way forward...

 

[Lacan07]

Correct. At least, not according to the roofer who put the roof on. I've attached a photo of the external roof and of inside the loft. Both seem dry.
I have read a bit about the salts in the bricks and being able to apply something to the brick that will draw the salts out.
I think bringing in another roofer or even a damp investigator might be the best way forward...

View attachment 14400

View attachment 14401

Personally I wouldn't waste your money. I would just keep an eye on it and it might gradually dry out. Walls take ages to dry out. Have you got a dehumidifier?

Now that you've eliminated any possibility of water ingress I can't imagine how it could get any worse.

 

[a twig]

Agree with the wait and see, assuming the stack was capped off when it was lowered below roof height, there will be little/no air movement now inside so moisture still inside will take a very long time.

If you aren’t fussed about the draughts you could consider taking a brick out of the stack in the attic to increase airflow and speed things along

 

[LHdad]

Agree with the wait and see, assuming the stack was capped off when it was lowered below roof height, there will be little/no air movement now inside so moisture still inside will take a very long time.

If you aren’t fussed about the draughts you could consider taking a brick out of the stack in the attic to increase airflow and speed things along

This is actually exactly what we've done (see below). We've been waiting, honestly, months to see if it dries out and it hasn't. And with another cold/wet winter round the corner we're really worried. We'll try to dehumidifier, though.

 

[a twig]

Ah great, ahead of the game! Might be worth getting a cheap USB borescope / endoscope thing and using it to peer around inside the chimney - available for usual online tat suppliers for under £20 these

 

[a twig]

Oooh, peering at your most recent photo where that new bit of timber has been somewhat yeehaa’d into the old rafter - what’s going on there? Is that roofing felt hanging down inside the loft space? Is that a potential point for water ingress? Might be the light but looks like water staining on the wall below it?

Edit to add:

And what’s going on with the ridge tile where it meets the hip, is that flashing of some sort jammed in there? Again might be light / camera angles but those ridge tiles sloping down to the left just don’t seem to look quite right

 

[Cherryburn]

This certainly looks like it could have been from an old roof leak, failed flashing around the chimney. Water flows down, picks up corrosive deposits from the chimney as it goes and degrades the brick more than the surrounding area. The fact that your chimney stack now ends below the roof line can be a blessing and a curse. Less to go wrong with the roof itself, but it's now open to your loft space which can actually be quite humid. All the warm, moist air from the house tends to find its way up there and condenses out onto cold surfaces, such as the undersides of tiles or the chimney itself. It could be that the issue is now solved and it just needs to dry out, but if you say it's getting worse in wet weather then that definitely raises an eyebrow. Regardless, it's not really going to dry out with a membrane and gypsum plaster on top, so if that's your approach I'm afraid you'll probably have to take it back to brick again.

Oooh, peering at your most recent photo where that new bit of timber has been somewhat yeehaa’d into the old rafter - what’s going on there? Is that roofing felt hanging down inside the loft space? Is that a potential point for water ingress? Might be the light but looks like water staining on the wall below it?

Edit to add:

And what’s going on with the ridge tile where it meets the hip, is that flashing of some sort jammed in there? Again might be light / camera angles but those ridge tiles sloping down to the left just don’t seem to look quite right

That will be where the roofer has "made good" after taking down the chimney stack, there won't have been rafters there so they've added some timber to fasten the battens to. Roofers aren't exactly known for being great chippies. It won't have much strength but it could work fine how they've done it, it's just another potential point of failure to investigate.

 

[Lacan07]

This is actually exactly what we've done (see below). We've been waiting, honestly, months to see if it dries out and it hasn't. And with another cold/wet winter round the corner we're really worried. We'll try to dehumidifier, though.

View attachment 14415

Walls take longer than months to dry out, if the wall below is modern gypsum plaster you could consider hacking it off and re-plastering with lime and a breathable finish, or even just remove the wallpaper.

Pop your head into the loft every now and again when it gets cold outside to check the black bitumen felt for condensation. That will tell you if condensation is a contributory factor in igniting the salts but I'd be sceptical myself. The warm moist air created down below will be the most likely culprit.

 

[LHdad]

Hi all. Thank you so much for the comments and advice, your time is very much appreciated. We will try with the dehumidifiers and if we have to take it back to brick again we'll do it.

 

[aockenden]

He also got a plasterer round to remove the damp plaster, install a waterproof membrane and replaster.
View attachment 14357

Ok so you’ve learned your lesson now: don’t ever let some yabbo builder cover up an extant damp problem in your house with a sheet of plastic again. If you’re serious about wanting a functional house, re-dedicate yourself to deeply addressing the actual fundamental problems, not covering them up (which simply pushes the problem somewhere else).

If I bought your house in the future, one of the first things I’d be doing is hacking off the (likely gypsum or cement) plaster they slathered on the wall, and then ripping out that ridiculous plastic tarp and chucking it in the skip, then replastering the exposed damp underlying masonry with a clay or lime plaster.