How to Find Source of Damp Ceiling Near Chimney Breast

[matthussey]

Hi,

We moved into our house in March this year. Recently I noticed a shadow on our upstairs bedroom ceiling near to the chimney breast. I had thought it was a shadow from the lampshade but I inspected it a couple of days ago and found that it felt cold. I have a damp meter so I started to prod around and found that the meter goes off the scale (33%). I tried to find the outline of the damp area and it seems to surround the chimney breast like a halo/ring about 6-12 inches wide even going over the bedroom wall and into the landing area. I went up into the attic and found that the back of the plasterboard is damp and I can see a defined outline of the dampness. The area that is damp seems to be pretty well defined. Within the area sends the meter off the scale but move it about half an inch outside the region and it goes down to below 10%, which seems to be the standard when I check areas I am confident are dry, nowhere near the ceiling.
However, what confuses me is what is not damp. The area of ceiling directly around the chimney of about 3-6 inches is not damp at all. The chimney breast itself is not damp above, nor below the ceiling. The walls that contact damp parts of the ceiling are not damp.
I went into the attic to investigate and I cannot work out where the source of the water is. I haven't yet been able to get around to the front of the chimney but I have been able to get to some of the damp areas and inspect them. All wood I can see in the roof looks fine. My damp meter registered the plasterboard as being damp but the wood next to the damp spots was very dry (I did notice that it does seem to have about a mm gap though so not sure if that is why). The insulation material also felt dry. The chimney breast was dry although there were a couple of dry brown water trails on one side but they may have been there for a long time. There are no pipes at all that I can see above the plasterboard.
I went up during some morning rain (not storm level but reasonably heavy) and saw nothing that looked wrong.
Some history:
- some of the ceiling paint in the area that I now know to be damp was cracked and flaking when we moved in 6 months ago. I assume that this means that the damp issue has been going on for a long time. The cracking has not seemed to get progressively worse at all and the mild "shadow" staining I've noticed may have also been there for a while. Our survey highlighted that there were signs of previous water leaks but that none appeared to be current.
- the house is a 50s concrete house with the chimney entirely within our house. It is not shared.
- we have not noticed drips or anything of that matter
- the chimney is in use with a gas back boiler, although not all day and night
- I cannot see any signs of mold, just damp plasterboard
It appears to me that the chimney is the source of the problem but I can't understand why it's damp all the way around yet the chimney and the area immediately near the chimney is dry.
I have read about hygroscopic salts and wonder if a previous leak has left these in a ring around the chimney and they are pulling water out of the atmosphere. I thought these were from coal/wood fire chimneys though whereas we have gas. Also, would they really pull in that much moisture to cover such a large area and all the way through the plasterboard and paint?
I have thought about the flashing failing, but I'd have thought this would have caused the plasterboard near the chimney to be damp too rather than just a ring, plus would be on the side that is failing rather than all around the chimney.
Can anyone advise on further steps to try and find the source of this problem? I don't want to get a builder in who tells me to do flashing, pointing, chimney replacing, roof replacing, etc. without knowing what the cause is. I'd prefer to try and find the source and then get it fixed properly.
I don't have any photos as yet but I've attached a sketched image to hopefully help.
Any advice would be greatly appreciated. If you want more details, please let me know.

 

[joe-90]

The most likely cause is the back boiler venting up the chimney (if there is no liner). The gases condense in the cold part (upper) of the chimney and travel through the mortar joints. Just like a car exhaust drips water before it warms up.

 

[matthussey]

I'd not even considered that. Why would that cause the damp areas to be away from the actual chimney stack though? Would it cause this much dampness too?
I really want to wait for some windy rain to see if I can catch a leak or feel confident that it's not a leak.
If I'm honest, I think it is a leak and I think I know the where on the plaster is the source, just not how water gets there, nor how it moves from there to surround the chimney.
I really know very little though and just want to sort it with minimal cost. Ideally I'd like to diagnose it as much as I can myself and then action a builder to repair.

 

[foxhole]

Dry near the chimney probably as the warm air keeps it dry.

 

[matthussey]

I think I've found a leak. It's not raining so I can't be certain but I managed to get my camera around the front of the chimney, where I can't reach, and some of the wood in that area is a white in places and the front of the chimney looks like water has been coming down it at some point. I guess this looks like the flashing has failed?

I also did some more checks around the ceiling and although I though the damp surrounded the chimney I've found that the damp area seems to be focussed near the front of the chimney and then spread out to the sides. There then seems to be a gap and another smaller damp patch towards the back. I'm not yet sure what causes the one to the back. I'm hoping it's the same cause and that getting the flashing fixes should sort it out.

 

[ree]

Get a roofer to go up on your roof and investigate - ask for pics of any defects that the roofer finds, and pics of any work that the roofer completes.

Why not post pics of the loft chimney (you already have these pics), the lower chimney breast damp areas, and the chimney stack from the ground?

Determine if you have a flue liner?

Does the chimney accommodate more than one fireplace opening? ie. how many terminals are on the stack?

 

[matthussey]

I have attached a few photos.
The ceiling picture actually stands out more than it looks in person.
The pictures from the ground are from the summer. I can take new ones tomorrow but I'm not sure anything has changed and believe this to be a long term problem anyway.
How do I know if I have a liner? I know there is a metal cowl on top like a GC1. There is only one fireplace and terminal.

I'm still a bit unsure what is happening. The white on the wood seems to mainly be on the short joist (is that right?) directly in front of the stack and on the front surface of the piece perpendicular to it near the stack but only on one side. Also, the ceiling marks are not just below that area but spread around most of the stack through the plasterboard. I still don't understand how I have damp plaster at the back of the stack, dry areas of plaster next to the stack and no water leaks down the breast walls.

I can also see a bit of felt in topfront.jpg that seems to hang down a little bit near a small white patch. I don't think the main leak is there but could be another one.

I'm starting to worry now that this is a major problem due to the rot and I'll need extensive, costly repairs. Once the leak is fixed, how do I get that wood replaced? Is it half the roof off?

 

[ree]

Based on the pics i would say that you have a minor problem with water entering thro the flashings or by by-passing them.

There's no evidence of rot.

The chimney construction seems to be of concrete blockwork up to the roofline, and then in brick. Why you have the curious brick projection clearly seen in pic 73.8KB i dont know - its obviously heavily water stained. Does this brick projection return on all four sides of the chimney?

A GC1 terminal often connects to a flue liner.

But you need someone on the roof examining the flashings and flaunching. Perhaps the stack needs re-pointing but its difficult to tell.

 

[matthussey]

The projection is on the front and backs but not the sides. I really don't understand. From the roofline our chimney is identical to all the others in the terrace so I don't think it's a custom thing but no idea what it is. I have contacted a roofer/builder who has worked for me before so hopefully he'll get back to me soon. He had previously advised getting the flashing done but I didn't do it at the time. I'll probably get the flaunching flashing and repointing done just to be sure.

Does the small piece of white in the beam near the slightly lower felt look like a separate leak or just another exit from a flashing /flaunching leak?

 

[joe-90]

The most likely cause is that the ridge tiles are letting in rain just behind the chimney (back gutter), running down the sarking and down into the house. But realistically it could be anything. You need to pay someone. A couple of hundred should sort it.

 

[matthussey]

Is that fixed by doing the flashing or is that a different repair? My builder thinks it's the flashing but he's coming to look tomorrow and quote for things. I've asked if he can look at flashing, flaunching and repointing. His last flashing quote was more than just a couple of hundred.
I'm guessing it'll take a few months of drying out before I know if it has worked.

 

[joe-90]

Unless the lead has got holes in it it isn't the flashing other than to re-fix it, which would take about an hour. Flaunching is an easy job as is re-bedding ridge tiles. If he can't do it in six hours for 120 quid I'd find a new builder.

 

[matthussey]

The much higher flashing quote was for it to be taken away and replaced, which he thought was needed.

I can see how the back of the chimney as an original source makes sense because there seems to be a smaller patch of damp at the back of the chimney and then a larger arc around the front of the chimney. To have any damp at the back I'd have thought that it must at least come in higher up the roof because water doesn't normally flow up hill (I am prepared for someone to tell me that this is not the case with roofs). I guess some comes out at the back of the chimney breast and the majority migrates around the breast to the front where most evidence of a leak is. Or there are two.

 

[matthussey]

Just thought I'd say though, I posted on 3 different forums and the help I'm getting here is great and much appreciated.

 

[joe-90]

It could be the soakers that sit under the tiles but even if it is, then it shouldn't cost more than £250. It seems to me he's made up his mind to do a 'proper job' at a proper price. Basically, he could well be looking for work and 'bigging' the job up.