Damp patch in ceiling, very confused by what I've revealed after cutting it away.

[GeoffSmith]

Hi everyone, 

 

Hoping someone can help me here, this post will be pic heavy!

 

We bought a house two years ago, a 1904 cottage, which, peculiarly, is a cavity wall home, which is apparently rare for the period. The cavities are filled with the polystyrene beading. During the survey, it was pointed out to us that there was a patch of damp in the kitchen ceiling, just next to the cooker, but the surveyor believed it to be historic, and likely due to water ingress from a broken piece of gutter via the brickwork outside, since the patch is located directly next to where the flat roof kitchen extension meets the original house. The patch always felt damp to the touch, and over the course of the two years we've lived here, the patch has increased in size by about 10%, but has never felt any wetter or dryer. 

 

Here is a picture of the cooker, with the damp area cut out:

 

 

Inside the hole was a load of rock hard black stuff, along with rockwool insulation, and lots and lots of horsehair fibre. What wasn't there was any obvious sign of where the water was coming from. However, there was this enormous vent that ran all the way from the hole to the eaves in the roof - this is a shot looking directly up the hole, there are two of these vents side by side:

 

 

As far as I can tell, there is absolutely no signs of any actual damp. However, the brickwork is completely black. I'm thinking either black mould, which is terrifying, given that this leads into the eaves, directly next to our loft bedroom, or could it be historic soot from a fireplace vent of some kind? 

Here is a picture of the vent from the top, inside the eaves, with the roof felt visible. 

 

 

Everything here appears to be dry and solid, with no real signs of any visible damp. 

 

Here's looking down the vent back into the kitchen:

 

 

Here are a few more shots of the hold and surrounding area - this is directly to the right of the hole, facing back into the kitchen. The RSJ is visible, and it has signs of rust. 

:

 

This shot is directly above the cooker vent - this is the black stuff I was talking about:

 

 

And finally, here is the hole close up:

 

 

On this one you can see the rust on the RSJ, so I assume been some long term ingress of water, but what I don't understand is that nothing in the surrounding area is wet. Not even remotely. It's all nice and dry, and it's frankly a bloody mystery how come this patch of ceiling was consistently damp for over two years. 

 

If anyone has theories they can share with me, I'd really appreciate it. 

 

Thanks for looking

 

G

[ProDave]

Those look like the remains of 2 chimneys, hence the black, that is years of soot.  It looks like the chimney stack above has been taken down and roofed over? (more external pictures might confirm) and the lower internal chimney breast  removed.

[GeoffSmith]

Hi Dave, thanks for replying. Gimme a sec and I'll take some outdoor pictures for you. One moment! 

 

Appreciate the quick response mate

[joe90]

I concur with old chimneys, perhaps “damp” is condensation from cold air 🤷‍♂️

[GeoffSmith]

Here ya go:

 

This is outside, and a couple of close ups. I noticed that there's also a small hole in the soffit box, but there doesn't appear to be any other ventilation on the eaves on this side:

 

 

[GeoffSmith]

In the event it's condensation from cold air, which sounds like a pretty solid theory, does anyone know the steps I'd undertake to solve this? My plan is to replace the ceiling at some point when we redo electrics, so I'd like to fix this problem beforehand!

[joe90]

It might be vented into a cold loft space.

[GeoffSmith]

What determines if something is a cold loft space? For reference, the eaves are BOILING hot. As in, if you're in there for any more than 30 seconds on a relatively normal day, you will start sweating. 

 

The roof of the eaves doesn't have any insulation, but the insulation does begin after the knee wall. In the eaves, the floor is insulated with rockwool, but there are portions that aren't insulated on the floor

[ProDave]

If you can get into the eaves space you should be able to see the top of these old chimneys.  Start by insulating the eaves space with normal rockwool type insulation making sure the tops of the old chimneys are covered. for good measure stuff some down from above.

 

Once all nicely insulated replace the plasterboard with foil backed which is more resilient to moisture.

[GeoffSmith]

Ah, thank you, Dave, that's exactly the kind of advice I was hoping to get - so, to confirm, sealing off these old chimneys from the top is OK practice, or are you saying to just fill the top of the old chimney holds with rockwool?

 

Edited September 5 by GeoffSmith

[joe90]

I know you are supposed to vent a disused chimney but wonder what harm would come if you blocked it off at the top and insulated it 🤷‍♂️

a cold loft has insulation on the bedroom ceilings, a warm roof has insulation up the back of the rood slope.  It sounds like  your eaves are “cold” (but will get hot from sun on the black slates.

[GeoffSmith]

Thanks Joe, that makes sense, appreciate the explanation. In which case, this is a sort of cold roof, because only 80% of it appears to be insulated. Theres a big hole where the water tank used to be, which is accessed via a door in the airing cupboard:

 

 

That is actually where the two chimney stacks are, by the way - directly in front.  Could this be contributing? I wonder if I should close off this hatch at the top there, since the eaves are also accessible via an access panel in our bedroom

Edited September 5 by GeoffSmith

[ProDave]

I would frame and board over that hatch.  Then insulate that new ceiling from the eaves loft access.  At the moment warm air from the house can get up that great big hole, meet the cold air in the loft and it is no surprise condensation can drip down the old chimneys.  In the short term stuff some rockwool down the old chimneys from above and lay a sheet of it over the top of them.

 

You will find your house warmer and heating bills lower when you do that.

[GeoffSmith]

Dave, you're a star, thanks so much, just brilliant. That's all work I can do myself, too, which is a relief. 

 

The funny thing is that the heating bills in this house are so high you'll think I'm lying: 66 quid a day if we leave the intelligent thermostat on 20c for 24 hours a day as it would be intended to run. It's simply impossible to keep the heat in the house, so the boiler just runs continuously trying to top up the heat. With the heating on, and an 8kw wood fire raging, we might be lucky to hit 21c after a couple of hours. Suffice to say that we never run the heating unless absolutely neccessary, and have spent the last two years keeping the heating off until mid-december, and then opening up for two hours a day, which still ends up costing over a fiver, alongside however much wood we end up using in the burner. 

 

I'll be over the moon is this ends up fixing two problems at the same time

 

Thanks again mate, and to Joe, too - much appreciated!

[ProDave]

It will be interesting to see how much difference it makes, but it is like permanently having a very large loft hatch left open.

 

It is also disappointing that the surveyor did not mention it might be a good idea to close off that gaping great hole and insulate above it.

[GeoffSmith]

Agreed, although in his defence, it used to have a boiler tank there. When we moved in we had it all ripped out and swapped for a combi, which freed up that space. I feel like an idiot, because it's so obviously a problem, and for some reason, I didn't even twig that it'd be losing heat. It's right at the top fo the bloody stairs, too, so it's probably sucking everything outof the house as it rises. No wonder the loft bedroom is absolutely freezing in the winter! 

I was putting up a partition wall elsewhere in the house last week and have enough material left over to fix all this up, and had a stroke of luck by finding an unused roll of rockwool in the other eaves space, so hopefully this'll cost me nothing - here's hoping!

[Mike]

All good advice. I'd add that if it looks as though any of the soot is loose / lightly attached, it would be worth sweeping the flues to remove what you can, since soot (and the brickwork) will contain hygroscopic salts that are likely to be contributing to the problem.

 

Alternatively, as this is a cavity wall, presumably the flue projects into the room above? If so then an even better solution would be to remove it, eliminating the condensation risk. Then wire-brush the exposed inner leaf of the cavity (which presumably formed part of the flue), treat with SBR & render & skim it.

[GeoffSmith]

Hi Mike,

 

Thanks for the advice, how would I remove it? To my mind even sweeping it would be an impossible task, since it's so long and so close to the wall. Sweeping from above would also be impossible, because the chimney extends to only a few inches below the roof felt. Enough to squeeze a hand through to take a picture, but nothing else!

 

Part of me was wondering if it's sensible to just stick an enormous amount of expending foam at both ends and thereby sealing it. Sensible?

[Jilly]

Random thoughts:

 

A chimney sweep would clear it. 

 

Don’t forget to wear a dust mask (asthma sufferer here!). 
 

The Period House Manual is very useful for learning how insulation works in old houses.
If there are cold spots which could get condensation, using breathable sheep’s wool can hold water then slowly let it evaporate might help. Rock wool is also breathable, so would be better than spray foam, I think? Others might comment.  

 

I like access panels to see what’s going on (insulate behind) in difficult places. I also have a cheap little endoscope for investigations. 

 

Old houses always seem to have wtf moments as you try to work out what previous builders and occupants have done, and jobs seem to be bigger than you thought to rectify. Be mindful of asbestos and get anything suspect tested. 

A dehumidifier can be very useful and a few hygrometers. 

 

 

Edited September 6 by Jilly

[joe90]

1 hour ago, GeoffSmith said:

how would I remove it?

Well do you need to remove it If you seal both ends? 🤷‍♂️

[GeoffSmith]

That was pretty much my thought process. If I just dump a ton of foam in and then cover the foam with insulation, presumably I can just forget about it?

 

 

[Mike]

13 hours ago, GeoffSmith said:

how would I remove it [the flue]?

It depends what you've got. Conceptually I'd guess it's something like this, but presumably not so obvious - it could be in the corner of the room, an extension of an old upper floor chimney breast, etc. You'd need to compare measurements of the ground and upper floors and determine exactly where it goes. And drill a small hole & use an endoscope if necessary, as per @Jilly's suggestion.

 

13 hours ago, Jilly said:

A chimney sweep would clear it.

This

 

11 hours ago, joe90 said:

Well do you need to remove it If you seal both ends?

It's not essential, but preferable if you never intend to use the flue again and can put up with the hassle. It permanently removes the risk of condensation and drafts, eliminates the chance of hygroscopic salts causing problems, and normally gives a little more usable floor space.

 

As others have mentioned, the alternative is to seal the top (level with the upper floor ceiling and made fully airtight), put insulation over it, and seal the bottom. Fill the flue between with something insulating and non-hygroscopic - commonly EPS beads.

 

7 hours ago, GeoffSmith said:

dump a ton of foam

Foam's not normally recommended, but if you choose to do so, consider the risks first. The top ones I can think of are that it could cause damage as it expands - for example if the structure is weak (minimised by leaving each can to expand before adding the next); it can flow through holes - into the cavity or elsewhere - and cause problems (EPS can do that too, but is more easily removed); and it can later shrink and leave a gap between the foam and the flue sides (so don't rely on it for airtightness - at least not regular foam).

 

Edited September 6 by Mike

[GeoffSmith]

Hi Mike,

 

Thanks for all that info, hugely appreciated. In terms of removing the flue, I meant remove the soot - I believe a chimney sweep would be inadvisable, since both parts of the flue are in the house, so it'd be hard to control the dust. 

 

In terms of at least sealing the flue, could anyone advise me of the best way, if I explain the area a little more.

 

Firstly, the bottom of the flue ends around 200mm from the ceiling, as pictured here: 

 

 

This is taken with a wide angle lens, so the flue itself is actually much smaller than it appears. 

 

What would be my steps for filling this in from the bottom end? The expanding foam causing problems makes perfect sense to me. In which case, could you advise on the steps I'd take to sort the problem on this end. 

 

And finally, and I think this is my biggest problem to tackle, is the top part of the flue:

 

As you can see, it ends directly at the roof felt, and the picture is being taken from inside the flue my hand can only just fit in to take the picture. 

 

With space being at a premium here, what steps should I take to seal this end? 

 

Getting an airtight seal from both ends is beyond my knowledge now that I know I can't cheat it with expanding foam. On that basis, any advice on this would be much appreciated.

 

Thanks so much to the help from everyone for the help up until now, it's been brilliant

[joe90]

I would try to fit a chunk of cellotex or kingspan in the flue both ends and seal it with expanding foam as best as possible around the edges. 

[GeoffSmith]

A cool, simple enough! I wouldn't be able to get 50mm through the gap at the top, but I would be able to get 25mm - could I just double up?