Multi chimney stack construction

[LJDIYs]

We have a chimney stack that is shared with our neighbour, four chimneys belonging to each house.

Our four are all open and in use.

The central wall in the chimney, above roof height (so the party wall between us and the neighbour) had lost a lot of mortar, and the spines between each separate chimney on our side had also degenerated, with the top two to four courses of the spine walls between each chimney on our side falling away.

The perimeter wall going right round the outside of the chimney stack was therefore lacking support.

This week a construction company were instructed to take down the whole stack to 2 courses above roof flashing and rebuild it again the same.

They informed us they would need to put a lead DPC/ cavity tray in it, which we agreed to. They put the tray in a course above where they had taken the chimney down to. It was effectively put on top of the existing central wall and spine walls (between each chimney). See photo.

I then assumed they would build upwards from the tray, on the perimeter walls, central wall and spine walls. They instead put a lintel onto the spine wall the build on top of (I do not understand why, as they could have bricked onto the lead DPC directly, unless perhaps a course had been lost under the tray on the spine but then don't see why they didn't rebuild it before applying the tray). The lintel wasn't fixed into the perimeter wall, unless they bracketed it to it.

Looking at the photo it looks like they placed the DPC with 2 bricks (one row) at one end missing and then realised they would be building at one end onto an unsupported DPC. I have no idea why they didn't replace the missing bricks on the central wall before placing the DPC, or if they didn't want to remove the DPC, cut and pull up a section, brick under it, and then put it back down.

It has now transpired that they then built up the central and perimeter walls of the stack but didn't rebuild the spine walls between the individual chimney.

As they have cobbled outwards (as a single skin with the cobble sat half a brick out) to match the previous design, they have realised that they are going to struggle to get the pots to sit on, so are placing roof slates across the chimney, cutting a hole in them for each individual chimney and then launching onto them.

I think it's nothing to do with the cobbling going outwards (as it returns to same width as lower part of chimney) that they can't place the pots, I think it's because they didn't rebuild the spine walls so have nothing for them to stand on.

They are now suggesting putting small lintels perpendicular to the central wall, effectively where the spine walls would have been had they rebuilt them between each individual chimney, however I don't see how they will now be attached to the chimney as they can only sit inside the perimeter of the chimney balanced across the central wall.

My concerns are:

We rebuilt the chimney as the spine walls had failed, leaving a weak perimeter wall to the stack. We now have a stack with a perimeter wall (albeit with new mortaring) but without spine walls (so effectively single skin with only the one central wall support), so have we achieved anything to structurally improve what we had?

We now have four individual chimney flues which terminate in a shared space in the chimney stack, which will then have 4 individual pots, will the shared space affect draught?

I'm also concerned that sweeping the chimney will be difficult with however they decide to mount the pots?

If they do mount the pots onto roof slates with holes cut in them, I am concerned as the chimney exit space (no longer 4 individual flues) is squared off corners, cutting the slate with a hole will leave corners that rising debris will get caught under preventing it vacating through the pots and be a fire risk, albeit the pots would have always been circular too.

Can anyone see the issues, or anymore, that I am seeing with the spine walls having not been rebuilt? I still don't see why they didn't, we now seem to be relying on a network of lintels which are not tied into the perimeter wall.

If they are proposing tying the final lintels which would replace the spine wall and seem to be an after thought into the perimeter wall of the stack then concrete lintels would show in the final course of the chimney, which I do not want. Am I then being reasonable to argue that we asked for it to be taken down and rebuilt as was and they should build the spine walls (even if it means taking down some of what they have built)?

I can't bear letting people work on my house for this very reason, but the other half wouldn't let me work on the roof (or the chimney which didn't leak after 100 years of being there) would have been rebuilt exactly as it was.

Appreciate peoples thoughts. It's upwards from the photo that the spines were not rebuilt with then 10 courses of perimeter and central wall rebuilt without the spine walls between each individual chimney.

 

[Mrs Ten Names]

Was the liner installed as part of the work?
If it was, I believe the work should be subject to Building Regulations.

If it's not too late, you could seek the advice of a Building Inspector to see if it is subject to Building Regulations.

 

[ree]

OP,
Come on please - such massive posts are too long for me anyway to bother reading.
Can you condense what your questions are one at a time, & post pics showing the roof/roofs and the chimney stacks?
FWIW:
1. what you are calling "spine walls" are correctly called Flue Feathers. Using the term feather will get you more info on here or the web. Spine walls are part of the house structure not the chimney breast structure.
2. The build in the pic is confusing, & looks like its being badly done.

 

[LJDIYs]

OP,
Come on please - such massive posts are too long for me anyway to bother reading.
Can you condense what your questions are one at a time, & post pics showing the roof/roofs and the chimney stacks?
FWIW:
1. what you are calling "spine walls" are correctly called Flue Feathers. Using the term feather will get you more info on here or the web. Spine walls are part of the house structure not the chimney breast structure.
2. The build in the pic is confusing, & looks like its being badly done.

Thanks. Long and short of it is, flue feathers were there to top of chimney, but they've rebuilt 15 course chimney putting a cavity tray between 5&6 course as shown in pic. They had to put a lintel in on central wall as rather than laying cavity tray on a complete course, some bricks were missing (you can just about see bricks missing from central/ party wall towards front of photo directly under cavity tray.

Will this means gases and smoke can go between our chimney and neighbours? Neighbours chimney will have no draught as blocked above this hole.

Above the tray, the chimney has been rebuilt around the perimeter and party wall, but no flue feathers now exist on top 10 courses...will this be structurally OK on a chimney with cobbling? Also they went to fit pots and no feathers to stand them on. They are now proposing balancing a lintel over second to last course of party wall, to balance the pots on - but this is 4 open in use fire places, sweeping with this collection of cavity trays then lintels then pots seems a nightmare versus flue feathers and pots like we had before it was taken down.

Interested to know your thoughts.

 

[blup]

A simple smoke test should show which flues are in use, but it sounds as if all four will carry the smoke at the point at which the feathers disappear. Maybe the answer is to use flue liners, or rebuild the lot with input from an expert.

 

[LJDIYs]

A simple smoke test should show which flues are in use, but it sounds as if all four will carry the smoke at the point at which the feathers disappear. Maybe the answer is to use flue liners, or rebuild the lot with input from an expert.

Unfortunately this was meant to be a take down and rebuild by an expert at upwards of £4k cost!

I suppose there is a part of me concerned that ever if the smoke carried up and left a clear chimney, carbon monoxide may not behave the same way. Similarly with the hole through to the neighbours, I think a thermosyphon would be created because their side would be colder than the gases in our side, so gases would be drawn into their flue.

 

[Exedon]

Need to be absolutely clear if any of the flues either your own or your neighbours has not got full integrity to its own pot it must not be used.
Flue gas including carbon monoxide can and will leak into other flues.

 

[LJDIYs]

Thanks. The way the builder has left bricks in the course below the cavity tray/ DPC missing has meant a hole through to the neighbours. As suspected an issue.

Totally avoidable. We've repaired several wall areas where here are DPC's (at ground level), as an amateur I would never just not bother replacing missing bricks from a course and whack a DPC on top and keep building upward. I can't see how they will now fix without taking down the top 10 courses they have put on.

Need to be absolutely clear if any of the flues either your own or your neighbours has not got full integrity to its own pot it must not be used.
Flue gas including carbon monoxide can and will leak into other flues.

 

[blup]

Unfortunately this was meant to be a take down and rebuild by an expert at upwards of £4k cost!

I suppose there is a part of me concerned that ever if the smoke carried up and left a clear chimney, carbon monoxide may not behave the same way. Similarly with the hole through to the neighbours, I think a thermosyphon would be created because their side would be colder than the gases in our side, so gases would be drawn into their flue.

I'm no expert hence my suggestion, is it the case that your builders will argue that because the flues "merge" above roof level, it will make no difference which pot they go through? If so very concerning.

 

[LJDIYs]

I'm no expert hence my suggestion, is it the case that your builders will argue that because the flues "merge" above roof level, it will make no difference which pot they go through? If so very concerning.

I'm fully expecting that to be their argument. I see hot gases in a tight flue hit a much wider area with unlit flues causing the gases to cool and drop back down before they exit the pots.

Additionally the chimney that had fairly poor draught before would now effectively have flues which terminate 10 courses lower than they did before.

 

[blup]

I'm fully expecting that to be their argument. I see hot gases in a tight flue hit a much wider area with unlit flues causing the gases to cool and drop back down before they exit the pots.

Additionally the chimney that had fairly poor draught before would now effectively have flues which terminate 10 courses lower than they did before.

If they are truly “specialists” l suspect they have been getting away with. Are/were they going to parge it?

 

[LJDIYs]

If they are truly “specialists” l suspect they have been getting away with. Are/were they going to parge it?

No they weren't. Having raised issues by message, we had the bricky who is a subcontractor (but was party to the conversation) try to turn up today to complete the final course and add some lintels perpendicular to the party wall to balance the pots on.

I've called builder/ owner and he said the subcontractor knows what he's doing. I then said he may be able to build and attractive and relatively ok from a structural perspective chimney, but we also need it to operate safely.

He is going to get the bricky to review it all and remedy if necessary, but only after he said "how did I know the chimney further down was ok" and the chimney might not be safe anyway.

Fortunately we had a survey earlier in the year - we know we need some repointing done in the attic, but the slurry lining is intact through length of chimney elsewhere.

I also feel it's irrelevant to the work issues I've raised with him.

Fingers crossed we get some remediation and I've asked for photos, or to inspect it. I wouldn't know about the issues if I hadn't asked to have a look at it and gone up there. It makes you feel very vulnerable!

 

[Mrs Ten Names]

He is going to get the bricky to review it all and remedy if necessary, but only after he said "how did I know the chimney further down was ok" and the chimney might not be safe anyway.

Fortunately we had a survey earlier in the year - we know we need some repointing done in the attic, but the slurry lining is intact through length of chimney elsewhere.

I also feel it's irrelevant to the work issues I've raised with him.

Absolutely, It's not acceptable to excuse poor workmanship on the improbability that there might be problems elsewhere.

If I were you I'd go all out and get an expert survey before the current work is paid for.
And if that means stopping the closure of the chimney until the expert survey is carried out, so be it.

 

[blup]

No they weren't. Having raised issues by message, we had the bricky who is a subcontractor (but was party to the conversation) try to turn up today to complete the final course and add some lintels perpendicular to the party wall to balance the pots on.

I've called builder/ owner and he said the subcontractor knows what he's doing. I then said he may be able to build and attractive and relatively ok from a structural perspective chimney, but we also need it to operate safely.

He is going to get the bricky to review it all and remedy if necessary, but only after he said "how did I know the chimney further down was ok" and the chimney might not be safe anyway.

Fortunately we had a survey earlier in the year - we know we need some repointing done in the attic, but the slurry lining is intact through length of chimney elsewhere.

I also feel it's irrelevant to the work issues I've raised with him.

Fingers crossed we get some remediation and I've asked for photos, or to inspect it. I wouldn't know about the issues if I hadn't asked to have a look at it and gone up there. It makes you feel very vulnerable!

A builder is only as good as the subbies he employs and this one doesn't seem bothered. They have gone from bad to couldnt care less, but at least you have called them out. As far as i can see best bet, short of not paying them and getting a building surveyor in to review, is that the “gaps” are filled and an approved flue liner is used not the naked flue. Suggesting a lintel to balance tne pots on if that also obstructs the flue is surely cowboy stuff.

 

[catlad]

Sounds like they are making it up as they go along! Definitely don't pay anything until you have at least put a smoke bomb up each of your flues/ fires.