Redundant chimney stack

[N_Cook]

Mid terrace houses re-roofed in the 1970s. Main building part of each one, one stack retained and the other removed from ground up through and beyond the roof , nothing remaining except where it had been keyed into the wall in the loft space. But these houses had a minor chimney right at the rear on the rear extension and shared between adjoining pairs. through the ridge of the roofs. Neighbour wants to remove this as a liability. Brickwork removed through both floor levels and partly into loft space, leaving a few bricks cantlilever fashion supporting this small stack. Pots removed then and capped off. Same unsupported situation for both neighbours. Both neighbours agree to its removal. Very few of these chimneys remain now in the area so obviously no conservation/planning issue. No brickwork or roofing problems around this stack. Can anyone think of a structural reason for this partial removal situation in the 1970s or any structural reason now that may come into play if removed totally.? Other than boarding out loft space , to protect ceiling from any dropped brick and dust sheets for general detritus - any tips or sugestions what to look out for when the builders do the removal and then remedial woodwork/sarking/tiles/brickwork/flashing/fire-wall and its sub-coping-slate string course

[Hugo Nebula]

Do I understand correctly; you want to remove the breast on both sides of the party wall and leave the stack on both sides above the first floor ceiling, corbelling the brickwork to support this stack above the roof?

If so, why not remove the stack entirely? This would be the best option. Otherwise, corbelling out the brickwork would have to be done very carefully, and to do it properly would take up a lot of room. Each course should only step out by a 1/3rd of the width of a brick (i.e., 33mm), so you would need ten courses to step it out. All those courses would need to be properly bonded back into the external and party walls.

A far easier solution if you wish to retain the stack is to support it on steel beams at 45-degrees across the corner. 'Gallows' brackets are frowned upon by many Building Control bodies as they rely on the fixing into the brickwork and mortar, which in many old houses is common brick with lime mortar that has been eroded by the nasties from the smoke from the fires in the grates below.

Do I need to mention that you will need to notify you local Council's Building Control about this as it is a structural alteration?

[N_Cook]

It is crudely "corbelled" hence the liability and to confirm - the wishes , both sides, is to have the whole of the stack removed. The part above the roof and the remnant few courses down into the loft space. Building control is a point , need to see that the builder/neighbour has notified+permitted alteration.

[N_Cook]

sub-coping-slate

I have removed several chimneys over the years. It's easier to start from the top and work down, ie leaving nothing. Obviously you have to fix the roof. The main reason being to gain space inside the building but a minor benifit is less likely for the roof to leak. Main problem is sometimes purlins are supported by the chimney and mods have to be made so they remain supported. Quite often too you discover some form of rot in the roof structure too in the process. A snag I have encountered a couple of times is that the back wall inside the fireplace doesn't always line up with the adjacent walls so a lot of brickwork has to be cut back/rebuilt and/or thick coats of rendering,

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Is that rendering required for structural or cosmetic reasons.? The remnant stack is only in the loft space, above and through the roof so appearance is no matter . Lower floors must have been tidied up in the 70s as there is no anomally in wall plaster or ceiling, no sign of a chimney breast having been there.

[N_Cook]

Hide quoted text -

Well both. But it's a lot easier to take the lot down. You often find the outside bit is completely naff anyway. Pointing is shot (inside and out) and the haunching cracked and broken. (Cement bit round the chimney pots.) I took four down on my present house. In every case the worst bit was the misaligned walls at the lower level. If it's at the middle (ie the ridge,) it's no big deal to fill the hole in. Bit harder if it's half way up if you see what I mean. If you leave the chimney on outside, you still have to repair/maintain it as well as thinking of some way to hold it up. A problem if it's all one one side of the wall, ie asymetrical load.

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I've seen that situation somewhere, presumably the owners could not agree to both take down the chimney. So half a chimney, probably more than twice a liability of collapse and an ugly vertical face , ideal for water penetration.