Chimney stack removal

My daughter and son in law are thinking of having the chimney capped on their 1930s house. I’m thinking it might be better to take the stack down to below roof level and extend the roof over. Any thoughts on the best way to stop the heat removal and cold/damp air supply ‘function’ of a chimney without taking out chimney breasts throughout the house?

Is the chimney on an outside wall?
What is the wall profile? i.e. is the wall itself flat with the chimney on one side or the other or does the chimney interrupt the wall line?

My own house is a 1936 semi. When I moved in there were 2 chimney stacks, one was for the kitchen only and the other originally had fireplaces in each habitable room. Only the living room fireplace was still in use and the chimney breast in the dining room had been removed.

The kitchen chimney was completely removed when we had an extension built that would have covered it. The more interesting story is about the other one.

Our pre-purchase survey revealed that the back bedroom fireplace (boarded up) had no apparent support after the removal on the chimney breast below. It was about the same cost to remove that chimney breast high into the loft and to fit proper supports there or to expose the suspended chimney, make good any defects, fit supports and then make good the dining room. We opted for the former. It greatly increased the useful space in the bedroom. I directed my MVHR exhaust through one of the disused flues.

Two chimney pots are now capped and the other two have cowls. The last chimney is no longer in use but it is not worth the cost of replacing the cowl with a cap. We cannot remove the whole chimney as it is shared with next door. They have now stopped burning fuel and I intend to gradually turn their thoughts to complete removal but they have recently spent money having it repointed on their side.

Meanwhile I would like to cut into the remaining flues on my side of the wall and support the other half of our chimney level with the existing support and then take down the remaining breast at least as far as within the thermal envelope, fitting and insulating a small section of ceiling above the reduced chimney breast. Then as rooms are decorated the remaining brickwork can also go.

We are taking three chimneys down shortly, as part of a full retrofit. Removing them, strictly speaking, requires full planning permission, as it’s not covered under permitted development. If you opt to keep and fill them instead, Leca (by Saint Gobain) is a decent option as it’s relatively low in embedded carbon. It comes in 50L bags or can be blown in, but the latter is usually the method when used for ground floors.

Is that “Leca” the porous pea shingle? I didn’t know that it is available in the UK.

It is extensively used in Norway, where I attended a lesson in building with Leca blocks when I lived there.

Thanks for your thoughts, guys. The chimney is ‘within’ the house, ie the gable wall is ‘flat’. The chimney stack isn’t shared with a neighbour.
With a toddler in the house I don’t think they fancy upheavals internally. And they already have a loft conversion.

A flat external wall is ideal, so when the time is right for them the job can be done. They could consider removing the sections in each room separately as they refurbish or decorate but they will, of course, have to put effort and money into supporting anything above the room in question.

We decided we wouldn’t need our open fire once we did all our people powered retrofit measures (3years still ongoing!). The chimney stack needed some work & also cast a pretty big shadow for proposed pv panels.
And it was the source of a howling draught!

Our trusted roofers removed the outside stack to around 1m above loft floor (~600mm above insulation layer), and made good the hole in roof.

We narrowed the fireplace ‘throat’ with engineering bricks & cement board leaving a breathable gap filled with a modified ‘chimney sheep’ reinforced with 1.5 mm s/steel mesh.

Then filled chimney breast from top with Geocell foam glass bubbles (ex Mike Wye).
It took 5x100 l bags of the 2-4 mm size bubbles level to just above loft insulation level, capped it off with layer of mesh to keep out spiders etc!

Apart from the stack removal it’s a reasonably easy diy job and seems to be an effective insulating breathable solution if you want to keep chimney breast.

Made a huge difference to whole house comfort in removing a major draught!

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Thanks for that. It is good to see successes on the forum. They help to inspire other members. I often wish that people who raised queries would come back later with progress and satisfaction reports.

It’s expanded clay:

as used recently by PPR’s Marianne

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Thanks. That is the product I was thinking of. It was in common usage in Norway in the ‘80s.