I know that removing an old unused chimney from a house is done from the top down.
I'm just wondering if it's even thinkable to remove a mid-section from the chimney, while reinforcing under the first removed layer of bricks taken out (would be at the ceiling of the "top floor" on the diagram) (as it's being taken down) to support the top part of the chimney, around 10 feet of it.
The chimney is not structurally tied to the house.
Is this something that's ever done or am I crazy?
It is 'thinkable' in my opinion, BUT!...
There are (among others, already pointed out) reasons to not to do so. Let me bullet this:
If I were You, I wouldn't bother. Comment by Aloysius Defenestrate makes some sense, but I would hesistate to do so in case of strong winds.
Have you the faintest clue what 10 feet of chimney weighs? "reinforce here" to WHAT exactly, that's going to hold up 10 feet of bricks?
This is a bad, terrible unthinkable idea. Take it down from the top, or hire somone else to take it down from the top, or far enough from the top that you feel comfortable working on it.
Don't kill yourself, or someone else in your house, or do massive expensive damage to your house even if you somehow manage not to kill anyone.
Houses of a certain vintage sometimes have "stub chimneys" that start in the attic, with stovepipes below, but they were structurally supported from below before they were built.
The best support for that 10 foot tall, 2 ton (4,000 pound) column of bricks would be a column of bricks underneath it all the way down to the foundation.
Wait, you already have one of those... ;-)
Safety is a concern but truthfully, I did it! 3- 2X6’s on the floor of the 2nd level. Took out everything below with a sledge. NEVER AGAIN! These guys are correct. Brick is very heavy, dirty and an ass ache. Some things are best paid for. After a year or so, I wet back to the roof and took it down, brick by brick, pass the roofline. Sealed the roof and another 8-10 months took the rest down and out. I saved a boat load of money but would pay to have it done. Up and down the ladder/stairs with a few bricks for weeks just wasn’t worth the saving. Let it be known.....it was removed for a kitchen remodel.
The safest way would be to remove the whole upper part and repair the attic and roof. You might be able to support the 10' with a thick steel plate tied into the roof frame attached to the main support beams of the house. The problem is keeping it in place while you remove the bottom structure and get the new support in place with out it collapsing. good luck
Before doing anything, you may want to have a structural engineer check this. My place was originally designed so the chimney helped to support the main beams. (That eventually failed, either as part of or causing the subsidence of part of the house; that weight is now on a Laly column.) You don't want to take out something holding your house up.
And you don't want to in addition place the weight of the chimney on members which may not be able to carry it, which is what taking out just the bottom would do. If you really insist on that approach, a structural engineer could tell you what needs to be reinforced to survive that new load. No guarantee it's possible.
The house is probably the most expensive thing you own, other than the other Hunan residents. Don't gamble with it.
The counter-suggestion to demolish the whole chimney, working from the top down, makes far more sense to me. Since my own chimney is no longer in use (direct-vent furnace with both intake and exhaust on the side of the house), I had the top of my chimney taken off when I redid the roof, and then did my best to seal the top and bottom so I wouldn't lose basement heat into the attic through it. I would like to take it out completely someday, but having removed a few bricks as an experiment, I really would prefer to leave that job to pros. And while recovering those cubic feet would be nice, I don't really need them, or the hassle involved.
