Chimney breast removal

[dansab]

Hello, I decided to join the forum so I can get a bit of help.
I am looking at removing the ground floor chimney breast that is on the party wall and just want to make sure my ideas are good (always better to ask more experienced people).
The first floor chimney section was already removed years ago by the prior owners. I asked the local Building control and they are not interested if first floor was already removed and the stack is supported.
The chimney breast is 53"x 14" and the existing first floor joists are 2"x 7" at around 12" apart with a span of 3.8m, going into the part wall for support and on the other side on the exterior cavity wall(semi-detached house).
My plan is to extend the joists that sit on the chimney breast into the party wall and overlap them 3 feet with 6 M12 bolts. I looked at trimmer option and decided against it because there are 4 joist that need extending.
Is this enough or should I go 4 feet as is not a big cost difference.

Many thanks in advance for the help.

 

[tony1851]

Do the existing floor joists actually sit on the chimney breast? Usually, there is a trimmer in front of the hearth, spanning between the joists either side of the chimney breast. If there is a trimmer there, you only need to span joists between the trimmer and the party wall.

 

[phatboy]

The spec. I was provided was 3x m12 bolts at 200mm centres, with dog tooth washers, and bolts alternating top then bottom of the joist

 

[dansab]

Thank you both

The spec. I was provided was 3x m12 bolts at 200mm centres, with dog tooth washers, and bolts alternating top then bottom of the joist

How long was the overlap vs the full span of the joists?

 

[phatboy]

How long was the overlap vs the full span of the joists?

Full joist was 4.5m span, overlap was 80cm as I recall

 

[dansab]

Thanks

 

[cdbe]

As already suggested, does the breast actually support the joists - which would be quite rare (because of the fire risk) and even if they did, do you think it's a good idea to stick new ones into the back of your neighbours chimney? As a minimum consider using joist hangers and be aware that often the brickwork at the back of an old chimney is a bit of a mess and may need some work before you attach anything to it.

Personally, I find the worst ones are where the joists run parallel to the breast and the first joist (or rather its 2 halves) do sit in the breast (but at the sides not the front so presumably well away from the flue), you have to get a complete new joist in, and sort out the second joist which always has a big chunk cut out to support the stone hearth - it always has a big sag in it.

This one was massive, the biggest chimney breast I've ever seen in a tiny terraced house.

 

[dansab]

As already suggested, does the breast actually support the joists

I will see what I find when I start digging , currently is all covered on first floor and cannot see from below due to the laths

 

[dansab]

Hi All. Finally managed to get around and remove the floorboards and break down the tiles that were in front of the old first floor chimney.
Seems that my initial plan with overlapping joists is very unlikely due to the amount of electric cables that go through the joists .... so I am back to joist hangers.
The distance from the party wall to the trimming joist is 700mm (27 1/2") and as in the pics goes across 3 joists with 30mm (12") between them.
Would you:
- extend the joists between the trimmer and the party wall x3
- make 2 trimming joist parallel with the party wall


Notes: the pipe is redundant and will be removed. On the right side there are 2 joists next to each other under the timber wall that goes to the loft, nothing underneath(on ground floor)

 

[cdbe]

Just one new joist against the wall, hung off the trimmers, build up the shallow one to take the new flooring, it's adequate for that short span.