There's no joist in the corner of the room

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Hi all,
Starting a new thread as the older problem has morphed slightly. To recap: 22mm square-edged boards are going down first, then 18mm solid oak hidden screwed on top. However, after removing some tiles that represented an old fireplace upstairs, I found that there was no joist continued in the corner of the room, against the wall. The unsupported gap form the next nearest joist is 17cm at most.

01Vf8Ox.jpg


This morning I cleared away some of the rubbish that in there and below joist level, there appears to be some sort of stone/concrete plate. Note the bricks you can see just beyond the cutout joist are all loose and sitting on top of this plinth. I believe this is sitting on top of the downstairs wall but cannot prove it because downstairs has had some interesting plasterboarding done in the past. This seems solid though.

n5RbLgf.jpg


I'm planning on clearing out all that dust and rubble later today to get a good view of things, which is also needed if I'm planning on getting a replacement joist in there. You can see the stonework on the wall is uneven so would need to flatten this out before fitting a joist hanger (or pack it?). But the other thing that occurred to be was once the flooring is down, will that be strong enough to hold weight on top of it? Or should I consider screwing something into the brick in the actual corner to support a new joist section?

Read more for history: https://www.diynot.com/diy/threads/...-with-floorboards.544603/page-2#ixzz6TwYlZrfF
 
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My memory might not be so good as it was a long while ago but I remember having the same sort of problem in our old house when I removed the chimney breast right the way through. I think on the upstairs room there was a box built between the downstairs ceiling and upstairs floor to hold the cement/bricks. I'm pretty sure I just added a section of joist (maybe two) from the wall to the nearest joist. That was to support the floorboards above and the plasterboard below. My mate did the plastering for me and I can remember him taking the **** out of my plasterboard nailing - I’d put a clout every 1/2”! Oh, yeah, it’s coming back now, I also had to use a comb chisel and remove every bit of soot from the brick faces before he plastered. That took me bloody ages.
 
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Hi all,
Starting a new thread as the older problem has morphed slightly.
I cleared away some of the rubbish that in there and below joist level, there appears to be some sort of stone/concrete plate. Note the bricks you can see just beyond the cutout joist are all loose and sitting on top of this plinth. I believe this is sitting on top of the downstairs wall but cannot prove it because downstairs has had some interesting plasterboarding done in the past. This seems solid though.

n5RbLgf.jpg


I'm planning on clearing out all that dust and rubble later today to get a good view of things, which is also needed if I'm planning on getting a replacement joist in there. You can see the stonework on the wall is uneven so would need to flatten this out before fitting a joist hanger (or pack it?). [/QUOT
Just use the plinth to rest new joists on and run it perpendicular to the existing (cut out) one. Loved the comment about morphing ;) I think he's morphed right off now.
 
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Got the dust out of there and the plinth is actually part wooden (left) and part concrete (right):
Y9JqSjqh.jpg

The wood seems secure:
wKFNMxph.jpg


I think, looking at where the chimney comes out, the concrete runs in line with the chimney breast itself. The joist at the edge of the room is not the same as those in the rest of the room - its less deep and seems to be shimmed to come level with the other joists.

If I were to use perpendicular joists (wouldn't these be noggins?), should I be securing them to the wall? Or would I be better cutting a section of ply/floorboard to cover these perpendicular joists prior to putting down floorboards? This would support the new boards which of course are running in the same direction.
 
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About to fit the additional joist and wondered what the risk to the subfloor would be if I just used a parallel joist alone, attached to the one that has been cut out but along its entire length? By the time the skirting goes down there would be around 15cm unsupported in the corner. It has 22mm pine asa subfloor then 20mm solid oak on top of that, hidden screwed in. That should be pretty solid right, ie unlikely to bow/buckle in the corner?
 
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Finally got to grips with this. I looked at the perpendicular supports and it was not making sense to me as the plinth below it was not as uniform as I would have hoped. So I created a frame and coach screwed that together, aside from those sections that ran parallel to the notched joist (just used long wood screws there). Once the frame was tight, I screwed some older floorboards to the joists to get the position and laid the frame in position, finally screwing the boards to the older joists - then drilled 12mm holes for the M12 bolts. Once done, slackened that off, removed the temporary screws in the floorboards and inserted the coach bolts, timber connectors, and M12 square washers.



My socket set has gone walkies but luckily a family member was on hand. And a good job too - the one I borrowed was about 40 years old but had a really long arm adapter which I needed. I must have taken well over an hour and a half to keep going back and forth tightening up. The new supporting joist looks tight and flush now although there is still some play in the coach bolts - I'm going to let it sit for an hour and come back to it later to see if anything gives. I'm assuming I need to tighten as much as I can?



I put all my weight on the new frame and it doesn't creak or budge but I did wonder if I needed to put some noggins to support the notched joist and the nearest good one - not sure if this might twist at all? Once the boards are back down I think this will do the job. The new frame is not completely flush with the plinth so there are a couple of thin wood wedges under it. But it does not appear that it is going to move anytime soon.
 

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