Supporting base of wood/cob wall between 2 joists

[StephenStephen]

Looking up at the joists and floorboards of the rooms above:

The joist lowest in the picture is 170mm by 47mm
The old timber in the middle (supported by prop) is the bottom of a wood frame with cob and lime infill wall between 2 upstairs bedrooms
The joist highest in the picture will be replaced by another 170mm by 47mm joist, closer to the middle timber.
I'm going to end up with:
new joist - 100mm gap - old timber - 40mm gap - new joist

I'd like to support the old timber frame wall between those two new joists, and am thinking of using wooden block between the joists and old timbers, then bolts all the way through, so that it will look like this (literally) back of an envelope sketch:

Is this a sensible way to do this, or are there better ways?
I'm assuming timber connectors would be a good idea between the timbers and blocks?
Is it possible to recommend a bolt diameter without lots of calculations?
Worth mentioning that this timber frame wall has been apparently unsupported from beneath for decades without any apparent movement. It's not possible to get a clear sense of how it might be supported from either end further up the wall.

Thank you for any thoughts, cheers, Stephen

 

[theprinceofdarkness]

You have a good one there! Loads of comments. My first one is are your sure its cob. Cob walls are huge , 24" thick at least, because they are made of mud and straw or chalk and cow dung!!!, so they are very heavy. My guess is that they stud walls (timber framed) with some indeterminate infill, brick/lathe and plaster. . .Which would make them about 6" thick. If the stud wall was built of a wall plate, a horizontal timber, its this piece of wood that is carrying a lot of the weight. the bottom section of the floor above is Georgian/Early Victorian, the upper section is much more modern, 1950s+. Look at that dodgy joist and narrow boards. Interesting point:- It looks like the older floor boards are nailed upwards, into the wall plate?
Back to your problem, Its a solution, but I feel that you will not be able to tighten up the "bolts " enough for them to offer much strength. In any case you need to use 12mm studding (threaded rod) and big thick square metal washers, make the spacers so the end grains is under compression. The main problem is that you need to support the short joist underneath from the tops of the better and new joists. Also I guess that the fixings will be on display. So your solution could be OK, if you cut the excess studding off and paint the metal work gloss black.
Frank

 

[StephenStephen]

Thanks Frank, yes it's a stud wall with a mixed infill in the wooden frame - about 2" thick (just slightly less than the width of the timber) of earth and straw, and looks like lath and plaster on one side, and plaster (no lath) on the other. Possibly original? (late 1700's)
The nail holes you see in the older boards are floorboard fixings into a previous (beyond repair) joist which I removed.
Yes - supporting that old short joist from underneath is the issue.
I do have some (limited) space below, and the fixings won't be visible because the ceiling will be supported by a separate set of joists - lower surface of those will be approx 50mm below lower surface of floor joists - I'd rather not lose much of that below the old short joist, but could afford up to 10mm or so.
Is there some kind of corrugated metal type solution to span across the two new joists and under the old (it could hang over the new if needed)?
Cheers, Stephen