Bathroom ceiling joists question

[Vaultedceilingguy]

Good evening, I am improving my bathroom by removing a false ceiling, and the old and sagging ceiling above it. I've already done that, and am left with just the ceiling joists in situ, and the void above them.

I have a 1910 terraced house, the bathroom is in an original extension off the back, at a right angle. I believe it's called a mono pitch roof. I've attached a pic. I share the extension roof with my neighbour. Mine is the house on the left (the scrappy roof will be done shortly).



So while everything is out, I'm wondering if I can create a half-vaulted ceiling to make the bathroom a little bit more impressive. I propose fixing a wall plate onto the party wall, and connecting new joists to it with adjustable hangars, at an angle that keeps the joists below the purlin and attaching to the ends of the rafters as the current joists do. The ceiling would have a shallower angle than the roof; maybe I could get another couple of feet of height on one side of the room. There's no space for storage up there so if I can grab it, I'd like to.

This is the party wall between the two houses in the picture above. The ceiling joists are currently secured (not very well, some are very loose) between bricks.



And this is the view towards the window:



And here's where those ceiling joists meet the lowest part of the roof, near the gutter:



My suspicion is that the joists just rest on the party wall and are nailed to the rafters. I will check over the weekend that they don't continue through the wall and onto my neighbour's side of the roof. If they do just rest in the wall (held in by mortar and wood I suspect) then they're not structural?

Here's a picture of the whole ceiling/roof.

 

[Vaultedceilingguy]

They're all loose and don't go very deep into the wall. Video here:

https://drive.google.com/file/d/1k9zX8lQyW87atlUCl7BhlUA6IWJYUX_C/view?usp=sharing

 

[catlad]

Possibly only one brick thick that wall and I would think they are attached to your neighbours. Another thing to consider is that ceiling you have pulled down was giving that wall some stability.

 

[Vaultedceilingguy]

Party wall is two bricks thick, I investigated further and the ceiling joists weren't supporting anything other than the ceiling. I've replaced it all now with slightly bigger timbers nailed (with brackets) to a large horizontal timber screwed to the wall. Almost finished insulating and boarding it.

 

[^woody^]

ceiling joists weren't supporting anything other than the ceiling

.... and bracing the rafters and external wall.