Internal brick wall supported by floorboards which have been cut.

29 Nov 2015
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United Kingdom
I am looking to replace the floorboards in upstair bathroom with 22mm ply in order to have a tiled floor.
The bathroom is separated from the toilet by a brick wall which I strongly suspect is original (mid 1930s build).
Now that I have lifted the floor covering I can see that a lot of the original floorboards (145 x 20mm) have been cut for copper pipe runs. I do not know how long ago this cutting took place but as eveything in the bathroom is beige I'm guessing the last refurb was 70s or 80s.
The joists (7 x 2) run parallel to the wall at 400mm centres and the boards are perpendicular running from the toilet area, under the wall and into the bathroom.
The boards and joists are in good condition.
5 of the boards have been cut midway over the joist nearest the internal wall meaning that there is only an inch of board resting on the joist for a length, along the wall, of 600 mm. The wall is to the ceiling but from memory does not support anything other than the lath and plaster ceiling.
At last my questions!
1. Is the 1inch grab enough to support the wall? I've checked under toilet floor cover and no cutting or hacking has been done to the floorboards on that side.
2. If the answer to question 1 is yes, then, in order for me to put ply down, can I extend the 1inch grab to the doorway which would result in the entire length of the wall (1.3 mtrs) been supported by 1 inch grab of the floorboards on the joist?
I should mention that I intend to put some long screws through the already cut boards and down into the joists after I post this question.
Thanks in advance for any advice.
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Its my ignorance but i dont know what a grab is and i dont want to guess.

Why not remove the dividing wall between the bathroom and the toilet compartment, it might free up quite a bit of room? And its possibly only a stud partition?
Thanks for your suggestion vinn. The wall is brick. I have stripped the plaster and tiles and it is very definitely brick.
"Grab" was the only term I could think of to describe how much of the floorboard is still in touch with the joist. The boards are still been supported by the joist but only to halfway across the width of the 2 inch joist, hence the board has a 1inch "grab" on the joist. Sorry for any confusion caused. I don't want to make it into one room as we are a family of 5 and there is only one other toilet in the property. As the upstairs loo is the only place I can get some peace I am reluctant to have to either wait to get in or be hurried out of it☺
Thinking about it, it has been like that for maybe 30 years so I'll assume it'll be OK.
How about I cut the remaining boards off at the edge of the joist furthest from the wall , screw some 4 x 2 flush to the top of the joist and screw the ply into that?
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That will work. We need to do stuff like that quite often in refurbs. Doesn't need to be 4 x 2in - 3 x 2in or indersized CLS will do the job, but use #10 x 3-1/2 to 4in screws (or in metric 5.0 x 70 to 100mm) to fix the extra support to the existing joist
Thanks for that Jobandknock, that puts my mind at rest. I have 4 x 2 for the noggins so will go ahead with that but it's good to know it's more than enough rather than not enough.
I've just bought a box of Turbo ll 6 x 80 screws from Screwfix. A little over 13 quid for box of 100. Thanks again.

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