Edge problem replacing floorboards

[diamondtiling]

Thanks Diamond. Yes thats right. The floor joist is about 20cm away from the wall which stands on the floorboards. The boards run under the wall to the next joist on the other side of it. So I cant cut the boards right upto the wall without undermining the wall structure and floor on the other side. Only possibility I can see is to lift boards at intervals on both sides of the wall, and fit noggins to support the wall, but seems way over the top ( or rather under the bottom!)

Fitting extra noggins is not over the top, take up as much of the boards as you can and fit the noggins for strength, these noggins will then replicate the removed floor so the walls will not lose any integrity. You can then fit 18mm ply and hardi on top.
Reinforce under the wall as you go with your noggins, doing it a little at a time will relieve stress on the walls, do one joist and then another. The wall will not be load bearing if its sitting on timber.