I have a hole in a wooden floor as shown on the picture below.
There are different bumps on the underfloor beneath. There used to be and old furnace installed here before so it's possible that the underfloor has been additionally reinforced.
I've managed to find some leftover wood lying around that is thick enough to fill the hole to the level which the primary floor boards take.
However, at some places the holes in the underfloor are to big, so the the new boards would either bend or float.
Here is a conceptual drawing of the situation:
1. This is how it currently looks.
2. and 3. are the approaches I would choose to take.
Is there a established best practice on how one would approach this problem and what could be the pitfalls?
Making a stable support for the frame is turning into more work that I have anticipated. Some of the boards of the underfloor are having almost 1cm hight differences.
So far, the simples way I found to stabilize the boards was to use wedges and flatten the pointing edge so it serves as a touch point for the neighbor board.