Previous owner used the pictured method. I'm trying the same, but having mixed success. It does give me more wood to sink screws in from above when I have that option. Any other suggestions?
FWIW, that's not really providing "extra support". The sqeaking is likely do to boards moving relative to one another and that solution would provide a location to anchor them down better. What is the the flooring finish above the particle board?
Above this particular example is carpet. So this technique is not expected to reduce bounce in the floor at all? It does give a nice wide base for driving in screws.
A piece of 2x blocking toe nailed into the top and bottom flanges of the i-joists would be more productive.
The problem is that you really need to locate the EXACT source of the squeak.
It is often nails in the sub floor that have become partially withdrawn from shrinkage and allow the sub floor to then move slightly as loads move around.
A 2x2 sister on the joist at the of ending spot and then some screws can be used to pull the sub floor down tight.
there are also screws designed to break off after being driven through the sub floor into the joist (through carpet usually).
Even thin wedges can usually push the sub floor up enough to stop the movement.
Occasionally a strip of hardwood flooring will have moved enough to create a gap to the sub floor and when THAT strip is stepped on it can squeak on the nails or the next strip of floor.
You can screw down a strip floor, but then need to hide the screw heads.
'Trim head' square drive screws leave about as small a hole to repair as a finish nail (and hold better).
Having someone stand on the spot while repairing from below is often worth the effort (or a stack of cement blocks).