Red Green wrote in
:

Have a hall where there is unevenness under carpet down part of the
length. There will be new carpet going down eventually. Found that the
subfloor has a joint that is not on a joist. About an inch away. T&G
but it's obviously been ignored many years. Tongue is broken in some
areas.

I plan to put some 2x' from underneath with the face across the joint
and screw the subfloor to it from the top to get the two sides even (I
hope). Then support that 2x with a 2x that is sistered to that nearby
joist. Hoping I can get it pretty even but being in such a conspicuous
place, I think ideally a piece of say luan should go over the floor
before the pad and carpet go down.

This would be fine except that the hallway runs open into the LR area.
Wherever that luan ends a new unevenness is gonna be created I
believe.

Maybe I am overthinking this and once I fasten both sides of the joint
solid, the pad and carpet will consume any slight offset.

Opinions and/or ideas?

I don't think I'm gonna need the luan either since it's padding and
carpet over. Just playing "what if". I know as long as I get it solid I
can always bring out the belt and orbital sander with a low grit.

Thinking afterwards, if I did need the luan, where it ends I could sand
and/or use the flooring pothole filler to taper out.