I have full access under the joist a 2x12 with a full basement.
Floor joist crown.
Not enough for concern.
Then use screws to draw down the crown then set the splicing joist in tight.
Actually the 2x4s could be added after the notch is made and the glue and 8 ft.
Between it and the end joist just 12 inches away there was a 5 8 inch drop.
One of the joists close to the end joist of the house had a very significant crown in it.
If it s really bad you might have to pull the sub floor and plain down the joist but that s not much fun.
This is a crown.
Joists that have severe crowns need to be set aside or some of the crown needs to be trimmed off so the floor remains fairly flat once covered with plywood or oriented strand board.
I am retiling bathroom floor and have a very noticable crown on one joist the other joists all appear level.
Long joist is applied.
The joists that is cut will stay crowned unless acted upon by an outside force though it may drop a teensy bit.
The joist on the other side of the crowned joist was properly level meaning it was in plane with the end joist.
It appears the previous tiler tried to deal with the crown by putting a grout line directly on joist and tilting the tile slightly but it is still quite noticeable.
You need to make sure the hump in each floor joist is pointing to the sky.