isnt that big of deal.Did you open up the whole wall or just a doorway?
Your hardwood should run across the joists not with them.Run the hardwood across the joists in the new room, make a 18"-24" wide border in the dining room and then run the field across the joists.
If the transition is in a doorway, get a piece of 4/4 S4S Oak (or whatever floor is) and make your transition strip the thickness of the wall.
If you opened up the wall the length of the room, you can add 1/4 plywood to the floor, glue and nail the H*** out of it
Or use a belt sander and feather out the 1/4" differance in the floor.
Or if the flooring runs 90 degrees to the transition, glue a few thin strips down to the floor to feather this out, the 3/4 flooring will float over this with out a problem.
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