Hey Guys (and Gals)... I'm getting ready to lay 3/4" solid (unfinished) Australian Jarrah in our 100yo home in the next month or so. I am covering about 700sq' of original 7/8" (now about 3/4") x 3.25" T&G heart pine.

This flooring is the subfloor and the finish floor all wrapped into one (common as you know).

I would like advice/opinions on NECESSARY underlayment procedure(s) before laying the new flooring. I will be laying it the same direction (perpendicular to the joists)...longways in the house/rooms.

One room will requiring "leveling" due to settlement in one corner (near a fireplace).

TIA