First, let me thank you for such a great site. I built a 15x15ft,all-season room directly off my dining rm. The new room has 3/4in t&g ply subfloor, with the 16" oc joists running north/south. Under the subfloor is insulation held in place with plywood. (I cannot add blocking). The dining room already has a 3/4" oak hardwood floor over a 5/8" ply subfloor, w/ joists running east/west. The present level of both floors match where the hardwood and the new subfloor meet. I want to install 3/4" x 3-1/4" hardwood over both of these surfaces and make it look like one big room. (dining rm wall was knocked out.) My questions are: A) Can I run the new floor parallel to the joists in the new room with only a 3/4" sub and of course continue the install over the present hardwood floor. B) I have a low area on the present hardwood floor (house settling) . What leveling agent would be the best to use and if used what could be the consequences? PS. I'll be doing the install

Only install over existing hardwood, in the opposite direction, or on a 45º.

The other choice is to install plywood over everything, plywood and existing hardwood, to bring it all up to the same level.

Thks Perry, Running the boards in the opposite direction over the present hardwood, will solve the joist directional problem. Since I don't want to raise the floor level any further, is there a method to leveling the low area I have in the existing hardwood floor. (a leveling compound or such) . Harry B

30 lb felt stacks up pretty fast.

The felt paper sounds great. I was afraid I would have to use a liquid leveling compound , and I would have trouble nailing into it. Thanks, Harry