You need to do a little more archeological digging still. You need to know the whole construction of the floor before you can decide how best to install something new. I'd take up that plywood piece in the kitchen and see what's under it. It's higher than the surrounding floor, so needs to go. You should also be able to see from there what subfloor is under the original kitchen hardwood. It's too bad the space under your entryway is finished, but I'd still do some exploring from below to see what's under there, and to figure out the fix to stop it from squeaking. Is it drywall below or a drop ceiling? I know it probably seems like a pain to tear out drywall, but if you cut out a clean patch, like 2' x the width of the joists, it'll be relatively simple to repair. Just make sure to cut it down the center of the joists so that there's room to screw the patch piece to it later. Cut the hole under the area that squeaks the most, if you can. Have someone walk on and watch the floor from below to see what's moving. It might be as simple as pounding in a couple shims from below, or face-nailing a loose board from above. You want to find out what's underneath the hardwood. It might be laid directly on the floor joists, or there might be 10" wide boards that the hardwood is nailed to. Another thought is to take out a board in the hallway, since that's not original and you want to replace it. See what the subfloor is there. I am a bit puzzled at why, when you've stripped the kitchen down to the original hardwood, it's still higher than the hallway floor. Is your current surface perhaps not the original kitchen hardwood? Peeling back the plywood area will help determine that. BTW, I haven't heard of that stop squeaking product you linked to, so can't offer any personal opinion. And don't pour self-leveling compound over top of hardwood. It needs to go over plywood.

Glad it is not me installing it!!! What a pain. When nailing with a floor nailer, your nails won't hit the joist, unless your top nailing directly straight downward and not blind nailing at the angle.

I'm curious to see the replies. My son almost bought an older house, 1951, the wood under the carpet is about 2"wide strips looks like solid wood, but seems to have a lot of nails. Is that how it was done back then? I wondered how it would look if he had them finished, but he backed out of the deal after the inspection. We are about to tear out decent wood because the sun has faded it and since it is not a big area it would cost a lot to refinish, and I hear the refinished floor would need to be done again much sooner than a new prefinished. I wish I could take out the old wood in a way that it could be used by someone, but I think it will get wrecked. The store I am using charges $3 sf to install it, the wood price obviously varies. They use their own employees, no subs, and did a nice job on our mbr and hall, so I will use them even though I dont know what an independent installer would charge. My maple will cost $5.54 sf, plus install.

SJ McCarthy, our contract is stated we are responsible for the materials and we pay for the labor. Unfortunately we never met nor discuss with the owner but only discussed in details ( in the proposal) with the project manager who is the solely the carpenter.) We just found out there were a lot of the DETAILS from the proposal were not explained (per the PM,but who knows) in detail to the owner or almost like "bait and switch" - for example like item #2- he spent more time because the owner did not get him another helper to help him- I told him this should not be the customer's expenses-Anyway we are willing to pay for it. The owner was offering to renew and establish a new contract from the original contact ( we felt that he cherry picking the items from the proposal, we marked them up then again he decided not to included) for the unfinished works . Once he agreed in our 2nd meeting (another example: he agreed tiling our study room to be included from the original contact in our 1st meeting then when he write the REVISED CONTRACT- he wants to charge us ), but again we are facing the same old stories-he tried to change the wording. We were burned so many times and now we diligently review line by line knowing the owner's personality. He kept saying he lived by the contract-then I told him then he should honor the low estimated to install our engineering hardwood floor including removing the carpet-in the end he says he would honor but he did not including the cost in the new REVISED contract which we add into it - we are so tired with his games. So now we put a contingency - once we agree with the new contract, no more additional expenses from the previous work was done- and we do agree that we need to be notified first and need both signatures for additional expenses from the new contract. and no more point finger of "not included" since we have discussed in detailed and are in the contract. The new addition has a hardwood floor installed - with Dri-core. Once hardwood floor was installed- they are some areas squeak- we were told by PM -put a marked up then he would fasten without explaining to us-these would be additional ridiculous charges (PM told the owner, too-we told PM that they should explain it to us- ) Regarding the installing the engineering hardwood floor is for our existing rooms(concrete slabs that has plywood already)- we are told just to put a vapour barrier. Is it possible to let me know what brands for the glues have to be moisture resistant ($2/sf) or moisture PROOF ($3/sf).? The manufacture instruction suggests to use Franklin Tongue and Groove adhesive (cross linking polyaliphactic emulsion glue) www.titebond.com -any suggestions? This Applachian engineering hardwood floor - FLOATING only needs GLUE between the wood (tongue and groove per the manufacture manual ) then would be FLOAT - this is not to be GLUE DOWN on our concrete floor (could be glue down if necessary but not in our case). Here is the website- on PAGE 9 http://www.appalachianflooring.com/uploads/general/documents/engineered-installation-guide.pdf We trust the PM and we pay for it- we just want to move on and complete the project-It has been almost 10 months. We have to do what we have to do to protect ourselves now- The owner refuses to install our towel bar in our new shower without charging us, and we told him we will take care them by ourselves. I will update this post and hoping for a better solution. Thank you