Wood floor on top of pine floor questions

I have an old house, and in one room I have a pine floor. I want to put an oak floor on top of it when I finish the room. The floor is fairly level, but I'm not sure "how level" it needs to be to prevent problems with an oak floor on top (squeeking, etc).
Also, the oak flooring instructions say to put it perpendicular to the joists, which would be parallel to the pine (sub)flooring. To avoid problems running along the long edges of the boards, should I run parallel to the joists, perpendicular to the pine?
Thanks! Keith
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Keith wrote:

what do you mean by "fairly level"? level doesn't matter so much as flatness. i have successfully installed hardwood over some pretty rough looking subfloors in remodelling situations. if you have elevation differences between boards of more than 1/8 to 1/4", then you might consider replacing it or skinning it with plywood if you can afford the thickness. otherwise, i'd first screw the pine down to the joists. then use a layer of 30# felt and run the flooring perpendicular to the joists. use lots of staples in the hardwood, like every 6".
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Keith wrote:

I'm not clear on your situation. Does the room currently have a subfloor, with a finish pine floor on top of that? In that case I think you could install the oak flooring (I am assuming you mean oak strip flooring, the real wood stuff that is about 3/4 inch thick) perpendicular to the pine flooring since the flooring nails would be completely sunk in wood (pine and subfloor being a layer about 1.5 inches thick) and if the floor is not springy now, it shouldn't be with an extra layer on it either. However, I've never actually done it. Also, usually adding another 3/4 inch of height will cause all sorts of problems and it would be better to remove the existing finish flooring first and then put in the oak. On the other hand if what you have is just one layer of pine subflooring on top of the joists, and you're putting the oak on top of that, then I would say yes put it perpendicular to the joists and nail into the joists. If you haven't done it before, consult a book or have a knowledgeable friend get you started because there are some subtle but important things to make it come out right. -- H
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Thanks to all who have responded. Some clarifying points, below:

nope, it is

The extra height won't be an issue for the existing doors or transitions to nearby rooms.
Sounds like perpendicular to the joists is the way to go. The floor is fairly flat (I doubt I could find a 1/4" height difference anywhere between two pine boards, maybe 1/8" in some places).
I'll definitely do my research before getting started, this was just a question that had been bugging me in my pre-planning :)
Thanks, Keith
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