I just moved into a new house (new to me anyway). The floor is a 20 year old maple hardwood floor on the main level. It has a lot of gaps between the boards and is in generally poor condition since the previous owners had several large dogs and the floor got pretty scratched up. Someone clearly used a drum sander on it also, because it's quite wavy in the reflections.

More worrisome is the fact that the floor is buckling in the hallway and in several rooms. Upon further inspection, there is NO moisture barrier under this floor at all.

A few questions:
1. Is there some super secret way to do something that would prevent moisture infiltration without tearing out the whole thing?
2. If not, how much extra work am I looking at trying to reuse the flooring after I tear it out?
3. If I tear it out and some pieces are slightly cupped, I am assuming that I will have to get the finish off of them and let them acclimate before putting them back in. Otherwise, if I put them in cupped, sand and finish, they will eventually cup the other way. Is this a correct assumption?
4. If I do one room at a time, will it be easy to make it look decent, or is it going to be obvious where I left off and restarted?

It's close to 2000 sq ft, so there's a LOT of floor there. If I redo the floor, I am planning on tiling the entry way and the kitchen area since those seem to take the most abuse. So that will reduce the square footage a little bit.

My plan if I rip it out is Aquabar B as a moisture barrier, Woodwise if needed anywhere, no stain, Bona sealer after sanding to prevent grain raise, and two coats of Bona Traffic. This is what I did in one of my previous houses, and it was fantastic. My friend is a violin maker also, and I used a little trick to bring out the "fire" in the wood to make it look like the back of a violin.

My neighbor had the same cupping problem with a fairly new floor. There was no buckling. The pro he brought in said he could sand the floor flat but to prevent the problem from happening again he needed to run a deumidifier in the basement during the non-heating season. What goes on in your basement? Also, the recommendations are to control the humidity within the entire house. And, a vapor retarder (Aquabar-B) doesn't stop moisture migration completely. Controlling the entire house humidity year round is important to keep hardwood happy. Where are you located?

I'm in MN. I've got 2 furnaces and 2 AC units, but I don't know how well these dehumidify in the summer yet since I've only been here 3 months. The humidifier was broken when I moved in, and I put a new one in a couple of months ago. Humidity without it was getting down to 4-5%. Although, when it's this cold, I can't go much above 15-17% without getting condensation on the wood frame windows.

I know there's still some moisture movement with Aquabar, but it's better than nothing at all, which is what I have now.

But, is it worth the extra labor to tear out just to get a moisture barrier in there? Or, would it be better to fill gaps with Woodwise, refinish, and cross my fingers that better control over humidity will prevent problems?

Also note, this is the middle of winter and floor is buckled. What's going to happen when it warms up and the humidity goes up from the current 15% that it's at now? I may have to tear it out to fix that anyway.

Have a professional flooring inspector look at the situation. How wide are the floor boards and how are they installed? A slight amount (.01 inch) of cupping is considered normal. If more than this deal with the moisture imbalance before sanding. Buckled boards will have to be removed....figure out moisture problem before reinstalling. If you sand cupped boards before the top and bottom of the board are within 1% moisture content the boards will crown when they dry.
Did these problems just happen or were they like this before you moved in?Were there any water leaks?

They were like this before I moved in.

As far as previous water issues, the only one I know of was that the foundation in the basement leaked when it rained. They fixed it by sealing the foundation, regrading the yard, and putting in drain tile. If there was enough moisture in the basement to make a difference on the floor above, I would expect that there would be visible damage in the basement with sheetrock, paint, and other things. And there is none.

Basement finished? What about the basement ceiling?

A buckled floor in the winter, heating crack & gap season.
You must have a lot of moisture building in the basement.

A moisture barrier(plastic) under the wood, is going to dry rot your joist and subfloor, if there is that much moisture being trapped in the basement..