Squeaky floor without a sub floor

Q: My wife and I moved into a rehabbed 2nd floor condo this summer. It was built in 1970, has hardwood floors throughout, and tiles in the kitchen and bathrooms. As we’ve been living here, the wood floors (red oak, I think) have become really squeaky. A little Internet investigation lead me to think that most people with this problem nail the offending board to the sub floor and are done with it. But our problem isn’t just one or two boards, it’s pretty much all of them. Also, I don’t think we have a sub floor.

I think this for two reasons: I installed a ceiling fan this summer and got a good look at the bottom side of my upstairs neighbor’s floor. It looked a lot like the top of my floor, with about 2′ boards with the ends offset. Since the bottom of his and the top of my floor look the same, this makes me think, that both of our floors are just one layer of boards running perpendicular to the joists. The second reason I think there’s no sub floor is that there are rows of nails (in every third floorboard) spaced 16 inches apart running parallel to the joists.

So, how do fix my squeaky hardwood floors? I noticed that some regions of the floor don’t have the rows of nails, and so I assume aren’t nailed to the joists. And the few places where the floor is quiet is where there are lots of nails. Since nails seem to make it quiet, I was thinking of putting more nails into the floor, like maybe at every joist.

Since it seems like a simple solution, I’m a little nervous about adding more nails, because there may be a reason that the original flooring guys didn’t put nails everywhere. Did they nail every third board (and not every board) to let the wood move a little bit? If I nail more regions down, should I also nail every third board?

A: I have seen a few floors like this installed without a sub floor. Sometimes they did not stop the end of the plank at the middle of the joist, but between them. Not a good thing. This floor may be quite old but should have been nailed through the tongue and into the joist. They likely didn’t have a nailer but used simple 2′ common finishing nails. These would tend to work loose over time, especially if there was seasonal movement. You could try a few nails through the face and see if it helps. Counter sink the head and use colour match wood putty to fill the hole. Use spiral nails, not the ones with the smooth shank.