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I need to remove old plywood subfloor from a bathroom (the flooring above it is already gone). What's the preferred/proper way to remove it without damaging the floor joists?

One of the methods I've heard of is to a circular saw and cut through the plywood in between the joists. If that's the case though, I'm confused on how to determine exactly where the floor joists are to begin with (presumably just look for screws/nails?).

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If you find the lines of nails/screws hard to spot, try a magnet. They should be pretty easy to figure out, as they will spaced much more closely along the joists, and should make lines that show you where the joists are.

Don't set your saw too deep - it's problematic to cut where you can't see.

One method is to use a small hole saw and drill around the nails, just the thickness of the floor. Then (after getting the sheet of plywood up) you end up with a bunch of small plywood plugs you can break off the screws/nails fairly easily, and enough nail/screw to get a grip on for removal.

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Cut between the joists, then use a sledge hammer to hit the edge of your cuts. You can usually pop each sheet off the joists with one hit at each end, and one hit on the edge. That is the quickest and easiest way to go about it.

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The best way i found to remove an old subfloor with tons of nails and/or staples is,first rip the floor between all joists. Then take your foot,preferably with a boot on it and stomp right on the cuts you made. Not only will the floor come off the joists but it will pull all the staples/nails with it. A nice clean surface is what you will have. If there is also adhesive you can scrape that off easy using a roof scraper. Just be careful not to gouge the joist too much.

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You mentioned subfloor. Did you mean primary floor? The first floor placed on the joists is called a primary floor. Every plywood floor on top of that is called a subfloor. It's reversed, like being in the basement looking up. If you have a subfloor, take a medium sized pry bar and hammer to get an edge up. Finish prying the board up with a long steel bar also called a manual tamper. Easiest way. Remove nails, or staples afterwards with a 4 to 6 inch curved channelock snip. If you are trying to remove a primary floor; use a cats paw and hammer to remove the nails in one board and lift out. Be careful, as joists will be exposed and falls could happen. I suggest tacking down some scrap wood for stepping. You can cut primary floor around edges with a toe kick saw, or a sawzall; if careful. If you are planning on replacing the same size primary floor or thicker, you can precut around edges with a circular saw set at the appropriate level. It's ok if the blade slightly scores the joists, but you don't want to cut into it. Please follow all safety guidelines for your area, wear glasses, and an approved n-95 mask. you only have one pair of eyes and lungs.

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    Interesting - I wonder if the terminology is a regional thing? Several sources seem to use the term "subfloor" to indicate the first floor placed on the joists. Sources: renohardwoodfloors.com/your-sub-floor-and-you-what-lies-beneath en.wikipedia.org/wiki/Floor#Subfloor_construction hgtvremodels.com/interiors/anatomy-of-a-floor/index.html – Mike B Sep 6 '14 at 4:25
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    In the US, "subfloor" means the floor that is directly on top of the joists. If there is additional sheet goods on top of that floor, it may also be called "subfloor". The finish floor then goes on top of it. – Eric Gunnerson Sep 6 '14 at 4:35
  • Thank you very much Eric. And here I thought Illinois was part of the United States of America for 45 years. Boy was I wrong. I was taught structural engineering from my grandfather at a very early age, back when things were done right and terminology wasn't dumbed down for the masses. I am a second generation flooring installer with 28 years of experience and a degree in business administration. I have a fair understanding of what I answer. Yes, today's carpenters call it all subfloor. Even the Tile Council of America states single plywood or double plywood subfloor structures. However, let' – Matthew Sep 6 '14 at 4:49

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