I have pine floors on my 3rd floor. the sides of the room have sagged over time (1935 build) and now are very squeaky. I just want to refasten the floors down to the subfloor and/or joists.

Couple questions:
- I plan to just face nail the boards. I plan to drill pilot holes so they dont split, and then face nail with 2.5" nails and countersink them manually with hammer/nailset. That plan is the result of a day of internet research. Please help me.
- What kind and length of nails should I use to achieve my goal and have them hold. A specific nail or an amazon link would be most helpful b/c i know nothing.
- Is this pilothole/facenailing plan the best option? worried about old pine splitting if i use screws.
- Should I try to go into joists or just subfloor. Not sure what's even under these old floors. I cant get to floors from underneath. I also am not great at finding joists - could use help there.

Thanks so much! I need a method and direction to actual materials.

How about using countersunk trim head screws instead of nails. A countersink will drill a pilot hole and countersink. The pilot hole will prevent the screw from splitting the floorboard. This will leave a larger surface hole than a nail will. You can either use a plug or wood filler/putty in the screw holes.

8d cement coated casing nails is what I use trying to hit a floor joist. You would be lucky to have a floor distributor nearby who sells these. A lot of older floors will be loose at the ends of each board, so you can move the ends with your thumb. Be sure to nail loose ends before sanding. Remember that the boards are only nailed on one side during installation. On a floor that had sustained water damage, shrinking after being damp for months, I have used 2 inch power cleats and a Powercleat model 101 with rubber tipped mallet. What a workout! You have one stroke to get the "p" nail to set. The "extra force" if you really swing will push the board down at the same time the power cleat is being set. A 50-C with inch and a quarter power cleats will usually fasten a loose finish floor to the sub-floor if the sub-floor is fastened well. The p nails will blend in with the grain so you hardly notice and have barbed shafts so they hold.