Lifting floor boards

[foresttowndiy]

How do I lift floor boards without wrecking every t&g? I want to put them back after levelling the tops of the joists, room is only 10ft sq but sags 3/4" at middle. Going to make packers then replace boards. Each board has a nail about 3/4" from edge in each joist, jacking free side is simply snapping t&g's as I cant get levers in to start to lift next board. Tried lump hammer on side from underneath but not enough room to swing for a good hit.
Hard to put down in words, I'm sure someone will know what I mean!

 

[ladylola]

Small cirular saw , cordless are ideal because of the thinness of the blade , set not to cut deeper than the board thickness (usually around 22mm) rips down the tongues. Punch the nails through the board on one board will allow you to get a lever such as a thin bolster in to prize it up and the rest can be accessed easily then with wedges and bars.

 

[foresttowndiy]

Punch the nails through, why didn't I think of that...
If I don't punch them all the way through I can pull them once the boards are up.
I already have a start as theres one board loose where the central heating pipes were laid when it was installed.
Interestingly there is still the house gas piping still installed, got outlet points in the walls at side of windows in all rooms, pipework is under floors.
The ceiling downstairs is lat and plaster but it must be overboarded as I can see plasterboard joins.
When I relay the boards should I cut them so the ends are visible beyond plaster (using stirtings to cover ends) or have them just short of the bricks as they are now, I've took all plaster off, sand render, 3/4" thick which was all loose. I can't imagine having to lift them again but taking 9" of plaster off to access boards sounds wrong.

 

[ladylola]

Yes you can punch them halfway or so , and once lifted any nails that are left in the boards should be pulled through from the underside to reduce damage to the face.
Another possibility is to use a reciprocating saw or even a hacksaw blade and cut through the nails, it's much more long winded but doesn't do any damage to the face.
By the way I hope you've labeled each board and drawn up a plan to make refitting easy.
I wouldn't think there is any need to trim the ends of the boards the small gap is fine and they will be stable by now.You probably wouldn't need to remove the plaster if there is a next time as they should lift easier without the tongues unless you are planning to put in loose tongues. It may be an idea to screw a couple of boards in a discrete place such as under the place a sofa or wardrobe lives in case you ever feel the urge to rip the floor up again