Flatten Old T&G Subfloor
I’m putting a bathroom on an uneven wooden tongue & groove subfloor. The floor is both sloped (~3/4″ over 8 ft) and otherwise uneven (has local highs and lows). There also is not a lot of headroom to spare, so I would prefer to raise it as little as possible.
What is the easiest way to flatten this subfloor? I don’t mind if the overall slope remains, I just want it flat enough to accommodate the finish floor (probably vinyl plank). Some thoughts I had:
(1) Put down a new layer of 1/2″ plywood. (Easy, but I imagine most of the unevenness would remain).
(2) Use a self-leveling underlayment. Anyone have experience for the kinds not requiring lath (e.g. Ardex GS-4)?
(3) Lay out of grid of screws adjusted to proper heights to use as a screed for a for a mortar or other non-self-leveling compound.
(4) Tear out the old subfloor, sister up 2x4s with the joists to make a planar framing surface.
Which of those would be the easiest (and also get the job done)? Does anyone have better ideas?
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