I’ll be laying LVP on a wooden subfloor, which is above a conditioned crawl space. Carpeting was pulled up, and there was no other flooring on it but carpet. I believe the subfloor is 3/4” plywood.

I’ve been trying to find out if I need to put down 1/4” plywood over it, staggering the joints, or just put down some type of rolled-out underlayment or vapor barrier.  And I see both recommended doing some web searches.

Anyone have any experience with this? I’ve dragged a 4’ level across the floor, looking for ridges or dips, and didn’t find any with the exception of a couple seams that I power-sanded.

We put down about 1800 sq ft about 2 yrs ago and started with sanding all the seams on existing flooring, just cuz. Underlayment of 3/8” particleboard then the LVP.

You’re going to be better off with 3/8 vs 1/4 I believe. Ours is flat as glass throughout. We like it.

I have hurricane floor where the subfloor is 1x12 pine boards with 3/4" plywood over top. Most places had 3/4 MDF which got tore up removing the staples from the padding. I sanded those spot flat and laid 1/4" over top. My house has a crawl space and I haven't had any issues with the Mohawk LVP flooring I put down 4 years ago.

You might check with the manufacturer.   Their recommendations vary and may also vary by the specific product.

I just did a 5x8 bathroom with 7mm LVP (higher-end Stainmaster from Lowe’s)

The previous flooring was sheet vinyl over 1/2” plywood underlayment, over 3/4” plywood subfloor. (This was part of a full bathroom reno down the studs),

Tore up the vinyl and 1/2” ply underlayment. Inspected subfloor, did not need to level. After plumbing, electrical, drywall finished, laid 1/4” (5mm actual) luan leaving 1/4” expansions gaps. I did not have seams to stagger in such a small space. 7/8” crown staples every 6”