Trying to decide the best way to approach replacing floor over a concrete slab. There is an existing 5/8” engineered floor (5” planks) that is floating on a padded vapor barrier. I am installing 3/4 solid white oak planks 5in wide. I see two options:

1) Remove the existing floor and put down 3/4 CDX plywood (keep the existing vapor barrier). Attach the plywood with tapcon screws in the center and around the edges. Keep 1/4 gap between sheet edges and 3/4 gap at wall. Install the new floor on the plywood with glue and nails (seems to be the consensus for 5in planks)
2) Install Luan or 3/8in plywood over the existing floor and then install new planks with glue and nails. If going this route, do I glue the plywood to the existing planks or do I put 15# felt paper between the layers? This will create roughly the same amount of subfloor depth but it would not be anchored to the concrete like #1 would be.

It would be less expensive to do #2, but not if the floor then has problems and has to be replaced. Thoughts on best way to approach this?

Thanks

#1 But I'm not a fan of putting a thousand holes in a vapor barrier so I first apply Bostik MVP, 6 mil plastic, optional roofing felt on top of that, then rip the plywood in thirds and stagger laying it diagonally or perpendicular to the floor.
Maybe overkill but never had an issue with moisture.

Thanks for the feedback. Are you ripping the plywood long ways or the short way? Is the goal to allow the hardwood on top to move while attached to smaller bits of plywood? Do you anchor the plywood to the slab? Do you follow the glue and nail approach for the larger plank size?

Thanks again

Ripped it long ways and not anchored. I nailed 5 in Mullican Beech without glue but that was before the new glue and nail rule. Floor moves as a unit and is heavy as heck.

https://www.flickr.com/photos/13772863@ ... ed-public/
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