Hi folks, hope everyone is doing well.

I am in the process of planning my next flooring install. I have about 900 square feet in a couple of rooms. I am on a slab in Texas and want to float the subfloor. For the last room (only abut 180 sqft), I tapcon'd probably 100+ fasteners to the concrete and it wasn't much fun. To say nothing of the concrete dust!

My question is, is there an advantage to using 2x 3/8 sheets placed versus 2x 1/2 sheets for the floating subfloor. Obviously the 1/2 sheets will be a little stronger, but do I need that much additional strength in a residential application?

Finally, can I expect any flex or give in the finished product? I'm planning on driving 1-3/4" cleats into the floating subfloor to install 3/4"x2-1/4" strips. I am guessing it produces a strong floor with little to no flex, but - except for here and the NWFA guide - there is very little information out there!

Any help is appreciated. Thank you!

Nathan

Half inch would be the way to go. Unless you have height restrictions at a doorway, which probably could be remedied over a small distance. Availability of 3/8ths ply is
another consideration.You may only find A/C grade three eighths inch ply which is expensive vs. half inch CD EX which is used for a lot of different applications
Fasteners that only pass through such a short distance do not hold as well, but you could always use a full trowel to hold the 2 layers together, along with quarter inch head staples which come in different lengths. I would suggest using a lot more staples if going with 3/8ths ply vs. the 6 inch perimeter and 8 inch field recommendation for the half inch ply.
Two layers of half inch CD EX is the best floating sub-floor.

Thanks so much, Pete! I appreciate the quick response. My local plywood house has 15/32 CD exposure 1 yellow pine sheathing. Is this what you are talking about?

Do I need to kerf the backside of the plywood if I am staggering and laying each layer 90 degrees?

Do you recommend cutting the 4x8 panels to 2x8 or 16"x96"? I fell off a ladder and lost a lot of strength in my back.

Also, if I do this, the new subfloor will be slightly less than 1/4" higher than the other room. I don't think this will be a big deal, since it's a tile entryway separating the two. But how do you handle transition pieces? Is this something that I'll need to fabricate? Or do I just use more glue in-between tile and wood areas?

Kerfing should not be necessary. Just what you can handle will be good. I will take more screws or staples to hold everything together. If you need a reducer strip of the flooring material it should be laid on top of the wood flooring adjacent to the tile with the reducer proud of the tile. This will protect the tile edge from chipping if you don't have a factory edge on the tile or if it has a square edge. If you are making it, rip the angle at 15 degrees for a gentle slope with an eased edge next to the tile.
Glue should not be used to build up height under a wood floor. Thin set may work for tile.

Thanks again, Pete, for the quick response. It feels so counter-intuitive not to anchor the plywood to the concrete somehow!

I rarely see straight, flat plywood - even at the plywood house near me. Does the act of gluing and stapling (or screwing) the two sheets of plywood over a large area straighten it out and provide a good base for nailing? And is it reinforced by adding the 1-3/4" cleats when the flooring goes in?

I would hate to get to the end of my project and find that my new wood floor flexes because the plywood was warped.

Anything to help me overcome this fear??? I love the idea otherwise!