Hello all,
Please advice, the existing subfloor is 5/8" plywood and on top of that I am installing 1/2" plywood. Does the staples need to penetrate both sheets of plywood (2" long staples) or the top 1/2" plywood (1.5" long staples) is adequate? The existing subfloor has nails all over (2" O.C) and I am worry that the staples will hit the nails if I go with 2" staples. The 1.5" staples will also go through the top sheet but maybe less of a chance of hitting the nails i think.

Thank you in advance.

What is the thickness of the flooring you are installing?

Stonewood

I am planning to install 3/4" x 3 1/2" thick planks.

The Fastener Schedule, per NOFMA/NWFA states:

2” (50mm) barbed flooring cleat In addition –

2 1/4” & 7d or 8d screw or cut 10–12” apart–
3 1/4” nail, 2” 15 gauge 8–10” preferred.

Ray,

that means the staples will penetrate 2 layers of plywood.

Do as you wish.
I'm just quoting the standard.

use the 2 inch. houses with 3/4 subfloors I use 2 inch, over concrete I use 1.5s ifI had the extra layer of plywood that you do I would definatley use the 2 inch, I feel they would hod better having 2 layers of penetrated by a staple. Plus its recomended by nofma. And as far as hitting a nail holding the plywood down. It really isnt as big of a deal as its being made out to be. I could install 1000 sqft and maybe hit a nail 3 times, It may not even curl up on you when you do, with all that subfloor under it.

Better yet look at it from an inspectors view, If that floor fails (and you use 1.5 staples) Could that be viewed as the installers fault? Ray?

YUP.. simple as that.

Thank you all for your comments and suggestions