Pulled up the carpeting in the upstairs bedrooms and confirmed what I had learned when redoing the master bath and feared the same was going to be upstairs - the so-called subfloor is 1/2" C-D plywood that's not T&G and has no blocking between seems perpendicular to the joists.
I am looking to put down 3/4" subfloor, probably Advantech. The room I am starting in (which will be my son's nursery ) is 12x12'. I can cut out the old plywood, install blocking between the joists to support the edges, glue and screw the subfloor. A bit of a PIA, but I have done it before and aside from carrying the OSB panels upstairs it shouldn't be that bad.
The problem is that I don't think I can install blocking at the ends which are parallel to the joists. The last joists are 8" from the wall on one side of the room and 6" on the other. The joists are 16" OC.
I know 1/4" plywood is not structurally sound, but do you think I can get away with leaving the strips of old C-D plywood along the two sides and adding 1/4" B-C on top, making sure I
- glue it
- screw it
- stagger the joints
Thoughts?? The hardwood I am planning on putting down is likely 3 1/4" - 4" wide 3/4" thick solid HW and will run perpendicular to the joists.
Going over it with 1/4 would be a waste or time and money.
Two options, go over the 1/2 with the advantec or remove the 1/2 and install the Advantec.
There is no need for blocking at the seams if you use Advantec.
Use constrution adhesive and screw it down with ceramic coated decking screws, it will be more then stuff enough.