Need to add 1/4 inch plywood to 1 1/8 inch OSB subfloor. Any advice on which type of plywood to use , and how to attatch to OSB? Am trying to get flush with existing tile. Am putting down 9/16 enginered BC with staples.

Where I'm from, the only 1/4" plywood I can find is an A/C sanded grade, which is better than you need for underlayment. I did find some 1/4" luan for $10.00 a sheet once but that was years ago and I haven't found any since. I'd say, get the least expensive plywood you can find and staple the snot out of it, making sure to keep it flat and without bubbles.

Thanx Gary. Local lumberyard has some 1/4 luan they say is used for underlayment. Will check it out.