I plan to install about 600 sqft of 3/4 solid red oak flooring but when I removed the existing carpet found that my subfloor consists of 1/2 in plywood with a 3/4 inch layer of particle board over it. I'm going to rip up the particle board but am unsure what I need to put down in it's place. Will an additional layer of 1/2 CDX plywood be sufficient? Also, how should it be fastened to the existing subfloor? Any advice is greatly appreciated.

Yes, 1/2" ply would be perfect. Attach it with screws, staples and/or glue. I prefer 16 gauge staples with a 7/16" crown and 1&1/4" legs. Staple 4" around the perimeter and 6" in a grid pattern in the field. Gap panels approx. 1/8" between each other and 1/2" around the room at the walls. Re-screw the first layer of plywood first to the joists. Install the new panels in the opposing direction and don't marry the seams. Screws work great but are way slower and cost more. No need to use glue unless you want to but I never do.

Thanks, Gary. I'm glad you recommended stapling the new 1/2 ply down and not using glue between the sheets. I really didn't want to spend the time using screws!

However, do I need to put felt or rosin paper between the old and new sheets if I don't use glue? Also, is CDX ply ok to use?

No, you do not have to lay felt between the sheets of plywood. You can, for additional moisture resistance but it would be minimal. Most important to have crawl space DRY and covered with 6 mil plastic vapor retarder. Lay the felt under the flooring and on top of the new plywood. CDX is what is normally used. Make sure it is dry, the CDX, and has been stored inside. Moisture testing should be employed.

1¼" staples are going to blow through the original ½" plywood and lose most of their holding power and then squeak later.

1" fasteners maximum.

Had you had ¾ and putting the ½ over that, 1¼ would be OK.

You misread the thread, Perry. There will be one inch of material under the floor.

My addition says ½ + ½ = 1
1¼, is ¼ more then 1

Meaning the staples will blow through the bottom and protrude ¼"



Are you sure you didn't misread??? They are not talking about the fasteners for the flooring, which after the two layers of ½", 2" flooring fasteners will be the recommended choice.

Problem is guys, 1&1/4" staples are the shortest legs Senco makes for my stapler. I think the idea that if the fastener protrudes through the backside, it loses some (or much) of it's holding ability,has not been shown to me to be true. Whether that fastener protrudes through the back or not, how would that effect the amount of fastener that is in the material? In other words, if a 1" fastener does not protrude but a 1&1/4" faster does by 1/4", how does that extra 1/4" of protruding fastener cause it to have LESS holding power than the 1" fastener that is not protruding. There is still 1" of fastener in the material in both cases. And I seen seen fasteners protrude from the backside of plywood many times. Staples very rarely blast any of the wood away at their exit point. These aren't hollow point bullets we're talking about but skinny pieces (16 gauge) pieces of steel wire. If I can be proven wrong, well, then I learned something but the sceptic in me says "prove it".

Thanks everyone for your replies on this. I'm not sure how the 1 1/4 staples would be less effective than 1" staples but am certainly interested in knowing. I checked my stapler last night and found that it is 18 gauge and it handles 1" staples. My next question now - is it OK to use 18 gauge crown staples with a 1/4" crown or do I need to find a 16 guage crown stapler?

By the way, this message board is an awesome source of information!

Let me see if I can find the books and manuals that I got from Howard Brickman, when I took his classes. It was in there about fastener blow through, somewhere.

That way I don't shoot it from the hip, from my selective memory.

Floorguy - let us know what you find out about "blow through" but I'd still like to know if it's OK to use 18 gauge crown staples with a 1/4" crown and 1" legs. Or do I need to find a 16 guage crown stapler? Basically, is there a difference with using 18 guage staples vs 16 guage?

IMO, there is a difference. I have used both and the 16 gauge is more secure, IMO. You should be able to rent a general construction stapler that uses a 15 to 16 gauge staple with about a 7/16" to 1/2" crown. I have rented them prior to purchasing my Senco SNS 41, which recently has been updated to receive 1" staples.
http://www.senco.com/con_rem/ViewTool.aspx?toolid=550

Could someone please help me understand this a bit more. Is perimeter the outside of the room or the outside of each sheet?

Each sheet