This is my first post, so sorry for an newbie mistakes. I did a little research, but some of the posts didn't apply to my case. I have 4x8 joists 4ft O.C. with a single 1-1/4" TG plywood subfloor. The joints are supported by a perimeter foundation and piers thoughout the center of the house. I really want to install whatever hardwood floor I choose parallel to the floor joists because they would run with the longest walls and a hallway. Will the single subfloor be enough? I am suspecting not. Any recommendations on to what additional plywood thickness I would need? Also if I need to add some plywood, should I run in perpendicular to the existing like you normally would or not? Because then I would need to run the hardwoods parallel to the additional plywood to make it parallel to the joists.

Thanks for the help.

You have 4x8 joists 4ft O.C. with a single 1-1/4" TG plywood sub-floor? That's bizarre. Where on earth are you?

I'm in Oregon. It's a little bit of an older home, 1970. If there is any help it would be appreciated.

If you have that thick of a layer of plywood than running parallel to the joists will not be an issue.

Okay, I wasn't sure because in the kitchen and through a couple of the doorways the floor has a little movement. Would additional plywood help, or just blocking under the floor. I realize that the 4"x8" joist and a single 1-1/4" subfloor is not the norm. Thanks again for the help.

Four feet between is still a huge span even though that thing is built like a monster and you already have a double thickness of subfloor. lol I'd at least block it out. What you don't want is sagging between joists.

I'd probably block it out, and sheet it out with another 1/2" plywood.
Installing parallel to joists ( at normal joist spacing )..... it's recommended to sheet out over a 3/4" subfloor with 1/2",( bringing you to 1 1/4"). 1 1/4" is where your at now, but on top of that you have the joist span to consider, even with blocking.

Thanks guys for the advice. The 4 ft span between joists is pretty big to modern building standards. I will block in between the joists in the "soft" spots. I guess I will go back to one of my original questions. If I put down 1/2" perpendicular to the existing 1-1/4" TG subfloor, it will be parallel to the joists, and that is the direction I want to lay the hardwoods. What do you guys recommend? Thanks again guys for the help.

One half dozen the other. Best bets probably on a diagonal. But a bunch of waste and a PITA. Tough to tell without seeing it. But I'm kinda leaning toward opposite the subfloor to stiffen subfloor flex. But then again..........

Thanks for the help. Here is a rough photo of the floor plan. I hope it comes out somewhat clear.



Any thoughts?

Yea, I 'm not really fond of having a laundry room in the foyer. Should be back behind the kitchen.