Looking for guidance installing hardwood floors for the first time...

[Mustard Tiger]

Pulled out the old carpet and padding to discover particle board underneath (place had wall-to-wall carpet everywhere including one of the bathrooms). The particle board sits on top of a 1.5" T&G subfloor. After I go through and remedy any loose or squeaky boars in the T&G subfloor the plan is to get rid of the garbage particle board and replace it with T&G plywood and prep the floor for hardwood, ensuring it's flat, mitigate deflection, etc. Plywood is lighter and offers more structural integrity

First issue I've encountered is the particle board was installed before the T&G cedar walls. How do I get the particle board out from under the walls, or should I just use a toe kick saw and cut it flush to the wall and not worry about removing it all underneath the planks on the walls since I'm obviously not going to be installing the hardwood flush with the walls anyway, and the gap will be covered by moulding.

The next issue is with the current particle board I am noticing some deflection in the floor. Hoping this could jsut be the particle board, but if it is the subfloor and laying down the plywood doesn't help, I'm kind of screwed. The thing is that 1.5" T&G subfloor is also the exposed ceiling in the rooms below it. No drop ceiling, sheetrock, etc. The subfloor is also the exposed ceiling, so can't really add any bridging underneath because it would kill the aesthetic. Joists are also pretty far apart.

If I am still getting deflection and can't add bridging because of aesthetics to the ceiling below, should I avoid installing solid hardwood and go with a different type of flooring? Here's a picture of the ceiling in a bedroom which shows the subfloor for the loft above (those curtains are from the previous owner).

Here's a few shots of the place with the carpet and padding removed and particle board exposed:

Loft:

 

[highup]

The particle board is 1/2 Inch?
That why you're getting deflection. Over time, the movement of the particle board will further weaken it.
I wouldn't be concerned about leaving particle board under the walls or railing.

 

[highup]

After removing the particle board, I'd add screws from the T&G into those beams. Stiffening the floor with plywood might cause annoying squeaks if to don't.

 

[C.J.]

Taking the particle board out from under the walls is just asking for trouble. Toe kick saw and a multi tool will get you flush to the walls for removal of the particle board.

Do you even need to go back with plywood after removing the PB?

 

[highup]

Taking the particle board out from under the walls is just asking for trouble. Toe kick saw and a multi tool will get you flush to the walls for removal of the particle board.

Do you even need to go back with plywood after removing the PB?

 

[C.J.]

The particle board was installed before the walls were built which is why it is underneath the walls. You’ll have to literally dig it out, the walls will sink that 1/2” cus you’ll never be able to get em back up to slide plywood back underneath them. Even if you were that good, you’re gonna have to figure out how to resection the walls because you’re gonna be cutting the nails that hold the walls in place in order to remove the PB.

 

[C.J.]

Hard to tell from my phone but is that plywood that is currently down, not PB?

 

[Mustard Tiger]

Hard to tell from my phone but is that plywood that is currently down, not PB?

No, it’s particle board.

 

[Mustard Tiger]

So the general consensus is toe kick around the walls and then lay down new plywood?

Given that the T&G subfloor is 1.5” thick, could I just put down 1/2” plywood over it instead of 3/4”?

 

[Mustard Tiger]

After removing the particle board, I'd add screws from the T&G into those beams. Stiffening the floor with plywood might cause annoying squeaks if to don't.

Absolutely. That's the plan. I know the construction of that floor and the beams is anything but normal. This beams are far apart but huge, so I'm sure there's going to be some about of deflation that you can't really do much about. But with the 1.5" T&G subfloor, then plywood on top and a hardwood floor on top of that. I'm sure it will be much stiffer and stronger than it was with particle board and carpet.

 

[Mustard Tiger]

The particle board is 1/2 Inch?
That why you're getting deflection. Over time, the movement of the particle board will further weaken it.
I wouldn't be concerned about leaving particle board under the walls or railing.

The particle board was installed before the walls were built which is why it is underneath the walls. You’ll have to literally dig it out, the walls will sink that 1/2” cus you’ll never be able to get em back up to slide plywood back underneath them. Even if you were that good, you’re gonna have to figure out how to resection the walls because you’re gonna be cutting the nails that hold the walls in place in order to remove the PB.

Sorry if I didn't explain it accurately. The actual framing of the walls isn't on top of the particle board. You have the framed walls, then the T&G plank on top of the framed walls. Looks like what was done was they framed the house, then put down the particle board, then installed the T&G planks on the walls. So the particle board doesn't have anything "structural" sitting on top of it. But it is tough to get at in a few spots in the loft, especially where the roof line comes down and meets the floor. Even if I can pull out the particle board under some of those spots, I'm thinking just use a toe kick saw around the perimeter and an oscillating tool where the roof like meets the floor in the loft and do the best I can and leave that particle board under the the spots I can't get to easily. That stuff has been there 42 years and isn't wet or swollen/warped. The house is in fantastic shape aside from the crappy particle board Everything else in the house is cedar, the walls, the ceiling, beams, siding on the outside of the house, etc.

I'm wondering since the sub floor is so thick (1.5") and I'll be using 3/4" solid hardwood for the floor, can I get away with just adding 1/2" plywood over top the subfloor or is 5/8" the minimum I can get away with?