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1/2" Particle board over 1/2" Plywood Subfloor, History and Bathroom Questions,


Civicminded's Avatar
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01-30-16, 04:46 PM   #1  
1/2" Particle board over 1/2" Plywood Subfloor, History and Bathroom Questions,

I have a Site built, stick built house built in 1978 that has sub floors that consist of 1/2 plywood with 1/2 particle board on top of it. I live in Indiana and it seems that this was a common method back in the mid to late 70s. What was the theory behind this? It certainly doesn't seem any stronger than 3/4' plywood and of course if it get wet its junk. Was this something that was done all over or is it an Indiana thing?

Im not sure I would every buy a house with this setup again, I have had to pull up so much particle board and replace it with OSB its not funny.

Now onto my question, I have a bathroom I have completely gutted and I need to lay down 1/2 OSB over the 1/2 plywood subfloor, I have removed all of the particle board in that room. Originally the tub was just set on the 1/2 plywood subfloor, they didn't put the particle board under the tub. Should I put OSB under the tub area or not? Does it even matter?

Thanks

 
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01-30-16, 07:21 PM   #2  
I can't honestly answer your question without knowing what your finish floor will be... since knowing that is critical to the subfloor.

 
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01-31-16, 06:07 AM   #3  
I've seen it done that way many time's.
Have to agree, just made no since.
More often I've 1/2 subfloor then 5/8 or 3/4" over that.
To me all that 1/2" is doing is acting like a shim on top of the joist.
When I find it done that way I remove it all and install 3/4" T & G Advantech subflooring with glue on top of the joist.
Then I have a rock solid non flexing floor that has a 50 year warrenty.

 
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01-31-16, 06:17 AM   #4  
Particle board was a way for manufacturers to utilize the mountains of saw dust and get more mileage out of a tree than before. It produced a completely flat surface that at the time seemed ideal for what most people were installing, which was wall to wall carpeting. Before that it was mostly hardwood. However, the issues with swelling from water, pet urine and such didn't raise its head until people started replacing the carpeting 10 or so years later. I've removed more than my fair share, so in that light, it is good for business - other than that, the stuff is garbage and needs to come out.

As far as your bathroom, if eventually going for tile, I would install 3/4" on top of the 1/2" then your backerboard. Going under the tub is not necessary unless you have ripped everything out already and it is wide open.

 
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01-31-16, 04:09 PM   #5  
I have the whole room gutted so I guess I will put OSB under the tub. I am planning on putting down waterproof laminate, or a sheet of vinyl flooring, definitely not going with ceramic tile, the floor in there is uneven and i am not interested in trying to level it out.

In all the other rooms we have pulled up the carpet and put down laminate flooring and I have had to leave all of the sheets of particle board that were undamaged, not my first choice, but money was an issue. Like I said I will probably never buy another house with this type of sub floor unless the house was really cheap and I was up to gutting it all.

 
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01-31-16, 04:16 PM   #6  
I have never seen particle board used as a subfloor. All I have ever seen was plank, plywood and more recently OSB.

"To me all that 1/2" is doing is acting like a shim on top of the joist."

The 1/2" plywood is mostly a working floor for the framers.

 
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