Flooring / Subfloor

8 Replies

I am renovating a house in Philadelphia. I have old growth pine tongue and groove 'subfloor' on top of the flooring joists (3/4" thick). I then have a 1/4" thick layer of what appears to be MDF or possible masonite. I want to add another layer of subfloor to strengthen the floor after patching in certain areas. Note: I put new beams in the basement to support the floor joists at the midpoints (it's an old house).

I have access to a lot of OSB sheathing 7/16" for free and was wondering if that will hold up well if I put hardwood flooring on top of it. Typically, I wouldn't put OSB down but given that the T&G pine is underneath it all I don't see it as an issue. 

Can anyone advise whether I will see issues with using the OSB?

Thanks,

Sean

Im not quite understanding why you want to add more flooring? You already have 1" of flooring down. What are you trying to strengthen exactly?

I'm leveling the floors. This house was built in 1860. I jacked the house up as far as I wanted to take it (hence the new beams) and now I want to add some additional subfloor to add some stability and level it out a bit more. 

If you are looking for stability, I wouldn't use OSB, use plywood.  There's a reason why you never see OSB for subflooring and only for sheathing.

^ Well, actually OSB is used more than ply for sub-flooring.

@Sean Pincus  

I personally do not see a problem with using osb.  would plywood be a better option? yes, but I see osb used  for roof sheathing as well as on exterior walls of new construction all the time.  when I have replaced subfloor in the past I use nails instead of screws, and I use construction adhesive on the new subfloor.  hope this helps.

adam drummond

I doubt that 7/16" OSB will get you the added strength/ rigidity you are looking for. 3/4" T+G pine would be better especially if you are trying to level the floor and need to shim between the layers.

I wound up using 3/8" plywood... Glue and screwed to the existing subfloor. It'll then get 3/4" hardwood over a vapor barrier. It came out really nice. Cost me a couple bucks but at least I won't think about it daily and let it ruin my sleep.

Thanks for the replies! 

To say ply is better than OSB -- or vice versa -- doesn't really mean a whole lot.  There are so many variations on the specs of each that you'd really have to do a bit of homework beyond the generic names.  Many types of OSB outperform many types of ply.  Neither type likes water.  Building codes generally interchange the two for sheathing / sub flooring. Always check the warranty requirements of your finished floor material as it relates to subfloor performance requirements.

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