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?



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. 

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@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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