OSB Subfloor

Rick Jones · February 16, 2009, 08:28 AM

I plan to install a solid, plank (3" or 3 1/4") floor across the joists on the first floor of a 23 year old house. About half of the first floor has/had a solid, strip, nailed floor. I have removed some and plan to remove the rest (wife prefers plank, different species, and different stain).

The subfloor is 3/4" OSB. From what I have read, it sounds like 3/4" OSB is acceptable, but the bare minimum. This concerns me, particularly when several rooms have already had one nail-down.

Would it be better to add a plywood underlayment? If so, any particular type or thickness?

Thanks

Peter Kodner · February 16, 2009, 09:34 AM

Rick, 3 1/4 is still strip flooring. Anything wider is called plank. Not knowing how well the original was nailed, hard to give solid advice. Going with a wider strip, you will have your fasteners falling in different location for the most part so I can imagine only a few will randomly be in the same locations as the originals.

What is your joist system? What species are you considering for the new flooring? Some species have some quirks you should be aware of before installing. Last, where do you plan on purchasing the floor? Not all suppliers are equal either...

Steve Olson · February 16, 2009, 05:46 PM

From my experience, OSB subfloors make for a squeekier install then any plywood. Without knowing how the added height would effect existing thresh holds or other areas where height clearance might be an issue, I would install 3/8" Plywood, over the OSB, then install the wood.
If you don't have the clearance, I would take the time to sand out the joints, and damaged areas, from the fasteners of the previous floor. Then use 15 lb felt over the OSB, before installing the new floor.

I will add, prepping the floor as mentioned above should be done before installing any under layment you might use.

Floorguy · February 16, 2009, 06:41 PM

OSB... Use staples not cleats for better holding power in that beaver barf.

Rick Jones · February 16, 2009, 06:58 PM

Thank you for the helpful input.

Peter - The joists are 16" apart. We are currently considering maple. Like the look and the hardness, but a bit concerned about the potential for movement. Haven't settled on a brand or supplier. Like Mirage, but don't know if its really worth the premium pricing. Any thoughts would be greatly appreciated.

SK - Just as you said, our current wood floor over the OSB has its fair share of squeaks. Do you think the 3/8" plywood would provide for a more stable floor, or mainly reduce squeaking?

Kman · February 16, 2009, 07:09 PM

Sometimes the squeaking can be eliminated with the use of 15lb. roofing felt underneath the flooring. This is not to say yours doesn't already have it, but if it doesn't, that could be the cause of the squeaking you hear.

Steve Olson · February 16, 2009, 07:48 PM

I know from my experience, that wood floors over OSB, make more noise then those installed over plywood. Not knowing what your joist spacing is, or, until you mentioned it, that your current hardwood floor squeaks, a layer of at least 3/8 would go a long way in helping quiet the floor.
But, with diligent prep, on you exisiting OSB you could most likely get decent results with just the prep, 15lb felt, and staples, as mentioned by Floorguy. I would also toss in gluing of the endjoints, for extra bullet proofing. Use a bead of yellow carpenters glue; wipe any oosing up with a damp rag.

Maple is not the most dimensional stable wood, if the maple you are looking at is mixed with light and dark wood, you might be happier with Hickory. If the light color of the premium grade is more your style, maybe take a look at an Ash floor.

Kman · February 16, 2009, 08:18 PM

Hard to go wrong with Hickory. I installed a bunch of it (2 1/4" wide) about a year ago. Hardest wood I worked with, ruined a new blade on that job. But it turned out great.

Solid Pre-finished Hickory Hardwood in a Missouri Home | Welcome to Trevathan Floorcovering

Rick Jones · February 17, 2009, 06:52 PM

So, if I follow, it sounds like it should be ok to lay the hardwood over the OSB using staples, without adding underlayment.

One question about the 15lb. felt. Many posts on this forum seem to highly recommend Aquabar as a vapor barrier. Is the 15lb. felt a better solution with my OSB?

By the way, when I took up my old floor, no barrier was installed between the hardwood and the subfloor.

Steve Olson · February 17, 2009, 07:36 PM

Aquabar is a better in the capacity of providing control of moisture vapor emissions then 15 lb felt. But 15 lb felt is better at suppressing squeaks, though not as effective in the control of MVE.
But, one thing not yet mentioned is that if you were to read through the instruction sheet for the wood you are installing, it should mention the covering of your dirt crawl space, with 8 mil plastic. If you have "heated space" under the area getting the new wood floor, your OK.