Have questions, need tips on new subfloor


Old 05-04-09, 12:05 PM
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Join Date: Apr 2006
Posts: 3
Have questions, need tips on new subfloor


We are currently in the process of planning a living room renovation. We pulled up the carpet, pad and first layer of subfloor this weekend to check the condition of the hardwood underneath. Unfortunately, the existing hardwood is in pretty bad shape, so we’re looking at installing new hardwood ourselves and I had a couple questions about prepping a new subfloor.

While the floor (or the house for that matter) itself is not exactly level, it is (for the most part) flat. However on one side of the room, there is a rather sever drop off (about 3 quarter inch over a 4 foot span). When pulling up the subfloor, we found that the previous owners had placed a series of 1x3s cut to various thicknesses to shim up the low side prior to laying the subfloor. We figured that we would do basically the same thing. Is this the best/easiest approach to flattening the floor?

Can we install new subfloor directly over the existing hardwood? Or is there something we should lay between the old hardwood and the new subfloor?

Also, what type of wood should we use as the subfloor and what thickness? I have seen people mention plywood, OSB and Advantech (I think that is what it is called), is it just a matter of personal preference and cost or do any of these have specific advantages over the other? Should I go with half inch or 3 quarter inch? Tongue and groove?

I should probably mention that the floor itself is over a basement that gets damp from time to time in heavier rain. We have a dehumidifier that we run whenever that happens, so I think that moisture is only a minor concern, if any concern at all.

Thanks in advance for any tips!
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Old 05-04-09, 05:45 PM
Join Date: Mar 2009
Location: WA
Posts: 1,167
What is your joist spacing? How many layers are there, of what?Is the basement ceiling insulated? With a vapor barrier? Be safe, G
Old 05-05-09, 04:44 AM
Join Date: Jun 2008
Location: Southeast, Pa
Posts: 358
Why not remove the old flooring and install the new hardwood on existing sub-floor? Use tarpaper on top of sub-floor prior to installing hardwood. If there is a low spot you can shim as was done before. I would not go over the old hardwood because it would make the floor too high.

Old 05-05-09, 08:33 AM
Thread Starter
Join Date: Apr 2006
Posts: 3

The joists are 18 inches on center, made of 2x7s (strange, but those are the actual measurements). We now have two layers. The first of which is 1" thick planks varying between 6 and 8 inches wide perpendicular to the joists (not sure what kind of wood), then a layer of what appears to be 3/4 hard pine floor (about 3 1/4 wide). The floor is pretty solid, not a lot of bounce. Basement ceiling is not insulated, but we're deciding whether we should or not.

Bill62 –

The thing is the existing pine is relatively flat, except for the large dip in that one area and we do not know what the condition of the subfloor under that is. I am not sure what can of worms we would be opening up if we removed the existing hardwood, so we figured building on top would be the easiest thing to do. Also, since we already removed one layer of 3/4 particle board, linoleum, pad and carpet, we’re confident that building on top of the existing hardwood would only raise the level of the floor to what it was before we started, maybe even sit a touch lower. As it stands, the living room floor is now about 2.5 inches lower than the kitchen floor. Figure adding 1/2 or 3/4 of new subfloor, plus 3/4 new hardwood wouldn’t make much difference.

Thanks, guys. I appreciate the help.

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