Install hardwood on top of a old plywood subfloor


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Old 05-14-20, 10:33 PM
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Install hardwood on top of a old plywood subfloor

I have a old house. After take out all the old hardwood floor, we found the subfloor is thin 5/8" plywood subfloor above the crawlspace( no insulation) . the plywood wood piece has big gap between each piece. I can see through the crawlspace. Some wood piece have big or small hole, like quarter size .
We need to have 3/4" oak hardwood floors installed over this plywood subfloor. what kind of preparation I need do before install ( nail down)?

My concern is the moisture, bug or mice can get through the gap. Do I need to seal the gap and hole before put the underlayment? Do I need to add a layer of pressure-treated plywood on top of the subfloor first? or cork?
Any suggestion? Thanks.
 
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Old 05-14-20, 11:48 PM
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Your flooring manufacturer will provide min recommendations, that would take precedence over any comment provided here.

Typ sub floor needs to be solid and secure 3/4" OSB or plywood.

As far as mice and non insulated area, that probably needs to be resolved and not necessarily just because of he flooring!
 
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Old 05-15-20, 04:39 AM
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#1, Never used pressure treated for underlayment!
The best way, but a lot more work and would not change the height much and the floors will be less likely to squeak would be to remove what's there and install Advantech T&G subflooring.
The second best way would be to just go over it with underlayment rate 1/2" plywood making sure the seams do not line up with the seams below, and fastening every 4" on the outside edges and from 6 to *8" in the field, making sure to never nail into the joist below.
Never use any glue between the layers!
The fastest way to nail it down would be with a pneumatic narrow crown staple gun.
 
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Old 05-15-20, 05:11 AM
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I went through a similar problem two weeks ago. After the fire I ended up with a builders subfloor (1/2" plywood) that was in very rough shape mostly from water damage. Seams were "soft" in places and the subfloor squeaked. We blocked all the seams from below and added a layer of 5/8" plywood on top of the original subfloor. This was the recommendation of the flooring installer. He then added a 15# felt layer between the new underlayment and the hardwood plank.
 
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Old 05-15-20, 05:11 AM
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I would add a minimum of 3/8 cdx on top of the subfloor, screwed to the 5/8 plywood with 1 1/4" deck screws 8" on center. Then felt paper, then you are ready for flooring.

As for the crawlspace, at a minimum your floor should be insulated, and it would be wise to have the crawlspace encapsulated with a heavy poly vapor barrier. Then it should either be vented or conditioned. You don't want moisture from the crawlspace ruining your new wood floor.
 
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Old 05-15-20, 12:42 PM
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Thanks for the suggestion! very helpful!
 
 

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