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We have some old flooring that comes to a total (flooring and planks) of 1 5/8" from the top of the joists. I want to add a new section of flooring (this one) beside it, and am trying to get them to be as close as possible in height.

The planks in the section I am replacing are too far gone to be used, I have to replace them.

So my question is, for this particular floor (or flooring like it) can I combine 1/2" and 3/8" plywood for a total of 7/8" sublfoor? This was I can lay the 3/4" flooring on top and hit the 1 5/8" thickness I am looking for.

Our floor joists are 24" on center, if that helps.

Thanks!

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I don’t think you can glue them together successfully. What about “extreme fiber in bending” and long term creep. Plywood manufacturers use heat and pressure. The neutral axis will remain with the 1-2” plywood.

Id use 3/4” plywood (which is rated for 24” spans) and add 1/8” plywood or moisture barrier to achieve the 7/8” height.

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Structurally, there is nothing wrong with your plan. But I suspect your floor might be prone to squeaking due to having 2 layers of plywood rubbing each other. Gluing them together will prevent the squeaking. But gluing large pieces isn't that practical thus a less reliable option would be putting lots of screws to keep the 2 together.

That being said, don't you want to put an underlayment between the plywood and the new flooring? That serves as a cushion, moisture barrier, and help w/ the sound isolation. Take that in account. It is usually 2-3mm thick.

Would 3/4" plywood plus the pad be close enough to your existing floor?

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  • I love this idea. What underlayment am I looking for specifically? Can I use underlayments intended for laminate flooring such as this?renodepot.com/en/floor-underlay-foam-48-x-25-84665600 – Matthew Goulart Jan 19 at 15:31
  • @MatthewGoulart what sort of intallation are your considering? Nailed, floating, glue? The RenoDepot site doesn’t give much product info to be useful. I would recommend to visit few local flooring stores. They have more selection, usually at lower price, and they can help you find the right pad for you situation. For example some are better for sound proof while others are better for moisture control. The pad I posted is optimized for floating installation. Its smooth surface allows the floor to shift. – Quoc Vu Jan 21 at 18:22
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Yes you can however if you want the equivalent structural capacity you need to glue them together essentially the same as the layers are done in the factory. Just use lots of glue and lots of screws to hold them together so the glue can cure with good contact. The underlayment is a great idea too.

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