Adding another layer of subfloor


Old 12-22-15, 04:23 AM
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Join Date: Feb 2006
Location: MI
Posts: 156
Adding another layer of subfloor


I have a family cottage I am attempting to remodel. It has 3/4 plywood over 2x8 joists (16 oc) and over a crawl space. I am going to add another layer of 3/4 plywood over the top a living area that was formerly carpeted, in order to install vinyl laminate throughout the whole home.

My question is....should I install the plywood sheets perpendicular to the current subfloor (90 degrees rotated)? Or should I install them with the length/grain going the same way - just stagger the joints so they don't line up?

Also, the current floor is nailed. I was thinking about going over it with screws, then screwing and gluing the next level of subfloor. This is a high traffic area, and I am just looking to avoid squeaks if possible. Is this overkill? Skip the glue? Or use the glue?

Last tongue and groove necessary for the second layer? Or since there is already a layer of TG, it is entirely necessary.


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Old 12-22-15, 05:28 AM
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Join Date: Jul 2007
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Is 3/4" needed? 1/2" would be fine to give the floor some stiffness. Yes, screw the original floor down, pull any offending nails that currently squeak. Use exterior deck screws for subfloor application. Do not glue the second layer down. The strength axis of the panels says that they should be placed across he floor joists, not running with then. Stagger the joints so they don't line up an screw the second layer to the first, not the joists.
Old 12-22-15, 06:16 AM
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Join Date: Feb 2006
Location: MI
Posts: 156
Great - thank you. I will avoid the glue...and will only screw the thickness of both panels (1.5")

I am adding 3/4 simply because it will make the height the same as the adjoining room. Otherwise I would be happy to add 1/2.

Thanks for the advice
Old 12-22-15, 06:27 AM
Join Date: Jan 2011
Location: USA
Posts: 4,185
Why does it even need a second layer?
What grade of plywood and condition is that subfloor in?
All a vinyl laminate needs is a smooth flat surface so in most cases you could just use 1/4" muti ply subfloor rated plywood and not have to deal with such a big difference in floor heights, no luan!
Only floor that would need all that added thickness is tile.

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