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Unread 06-30-2020, 07:49 AM   #1
Levski87
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Subfloor issue in small room

Hello,

I recently purchased my 1970s home and am renovating a 6x8 laundry room. The dilemma I am facing is around the actual subfloor. This room only contains 1/2 inch subfloor and one of the interior walls currently sits on the subfloor entirely, which ironically contains all the water and drain lines within it. The problem I am facing is that there is no joist or blocking that exists underneath that wall, and the subfloor is entirely providing support. I cant open up the ceiling below to put in blocking since tenants currently reside in the apartment below. The joists are 16 OC, and the nearest joist within the room is about 9 inches away from the wall. My idea is to put in 3/4 inch plywood directly over the old subfloor, which is still in good condition, but I obviously wont be able to nail it into a joist towards the end of that wall and wanted to see if my method above would be good enough to contain tile, or should I just go with LVP?

Thanks all.
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Unread 06-30-2020, 08:59 AM   #2
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Welcome, Denis,

Yeah, quite a dilemma. That 1/2" ply is all but useless for anything other than carpet or vinyl. If there really is no blocking from joists to joist supporting that interior wall then there's nothing to support that edge of a second layer of plywood, the 1/2" ply just flexes too much between the joists. And even if there is blocking it would need to be 16" OC.

Not a lot of options since you cannot get to it from below.
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Unread 06-30-2020, 09:25 AM   #3
Levski87
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I've read online that when screwing in the new plywood over old, I should ensure that I dont screw it into the existing joists, which in my case would work out well. Is this a viable method?
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Unread 06-30-2020, 09:40 AM   #4
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Welcome, Denis.

I'd vote for the LVP.

Installing the 3/4" plywood as you plan would require that you do fasten to the joist structure as though the original half-inch subflooring layer were not even present. At the wall where you have no joist you will need to pre-drill the 3/4" sheet and fasten to the existing subfloor as best you can.

You indicate that the original half-inch subfloor is in "good condition." If the surface is in near pristine condition, you could install a second layer of half-inch plywood using a full spread of wood glue and lots of screws into the existing plywood and potentially have a useful subfloor. Tedious work when done correctly, but feasible in your application. But only if that existing subfloor is in nearly new condition.

My opinion; worth price charged.
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Unread 06-30-2020, 05:05 PM   #5
Levski87
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Good to know. If I go with the additional 1/2 inch approach, and then add ditra and tile, will it hold up over the years?
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Unread 06-30-2020, 05:13 PM   #6
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If your existing subfloor is as described above, and if you install the second layer properly as described above, and if your joist structure meets the industry standard for deflection, then yes, I would expect your subfloor to be sufficient for a lasting ceramic tile installation, but you'll not find that subfloor package listed in any industry literature.

See my warranty information below.

My opinion; worth price charged.
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