What would you do - 5/8Ē diagonal T&G subfloor

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Old 08-24-19, 05:12 AM
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What would you do - 3/4Ē diagonal T&G subfloor

Iíve spent many hours researching and canít seem to find a consensus. Iím hoping you pros can help.

Iíll be installing 3/4 solid oak, 4Ē wide, Mullican floor.

My basement is currently unfinished and I run a dehumidifier in the summer. I live in the north east.

My subfloor is 3/4 inch t/g, run diagonal over 16Ē oc floor joists. In ok shape, some soft spots and places where the t&g is no longer together.

I plan to screw the existing sub floor down to the joists and block any soft spots from below.

I want to add plywood over top for a little added strength but canít go too thick because I need to meet up with 3 different sets of stairs. 1/4 or 3/8 max.

I have 2 questions. Would you install the plywood and if so how would you secure it? Staple, screw or nail? Glue or no glue?

For the floor install I was planning to nail with glue assist. Glue in a serpentine pattern. Is this a bad idea given the summer humidity?

Thanks for looking and Iím hoping you can help this lost cause. I canít seem to pull the trigger on an install plan yet.
 

Last edited by cantDecide; 08-24-19 at 06:20 AM. Reason: Wrong sub floor thickness given
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Old 08-24-19, 05:28 AM
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Unusual that it would be 5/8". You sure about that?

Your flooring instructions have subfloor guidelines, so follow them. But if is really 5/8 I would probably add 3/8 of that's the most you are willing to do. Screws on 12" centers, nothing into joists, no glue. Over that you want felt or rosin paper, and your floor is nail only. I like starting out in the middle of the floor by gluing a spline into the groove of a plank... then work in both directions away from that point. Less total expansion and contraction.
 
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Old 08-24-19, 06:06 AM
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First off. Thank you very much for your time and your reply. I appreciate it very much.

You are correct it is 3/4” inch!

My thought process on adding something over the existing subfloor was to add a little extra support. I realize 1/4 isn’t structural, but when screwed down it should tie everything together a bit. No?

The glue assist option for the flooring is noted in the install instructions and it seems like a 50/50 recommendation for a 4” wide board.

“Option: to reduce movement add a serpentine bead of high quality urethane adhesive to subfloor as well as mechanical fasteners. This will require the moisture inhibiting paper NOT to be used. (Example of adhesive- Liquid Nail or Lockedtite: urethane wood to wood adhesive.)”
 
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Old 08-24-19, 08:09 AM
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Based on the feedback and a little more research I think I'll do the following.

- Secure existing sub floor with screws
- Block any really soft spots from below
- Vapor barrier over existing sub floor
- Screw down 1/4 plywood with 3/4 screws so they don't poke, I'm concerned about adding too much height
- Flooring installed with glues assist. Will use a serpentine pattern on the back of each board.

Flame away. Thanks for looking!
 
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Old 08-24-19, 10:17 AM
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Yeah, I still wouldn't use glue.
 
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Old 08-24-19, 01:38 PM
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My subfloor is 3/4 inch t/g, run diagonal over 16” oc floor joists. In ok shape, some soft spots and places where the t&g is no longer together.
3/4 what?

Unless it;s something odd you have a sufficient base for new floors. Don't need to add anything but fix any areas needing attention.

New floor will be installed per manufacturer, either nail (my recommendation) or glue, not both!

Vapor barrier over existing sub floor
No vapor barrier, why are you suggesting!
 
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Old 08-25-19, 01:47 AM
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Thanks again for the input. It’s very much appreciated.

The subfloor is 3/4” t&g plank. It’s in ok shape. There are some spots where it shrank and the tongue is no longer in the groove. Some spots feel softer than other when you walk on it.

I did did read the manufactures instructions and they do mention the glue assist. So I thought it could help.

I think maybe I misspoke about the “vapor barrier”. I meant more the moisture retarder. It is also mentioned in the instructions. 15# felt, SVP, Aquabar b.

Thanks again. I know I’m making this more complicated than it needs to be.
 
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