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-   -   3/4" T&G plywood over 1/2" subfloor (http://www.diychatroom.com/f19/3-4-t-g-plywood-over-1-2-subfloor-59132/)

Stude 12-12-2009 05:10 PM

3/4" T&G plywood over 1/2" subfloor
 
I have removed the 3/4" particle board subflooring that was installed over
1/2" plywood subflooring. I am going to replace it with 3/4" T&G plywood.
My question concerns the nailing of the 3/4" plywood. Do I fasten it or not fasten it to the floor joist ? I have seen different opinions. I will be using 3/4" strip flooring as the finished floor.

Daniel Holzman 12-12-2009 07:19 PM

I too have been curious about the different opinions on proper installation. From review of manufacturers posted information, I conclude that the underlayment (the lower plywood layer) should be nailed or screwed to the joists using ring shank nails or screws approximately 1 1/2 inches long. Most of the sites I checked state that you should NOT glue the underlayment down, although I am not clear why not.

Most of the sites recommend attaching the second layer of plywood (the upper layer) using nails or screws slightly shorter than the thickness of the plywood, to prevent penetration through the lower layer, that could damage pipes or wiring. They also do not recommend gluing down the upper layer, and they do not recommend nailing into the joists. Presumably the lower layer is already firmly attached, hence there is no need to overkill the project by nailing or screwing the upper layer into a joist.

Joe Carola 12-12-2009 07:49 PM

Quote:

Originally Posted by Stude (Post 365633)
I

My question concerns the nailing of the 3/4" plywood. Do I fasten it or not fasten it to the floor joist ?

You HAVE to nail it to the floor joists. Start at the opposite end so that the joints don't line up. You don't need T&G for the underlayment above a 1/2" subfloor..

paul100 12-12-2009 08:05 PM

On quick question. Why do you have a 1/2" subfloor. I have never seen or heard of that.

Joe Carola 12-12-2009 08:39 PM

Quote:

Originally Posted by paul100 (Post 365721)
On quick question. Why do you have a 1/2" subfloor. I have never seen or heard of that.

I started framing in 1983 all we used was 1/2" subfloor and after that we would go back and install 1/2" underlayment. We stared using 3/4" T&G around 1987.

Gary in WA 12-12-2009 09:18 PM

http://www.apa-europe.org/Languages/.../PDF/R340G.pdf
Be safe, Gary

Gary in WA 12-13-2009 12:10 AM

Daniel, the glue can show through on some resilient flooring products due to the dark color and chemical make-up of the glue----- even 1/4" plywood. With hardwood flooring over, glue is good from APA: http://www.apawood.org/searchResults...ent=srv_search
Free membership, Form R 280.
Be safe, Gary

pyper 12-14-2009 12:50 PM

Isn't there a way you can add to the 1/2" you have? It seems like taking it out is going to be a really big job with a lot of potential downsides.

Gary in WA 12-17-2009 03:59 PM

Quote:

Originally Posted by Stude (Post 365633)
I have removed the 3/4" particle board subflooring that was installed over
1/2" plywood subflooring. I am going to replace it with 3/4" T&G plywood.
My question concerns the nailing of the 3/4" plywood. Do I fasten it or not fasten it to the floor joist ? I have seen different opinions. I will be using 3/4" strip flooring as the finished floor.


Be safe, Gary

drtbk4ever 12-17-2009 04:19 PM

Quote:

Originally Posted by pyper (Post 366576)
Isn't there a way you can add to the 1/2" you have? It seems like taking it out is going to be a really big job with a lot of potential downsides.

I think the OP was stating he was going to replace the 3/4" particle board with 3/4" T&G. He will be leaving the existing 1/2" subfloor.

ccarlisle 12-18-2009 09:39 AM

That's what I read, too. It almost sounds like he's about to tile the floor and If so, then replacing the particle board with T&G plywood is essential.

Plus, if he's tiling, he shouldn't screw the T&G into the joists. So since we don't know what he's going to do (tile, hardwood, VCT etc), none of us is in a real good position to say what to do with the subfloor nor the underlayment.
:no:

pyper 12-18-2009 09:46 AM

Too many pronouns. :laughing:

When he said "1/2" plywood subflooring. I am going to replace it " I thought he was talking about replacing the plywood.

drtbk4ever 12-18-2009 10:38 AM

:laughing:

Further to this, the OP indicated he/she will be laying down 3/4" strip flooring.

:whistling2:

ccarlisle 12-18-2009 12:08 PM

My bad...missed the part obout strip flooring.:laughing:

brenda o 12-26-2009 02:38 AM

I would nail, no glue. Nails should go into joists when possible and be used every 10-12 inches on face of the plywood whether its t7g or not. need to leave expansion room at all edges. reason for the nailing is so that you don't have "creeks" when you walk on it when its finished. I used no t7g plywood under finished product and nailed 4 in in from edges then 6 inched in through the whole sheet. Trick is to nail it down good and tight, no squeaks or creeks later! nails are the flat head with the swirls along the shaft so they don't wiggle out easily for the non t&g plywood. However, with t&g, the common nail could be used so it doesn't split the tongue part. Good luck, I had a lot of help from this site putting in my flooring:) I'm looking for drywall info this morning though:)


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