# Installing plywood underlayment



## acglobal (Feb 7, 2011)

you have hit everything on the head correctly. As far as nailing/screwing into the joists, I'll let one of the tech. guys answer. Personally I dont screw plywood underlayment through sheathing into joists unless 1) there are squeaks or 2) I am installing tile.


----------



## JazMan (Feb 17, 2007)

Hi Ben,

A tile installation requires the most critically stiffest subfloor/underlayment system. I don't see why we should lower the standards for other types of flooring.

Re-fasten the sub to the joists. Fasten the underlayment to the subfloor only using 1 1/4" flooring screws. In this case shorter screws will be OK since the sub is only 5/8". 

Ply always goes across the joists regardless on the installation. Offset by at least 20-22" if possible. The accepted gap between sheets is 1/8". 1/4" at the perimeter and solid objects. 

NO GLUE. Unless it's a thin wood glue and you can spread it 100% to laminate the two. 



> There is so much conflicting info out there. Some say DO NOT screw all the way to joists and some say DO hit joists where possible.


If you use the right screws you will not hit the joists when installing the underlayment. 

Jaz

PS.


> Personally I dont screw plywood underlayment through sheathing into joists unless 1) there are squeaks or 2) I am installing tile.


Sorry, this is wrong.


----------



## Gary in WA (Mar 11, 2009)

Yep; http://www.apa-europe.org/Languages/English/PDF/R340G.pdf

Gary


----------



## benr (Jan 20, 2011)

JazMan said:


> Hi Ben,
> 
> A tile installation requires the most critically stiffest subfloor/underlayment system. I don't see why we should lower the standards for other types of flooring.
> 
> ...


 
Thanks for the advise. Why No glue?, will it make the surface uneven if not spead properley?


----------



## JazMan (Feb 17, 2007)

> Why No glue?, will it make the surface uneven if not spead properley?


Absolutely, go to the head of the class. Most people would use a thick construction glue from a tube. These beads create slight hills there fore creating tiny valleys, therefore voids. Some people can't get it in their heads that it is not good to glue underlayment. The subfloor YES, cuz you're gluing to the joists, big difference.

Jaz


----------



## kirm (May 1, 2013)

*I'm doing this exact thing*

I just joined to give a big thanks to the Jazman. I've been researching this for weeks and have run into his posts a few times. They're always right on the money.

Thanks Jaz, you've been a huge help to me in my home projects.


----------



## sam floor (Jun 27, 2009)

And don't use drywall screws. Use galvanized screws or deck screws.


----------



## JazMan (Feb 17, 2007)

Kirm,

You said;


Kirm said:


> I just joined to give a big thanks to the Jazman.


Very nice of you to stop and say that, but stick around. :thumbsup:

Jaz


----------



## Even Further (Dec 7, 2012)

Check out these GRK R4 screws. I use these GRK's for many different projects, and come in handy.

http://www.amazon.com/s/ref=nb_sb_n...eld-keywords=grk+screws&rh=i:aps,k:grk+screws


----------



## pcondon (Mar 4, 2014)

At the advice of a local contractor--I glued AND nailed the underlayment into the joists. Surprised he told me this when I found the opposite info online, as he's been doing it a long time. Guess he uses the old train of thought. 

Anyways, doing 3/4 unfinished hardwoods on top. Will I be ok or is my house going to crumble to the ground? (that's a joke)


----------



## JazMan (Feb 17, 2007)

That's an instinctive way to install underlayment, it's just not the recommended way. I don't know about "old train" and this error should not be a major disaster. 

There's "pros" out there that have been doing some things the wrong way, for "30 years, and have never had a problem". In short, how long one has been doing things wrong is not a plus. But again, not a big deal in this case. 

Jaz


----------

