underlayment

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I'm installing 5/8' underlayment over a 1/2" subfloor. I've seen contradicting info on how to orient the underlayment. Some say right angles to the subfloor, but some say right angles to the joists. I cant have it both ways, since my subfloor was installed at right angles to the joists. What to do? My previous underlayment (which I removed) was laid across the joists so unless I can find a compelling reason I guess I'll redo it that way.
Also, I want to use nails. Screws are just plain out of the question, and I dont want the expense of renting or buying staple equipment. But the shortest ring shank underlayment nails are 1 1/4", which means every one will be punching a hole and splintering out the bottom of my subfloor, which is not desirable. I know they make 25 mm (1 inch) underlayment nails but I cant find them in the US (or Canada, so far)..
What to do?
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wrote:

How long will a 1 inch nail hold a 5/8" material?
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1 x 5/8 x 12mo = 7.5 months.
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I'd guess about exactly as long a 1 1/4 inch nail that chips out 1/8" of the 1/2" subfloor.
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wrote:

I'm sorry as I'm not certain what you mean by "chips out".
Dangling attic roofing nails can get your suspenders caught on the nail or a hole-in-the-head. Those nails splinter the wood.
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wrote:

Sorry, I cannot accept that.
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First of all I don't consider 5/8" over 1/2" to be under-layment at all. That is called a floor. Half inch is nothing.
Under-layment is something you put down to provide a smooth clean surface for tile or vinyl and can be run either way. Usually it 1/4" and added to at least a 3/4" sub-floor.
I would install it with the 8' running across the joist and try my darnest to hit the joists. I would stagger the seams so that the new does not line up with the old on either direction. I would use a minimum of 8D sinkers to secure it. Now you have a floor.
To minimize potential squeaks I would use a single layer of 30# felt or a double layer of 15# felt. Alternately you can use liquid nails or the like in lieu of the felt.
--
Colbyt
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-snip-

What he said. Though he didn't make clear that all those 8D nails go into joists.
*THEN* you put your 1/4 subfloor in if you need it and use the short ring nails.
Jim
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I already have a subfloor. The subfloor goes on the joists. Underlayment goes on top of the subfloor.
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wrote:
-snip-

Brainfart- sorry. I meant underlayment. I don't consider 1/2 ply to be anything more than a waste of time. 5/8, maybe-- but I wouldn't do less than a couple layers of 3/4. I'd even prefer shiplap for that first layer over the joists. Then 3/4 T&G to smooth things out.
Jim
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Squeaks come from the wood sliding against the nails, not from the underlayment sliding against the subfloor.

Thanks for the definitions. He used the wrong word, so stop being a smartass and learn something.
"Screws are just plain out of the question"...? Why? It's a superior installation, doesn't cost a hell of a lot more, and unless you're doing an entire house won't take all that much more time. Even if you are doing a whole house, the superior installation is worth the time and money. Rent an autofeed screwgun if you're worried about the time.
If you are going to use nails, you should know what nails do, and how they are supposed to work. Underlayment nails, and roofing nails, are designed to penetrate completely through the wood sheathing. They hold much better that way and are far less likely to back out over time. If you are concerned about the appearance from below (you like the look of exposed 1/2" CDX???), then you should look into nailing just at the joists, glue the underlayment down and weight it so there are no gaps between the two layers.
R
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I wasnt being a smartass. It seemed he was suggesting that I install a 3rd layer. I already have a subfloor. He agreed with the other poster that I should install my 5/8 across the joists, and then suggested I install a 1/4 inch on top of that. Nobody suggested taking out the 1/2 inch subfloor, which is good because I have no intention of doing so. But I certainly dont need 3 layers.

Because after reading about the pros and cons I decided I'm not using screws. I might shoot one in here and there if necessary.
It's a superior

I have read the exact opposite. They should not penetrate the subfloor. That was posted above and I have read it in other places. I have also read the opposite, but since nails penetrating the subfloor will splinter (or chip) the bottom and reduce holding power it seems wise to me not to penetrate it completely if possible. I may not have a choice though, if I use 5/8 plywood and nails.
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You're dicking around with trying to improve something that is substandard. Don't. Bite the bullet and just put down a 3/4" subfloor on top of what you've got, then it doesn't matter what you've got and you don't have to worry about attaching the layers. The price difference is small and the savings in not having to mess around with underlayment nails and worrying about attaching two layers is obviously worth it.

Cons? Okay, other than a worthwhile bump up in cost, and taking a bit more time, name the cons.

Yeah, you read. There's a lot of bad information out there, and you went and got yourself some. Attaching underlayment is essentially the same as attaching roof shingles, and the nails are intended to perform similarly. Plywood does not have the nail holding power that solid sawn lumber does. If you had an old-school shiplapped subfloor, 3/4" to 7/8" thick, then the underlayment nail doesn't have to penetrate fully. You don't, so they do.
SBC further specifies that fasteners for asphalt shingles be "minimum 12- gauge (0.105-inch [2.67-mm]) shank with minimum %-inch [10-mm] di- ameter head, of a length to penetrate through the roofing materials and a minimum of % inch (19 mm) into the roof sheathing. Where the roof sheath- ing is less than % inch (19 mm) thick, the nails shall penetrate through the sheathing."
R
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On Thu, 15 Oct 2009 11:30:20 -0700 (PDT), RicodJour

LOL!
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Joe you came here asking for advice and you are getting some from people who really have done this a few times.
Allow me to define some terms. A sub-floor is anything that is not finishable. No matter how many layers of plywood you put down it is all subfloor. Half inch plwood is not a suitable surface to nail or screw anything to if you want it to last. You need to hit the joists with your 8D nails. You are wasting you time worring about stuff that isn't going to last no matter what you do or don't.
You might very well need 3 layers if you plan on using vinyl tile or sheet goods because unsanded (very smooth) plywood is not an acceptable base for either.
You can carpet over the sub-floor as defined above. You might get away with the new loose-lay vinyl over a tightly fitted top layer of smooth plywood.
I have a 3/4" T&G plywood sub-floor with 16" OC joists in a 1995 house. Most of the downstairs has 3/4" hardwood over that. Every darn hardwood nail that did not hit a joist penetrated the subfloor.
Roofing nails are meant to penetrate the deck by at least 1/8" (per mfg instructions).
Good luck with your project.
Colbyt
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And I appreciate the advice. Nobody asked what my finish floor was going to be but I already knew, and that might have avoided some misunderstanding.

I didnt realize it but It appears that they only nailed the previous 5/8 into the joists-I didnt pay that close attention when I pulled it up (it was particle board that had gotten wet, and it was a nightmare), but I see now they didnt nail it in the field much, if at all.

Thats what i'm putting down, floating vinyl in one room and carpet in the other. So it seems I dont have a problem anymore, I just nail into the joists.

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Right, copy the failed installation. Seems like a plan.
R
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Failed? What failed?
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Thats what i'm putting down, floating vinyl in one room and carpet in the other. So it seems I dont have a problem anymore, I just nail into the joists.
Just remember to stagger all the joints in both directions. That might think you think a bit. :)
And as long as you are not using particle board (which you aren't) you are not following the failed installation.
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Perhaps you like unnecessary flexure in a floor, but can you really countenance omitting a simple step that would improve the installation? Instead of having the two layers bonded and acting as one, you'd prefer to save on a few pounds of screws or nails?
R
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