Screws VS. Nails

christoph

Why do you use one over the other?

carpentermikeal

screws have 300 times more holding power. threads cut into and deform wood to hold tightly. nails grip with friction hold will loosen when wood shrinks and may pop nail head above surface and create callback in a drywall situation.

Grumpy

Summary: screws hold much better. Nails drive much faster.

christoph

I think pretty much the same, just wondering if anyone had anything to add. I also like the idea of using bolts, but time would be a huge issue with that.

Mike Finley

What nobody knows about shear? You better not be using screws when shear forces are a factor!

I know somebody that thought using drywall screws to put his deck together would be a good idea, since screws hold so good right? About a week after it's done he keeps hearing these loud BANGS at night, comes to find out the joists were shearing off! He found out what lag screws were all about in a hurry before his hot tub ended up taking a drop!

- - I would be curious to know if there is really much of a difference between ring shanks and screws when it comes to holding power?

MinConst

I've always considered screws to be far stronger. Mike brings up a good point on shear strength though. Drywall screws are not though of a a quality screw in my mind. Good for drywall and some light weight uses but hold a deck would not be in that thought. Screws don't move if installed properly and can be used to gain a clamping action if drilled properly. In the basement remodel I'm doing now I used screws for most of the framing. Much less noise and driving a screw doesn't tend to damage things on the other side of the wall or floor.
I once heard there was a code or something about using screws and that makes the structure temporary. Anyone ever heard this?
For decks I don't think you can beat the newer screws out. I use Deck mate and have removed them 2-3 years later. Still looked and worked like new.

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Mike Finley

Yep, drywall screws are the worst screws you can use for just about anything - but drywall. All screws suck for shear strength though, I can't even begin to count the amount of screws I have broken off just driving them even into pine 2x4's. Drywall, galvanized, stainless steel, they all such for shear. Don't be putting in your Simpson hangers with screws of any kind, that's a big no-no.

Paul I can't believe you are screwing together framing in a basement remodel! You got patience that's for sure!

mikesewell

Mike,
If you like math and engineering, the answers to many of your questions on this subject can be answered by the National Design Specification put out by the American Wood Council. If you don't enjoy math, then you can always use the empirical approach. Try to pull some screws out with your hammer, and you will quickly have your answer. Generally, nails and rivets are not supposed to be loaded for withdrawal, that's what screws and bolts are for.

Also, don't preload your screws, that's a mistake that most people make.


http://www.awc.org/Standards/nds.html

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MinConst

I should have said, didn't use screws to prebuild the walls. Just to fasten to the joists.

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mikesewell

The Residential Code of New York State has a nailing schedule for structural members. If you check your local code, you may find that you do not have many options when it comes to structual members.

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timntools

I think when it was mentioned above about the shear strength, they hit the nail on the head...so to speak. Screws are awesome for decking, but not for joist hanging. And there is that time/hand fatigue factor...

the best tests were mentioned, try pulling on a screw with a claw hammer, very tough to pull up if at all.

but...try putting both in horizonally, leaving about a half inch exposed, and strike vertically with a hammer. You'll see that the nail may bend but the screw usually breaks off.

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Joe Carola

What are we talking about using screws for?

We certanly don't frame houses with them. The only time we've ever used a screw on a house was for the decking but that's not on every house. Are we talking about framing?

Joe Carola

mikesewell

LOL.
I'm just doing it out of boredom, but I can't speak for the others.

Just joking.

There are lots of screws in most houses; they're a good choice for many applications. If you think about it, you should be able to come up with a long list.

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IHI

If I'm building a structure and need to temproarily hold a joist/beam whatever I'll use a screw or two temporarily until I get my nail gun handy, makes it alot easeir to fine tune adjustiment by backing screw out if need be that taring the wood all to heck pulling a nail.

It's already been said about shear force and that is why nails are the prefered fastener over screws since screws are brittle and snap due to thread taking away from core diameter, core metal and treatment process, whereas nails as just a "thick" or standard diameter peice of cold steel and will bend under load should something bad happen.

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Mike Finley

I looked around that site but couldn't find anything on holding power.

What does "don't preload your screws" mean? What does "nails and rivets are not supposed to be loaded for withdrawl" mean?

Teetorbilt

Mike, I was wondering the same thing and I have dealt with all of them in different applications.
I suppose that you could say that a screw was preloaded due to the fact that it is under some tension under application but this is usually accounted for under working strengths.
The 'loaded for withdrawal' has got me beat.

mikesewell

Teetorbilt,
Correct. When a screw is just barely seated, it can develop it's maximum holding strength. Cranking on it any more than that is preload. Any preload added after the screw is seated takes away from the strength. It puts the screw shank under tensile stress, and puts the screw that much closer to pulling out.

Withdrawal:
Nail a 2x4 to a stud, hang a weight from it. The load puts a shear stress on the nails. Nails work very well for this application.

Nail a 2x4 up to a ceiling joist, hang a weight from it. The load puts a "withdrawal" (tensile) stress on the nails. A screw works much better for this application.

Mike,
Sorry; you can look on that site all you want, but it won't tell you $#!t. You have to order the books (capitalists). When it comes to wood, the National Design Specification for Wood Construction is THE standard for rational design.

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Mike Finley

Thanks for the explanations, they all make good sense!

Teetorbilt

Yea, thanks.
BTW, I have a B.E. and an M.E. 'Withdrawal' was new to me, tensile strengths I understand.
This site should end any and all questions on this subject http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm

Teetorbilt

aka retention failure, which is the subject in this comparison.
I almost launched into a dissertation, but, in a nutshell, when comparing nails to screws, screws will prevail in every instance.