Nails vs Screws

[VannL]

I want to make sure my house is strong. I have heard that using screws is the strongest possible construction method, but no one builds a house from screws.

Am I wrong in wanting to use screws?

[Ernest T. Bass]

Screws don't have nearly the shear strength as nails. Also, they usually fail with a sudden snap, where nails will bend and/or pull out slowly. Much better to see a leaning wall and have time to get out from underneath than have it suddenly fall on you.

Screws have there place when it comes to resisting pull-out, and can sometimes be used effectively along with nails, but not many people bother with the extra time. It takes two seconds to shoot a couple nails at opposing angles next to each other, and as a pair they will resist pull-out quite well.

[rick91351]

I second the Honorable Mr Bass.  However John did have an article on earthquake screw nails on the CountryPlans Site.  I have not noticed it as of late you might drop him an e-mail and see if it is still available.  Very interesting article.

[CjAl]

use the recomended amount of nails and then add some extra screws. thats how i do it anyways

[VannL]

Gentlemen, my thanks. It certainly gives me something to think about. I was not aware that the sheer point of screws was lower than nails. But, I know that screws pull the pieces of wood tighter together than nails can. So, I think I'm leaning toward...CjAl's idea.

[Squirl]

Great summary and explanation by Earnest T. Bass.

Because of those reasons, the building code requires nails.  Many building inspectors will fail framing if it does not have the required nailing.

I would only favor screws where I needed a lot of pull strength and it wasn't structurally dependent such as siding and roofing.

[flyingvan]

Screws won't make a house stronger, just stiffer.  Compare an oak branch to a reed grass in a wind storm---which is more likely to break?  Nails are more ductile--like others have pointed out, they flex a bit.  A house that can move a little can withstand more freeze/thaw, wind, earthquake, etc.

[JRR]

For any given nail, I suspect a stronger screw can be found.  If screws are inherently weaker ... why the sudden popularity of timber-screws?  There are lag-bolts used in wooden bridge construction, nails or spikes could be used...but could the framework endure the pounding required to insert the spikes?  That's a big advantage for screws, they are installed with less impact on the structure.

Does anyone use nails for decks?  Nails are easier to manufacture than screws ... especially strong screws.  I believe screws have a future in home construction .... especially when the latest wind resistive codes adopted by the state of Florida show screws, or nails, used to attach sheathing to framing.  (Or I misread it!)

[Erin]

The reason screws are used for decks goes back to what was said about pull strength vs. sheer.
There's no sheer stress on decking, only pull.  Consequently, screws are ideal for that application. 

I'm guessing that if FL adopted a wind code that requires screws, it's probably in addition to nails, and is in the planes that are susceptible to a direct "pull" from wind... 

Otherwise, nails are better in most applications because as mentioned, they have some flex whereas screws just snap.

[alex trent]

For any given nail, I suspect a stronger screw can be found. 

LLikely you are right, just need to go bigger..so the operative word here is same size.

If screws are inherently weaker ... why the sudden popularity of timber-screws? 

Uhh...there are a lot of thing that have sudden popularity that are not popular because better. So I guess the operative word here is popular with whom.


There are lag-bolts used in wooden bridge construction, nails or spikes could be used...but could the framework endure the pounding required to insert the spikes? 

You are right again, but as is admitted by all but the moat rabid nail fanatic...there are certainly some users that screws are better for.  Does not make them better for other things, such as framing.

That's a big advantage for screws, they are installed with less impact on the structure.

You are kidding, right?  If you building cannot take the pounding of a nail that is proportionate in size to the building, you are in big trouble that even screws cannot help

Does anyone use nails for decks? 

Yes and works fine.  Why not?  Just because you have a power driver does not meant you have to use it.

[Don_P]

Sheer is a curtain, shear is the lateral force that snaps a brittle screw  .

There are structural screws, these will have an ESR number or approval on each box, fastenmaster, grk, simpson sds. These are the new timber screws, they replace lag screws which are ductile fasteners listed in the NDS with tables of strength, etc. The timber screws do not require pilot and lead holes and are often cheaper, definitely so if labor is paid for. I keep a box or two on the job, ran a few today. I do use deck screws in withdrawal only situations or to tighten up framing but they are not load carrying. I've replaced deck screws on decks that snapped under the shear force of drying wood, and not just a few. The old soft wood screws that stripped out under the driver and led to the hardened screws... they are fine, they're ductile. They'll earn you a failed inspection most likely and you'll cuss the entire time. Deck and drywall screws are the brittle ones but you really don't know much about the steel in an unlisted screw.

Substituting a larger brittle screw doesn't get you there, we want a building groaning ductile failure that screams "Get Out!" not a brittle failure that simply goes Whump!

Home demonstration, drive a nail and a screw side by side into a board and strike each back and forth sideways hard, count the number of licks each can take.

Please post the cite to the Florida sheathing requirement, read the footnotes, I'm betting that was a misread. Sheathing is a shear brace and a non rated screw would be the wrong thing to use. Deformed nails, ring or screw shank would be fine, it's the steel.

In large timber construction like bridges you see the lag or bolt (A35 steel), what you don't see is the spiked shear plate or split ring shear connector that the lag or bolt is tightly sandwiching inside the joint. A nail or spike cannot reliably hold the joint together through moisture cycling enough to keep those shear developers in place to do the real work. This is akin to folks seeing a piling buried 30' deep, burying theirs 3' deep and thinking they have done the same thing.

Is anyone interested in further reading on connections?

[JRR]

If screws are inherently weaker ... why the sudden popularity of timber-screws? 

Uhh...there are a lot of thing that have sudden popularity that are not popular because better. So I guess the operative word here is popular with whom.


Assuming this is a question:  I don't know who they are popular with ... unless I could answer with, "customers".  I don't remember seeing them in local big box building supply stores, say, five years ago.  If I wanted some, they were a special order item.  But today the local (Atlanta) HD, Ace, and Lowes have them in several lengths on the shelves along with other fasteners.  Since they have recently appeared in numbers, I assumed they were now "popular" ... perhaps a careless conclusion.  And with what population sub-set?  I don't know.  Perhaps: Folks who want them.

[Don_P]

I love 'em. I first got them with log home kits as an alternative to lags. It turned a tedious operation that took about a minute per lag to one that took seconds per screw. We still kept a few hundred lags on hand to pull down pesky logs but they do a good job. They next found a place as an alternative to lags or bolts for fastening deck ledgers. It takes 2-3 times as many but is still faster. If I'm lagging a porch roof ledger to studs I never was keen on a big honking lag, the much smaller ledgerlocks are a great choice there. Screwing Sips to a timberframe with the big flathead sdws's or purlins to a built up roof, we used to beat in 12" 80d ring shanks by hand, talk about sore arms. Every fastener has its' place  .

[Erin]

Sheer is a curtain, shear is the lateral force that snaps a brittle screw

Doh!  I hate it when I miss those!


Timberlok (I think that's the brand name I'm thinking of) screws are increasingly popular.  They're specifically marketing toward deck construction, for those who haven't seen them.  Supposed to replace lag bolts.  They advertise in magazines like Journal of Light Construction and Fine Homebuilding and if I'm thinking of the right thing, they've even shown the numbers that show why they're as good as lag bolts. 
However, that's a very specific product, not just a standard screw, and I'm going to take a guess that they ain't cheap...

[Don_P]

It's one of those words I've seen interchanged a whole lot lately, I guess the school marm came out in me  .

1/2" lags and bolts can get pretty spendy too. This months Fine Homebuilding has a cost breakdown but I think they are a bit high on the lags. I've got pt on Thursday and need to go to Lowes to pick up what I forgot today  , I'll try to remember to check prices. Course if I could remember anything I wouldn't be needing to go back. Back in the day I was buying lags by the thousand and that got it down but that is a lifetime supply for most folks. Hmm, CP co-op?

[Pine Cone]

Timberlok (I think that's the brand name I'm thinking of) screws are increasingly popular.  They're specifically marketing toward deck construction, for those who haven't seen them.  Supposed to replace lag bolts.  They advertise in magazines like Journal of Light Construction and Fine Homebuilding and if I'm thinking of the right thing, they've even shown the numbers that show why they're as good as lag bolts.
However, that's a very specific product, not just a standard screw, and I'm going to take a guess that they ain't cheap...

1/2" lags and bolts can get pretty spendy too. This months Fine Homebuilding has a cost breakdown but I think they are a bit high on the lags. I've got pt on Thursday and need to go to Lowes to pick up what I forgot today  , I'll try to remember to check prices. Course if I could remember anything I wouldn't be needing to go back. Back in the day I was buying lags by the thousand and that got it down but that is a lifetime supply for most folks. Hmm, CP co-op?

The Log Home Store has Oly Log Screws that appear to be the same as the Timberloks.  They also carry Log Hog screws which have a larger diameter.  Price isn't too bad if you buy the boxes of 250.  I used a lot of these in 4" - 16" lengths on my cabin.  I used the long ones to help hold my log walls together, but used the shorter ones as a lag-bolt replacement.  Used a Chinese Hole Hawg copy to screw them in, a very powerful drill, and I think I only broke one log screw out of the 700+ log screws I used.  They are very strong.

http://www.loghomestore.com/1746-oly-log-screws.php

In many cases, screws will never replace nails.  I started my build using lots of screws and by the end of my build a few years later I was using far more nails than screws. 

[MushCreek]

Not all screws or nails are created equal. There are malleable screws, and there are brittle nails. The key is to look at what they are approved for. Simpson makes connector screws, for example, which can be used in the place of nails, but they ain't cheap.

[Squirl]

Is anyone interested in further reading on connections?

You know I do.

[alex trent]

More info is always good.

When I was building I did a fair amount of research on nails as i had to bring them in from the States and figured I may as well bring in the best. Also was using green lumber and had some unknown qualities so i though best nails would be best.

I ended up with ring shank or spiral for all but a few uses. HDG. Mostly hardened. The cost differential is small or such an important component.

In looking I found an amazing about of difference in shear values in 16d nails...like 5x.  True, the manufacturer values are only part of the shear equation, but it does count. Was hard info to get from some. my main supplier was MAZE nails..great stuff. GripRite never answered any emails.

[flyingvan]

  Another good test (instead of whacking it with a hammer) is build a square out of 2x4's with each side being a few feet.  Do two diagonally opposite corners with screws and the other two in nails.  Set it on a corner and push down, see which corners fail first.
  It's true, though, there ar places you want the stiffness---like in some places for shear transfer.  Deckboards, too, since flex at that point isn't important and nails (if driven in straight) will work their way out. 
   If the only reason you're choosing a screw is the issue of a nail backing out, driving a nail in at an angle helps keep that from happening
   In fixing old broken stuff I can't recall coming across nails that had failed, but I can think of quite a few screws that had.  I also think nails are kinder to wood fibers than sharp screw threads are.  Buildings are always moving, expanding, contracting, and vibrating.

[zion-diy]

Our house is built entirely with screws. The only nails were a few finishing nails, and the roof nails holding the shingles. It's been up since 2005 now and has survived an f4 tornado passing 800 yards away with only a few shingles taken off. (knew I should have screwed the shingles down)  It has survived all kinds of winds, snow, and everything else nature has thrown at it.
Put me down as one who believes in screws.

[JRR]

.... f4 tornado passing 800 yards away with only a few shingles taken off. (knew I should have screwed the shingles down) ....

What were you THINKING!

I also have an all glued-and-screwed cabin that has impressed us in high winds.  Rock solid so far.  .... and my shingles (corrugated metal) are/is screwed down.

BTW, that is very nice looking digs!

[alex trent]

For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the message was lost.
For want of a message the battle was lost.
For want of a battle the kingdom was lost.
And all for the want of a horseshoe nail.

Don't lose you kingdom...use good nails.

If you are worried about nails pulling out, use ring shanks.

[JRR]

I don't worry about nails pulling out ... ain't got any nails!

Years ago, I used to wear shoes that had nails.  Most everybody did.  Nails held the soles to the rest of the shoe.  Once I had one of those nails protrude upward, I hardly noticed until I could hardly walk.  It was in my only footwear, my motorcycle boots ... and i was on a several state tour ...with no time to stop and buy new footware.  By the time I got back home, I had a severe heel problem.  What does this story have to do with anything?  Not much.

Except it is a happy curiousity that most footwear, today, is generally more serviceable, more comfortable .... and usually is manufactured without nails.

.... so there is hope for homebuilding!

[Don_P]

There is a good online course on connections at apawood.org
Click on the "wood university" tab bottom right of the home page, sign in and take a look at course 201. For some of you this will have a lot of review information, but worthwhile, I'm going through it again now.

The connections calc at awc.org is good, it is under the "codes and standards" tab > software.
It contains the same info that is in the NDS connections tables.
Go ahead and set up a wood screw example (yes, wood screws are allowed) hit the calc button... now read the first footnote, there is the problem with deck and drywall screws. Email the manufacturer and ask for the bending yield strength information and file it.

The problem is with the mode of failure, drywall and deck screws fail suddenly. A ductile failure is what is desired. This graphic from the course above does a good job of explaining;