Screws vs nails in wood. 4

[fastline12]

This has been a long standing discussion I guess. I am working on a pole barn for myself and strongly considering screwing all of my purlins and gerts instead of nailing. I know some feel ring shank and glued nails hold as well but I commonly have told people to get their nail bar and remove a screw. I also am considering the considerable seasonal dimensional changes of lumber. Just because a nail is tight today, does not mean it will be tight in 20 yrs. The same may be true for screws though but at least the threads will have much more bind than a smooth shank.

I am curious of any other opinions on this matter. I would be securing 2x4s and 2x6s.

 

[MintJulep]

Sure, screws are probably better.

But if nails are good enough then the betterness isn't really worth anything.

 

[MadMango]

Walk along any seaside boardwalk and you'll find plenty of screws.

"Art without engineering is dreaming; Engineering without art is calculating."


Have you read faq731-376 to make the best use of these Forums?

 

[KENAT]

forum507 might be a good place to ask folks that deal with this on a regular basis.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[IRstuff]

Over time both will loosen, but I think screws take longer time to loosen. Hammerclaw removal of screws will result in more damage to the underlying wood that wouldn't necessarily get replaced in a refurbishment.

TTFN
faq731-376

 

[dgallup]

We have been building floating docks completely with screws for about 20 years and they hold up a lot better than nailed construction ever did. The outside frame corners are bolted through angle iron but the rest is held by screws.

They get hauled out in the fall and go through a Canadian winter on land then go back in Lake Huron and get worked by the waves for about 6 months each year.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[MiketheEngineer]

Screws!! Because if you "screw up" - pun intended - they are easier to remove!!! Or if you ever want to move or rebuild the building.....

 

[SNORGY]

I know it's not the same but after my first two years on the acreage and several miles of board fencing in my lifetime, and one very sturdy horse shelter, I would never choose nails over screws in anything I ever built.

Regards,

SNORGY.

 

[moltenmetal]

Screws have more withdrawl resistance than nails, but we usually don't design wood construction details to depend on withdrawl resistance for safety. Most joints that hold anything up are pinned, with the fasteners in shear.

Screws excel where withdrawl resistance is key, i.e. holding down flooring or deck boards etc. They're also great when easy disassembly is your biggest concern- that's not typically a big issue in permanent construction though.

Screws, when compared at the same outside diameter as nails, have GREATLY less section thickness to resist shear. So when people replace #11 hanger nails with #8 screws, for instance, they're not getting a detail with the same strength.

Screws are far easier to install with long-term corrosion resistance. Nails in ACQ-treated lumber, for instance- forget about it. Coated or stainless screws are king in that service.

Screws are usually made out of greatly more brittle material than nails. A typical #8 x 3" deck screw can be snapped off with a single hammer blow. That matters in some details, and doesn't in others.

Screws cost more and take far more time to install than nails. A proficient carpenter with a hammer, much less a pneumatic nailer, can easily out-pace a guy with an impact screwgun.

If you use enough screws of the correct size to be equivalent to the nails you're replacing, screws are a perfectly acceptable alternative to nails.

 

[MiketheEngineer]

Molten brings up some very good points. IF I am building tract houses - give me a pneumatic nailer and I will go to town. If I am building a couple of walls in my house - I screw it every time.

 

[jgailla]

I was laid off a couple of years ago and in between jobs worked construction, mostly wood stud framing.

The guy I worked for was a complete nutcase. He wanted all the walls plumb to within 1/16", joists/trusses (not furring) shimmed to within 1/16".

After ripping out a wall or truss for the tenth time, I started doing everything with screws. Easy in, easy out. I never used another nail on the job.

I worked on the job for a year and we were still on the same wing of the house. He was working on cost-plus so I guess he had these rich owners snowed for the time being.

 

[SnTMan]

jgailla, just curious, how were you "able" to measure framing to that degree of accuracy?

Regards,

Mike

 

[KENAT]

He bought a tape measure with more lines on it obviously;-).

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[jgailla]

Of course we were not "able" to measure the framing to that degree of accuracy.

We would use a laser level, set off a certain amount from the floor plate, say 3 inches, mark the ground, set the laser on the mark, and then measure with a tape off from the top plate to the laser beam and make the top plate 3 inches from the laser.

For horizontal elements, we used a transit laser and handheld receiver in conjunction with a tape butted to the horizontal element in much the same method.

Now, if you measure this way and move things around a little, you can make it "good" to within a 1/16" for anyone who has no conception of repeatability or precision.

The problem comes the next time anyone tries to check it. The process itself is no good to at least 1/8", so the company owner would check it and send someone else to "fix" it. You can see how this process could be repeated ad nauseam.

The guy who owned the company was an accountant with a rich father who for some reason unknown to me decided to get into construction. When I worked for him he was on his third project. At least one of the other projects was building a house for his father, which may explain how he was able to stay in business for a few years.

In addition to all this, the guy was emotionally unstable and would occasionally lose his temper for no reason and send everyone home without pay. Meanwhile I can't quit because jobs are scarce and I still can't make enough money to pay the bills on a sharply reduced income.

Sorry for the rant. This was a bad time in my life and I'm still bitter.

 

[jmw]

Before I got a proper job I was a "nail driver" with a house builder in Georgia.

Balancing up in the rafters and measuring up for the fillers I called down a measurement accurate to the nearsets 1/16thof an inch to the sawman on the ground and the boss intervened.

"You're a god-damned nail driver, not a cabinet maker." He then corrected the measurement to the nearest 1/8th - you go to the nearest 1/8th and call it "full" or "shy".

This was in the days of manual hammers..... you know, that metal lump on a stick you bash the nail or screw with (yes, I know some people who install screws with a hammer).
You learn how to drive a nail with only one or two hits and leave an owl eye to lessen the chance of t sweating out.

(The only question I wanted to ask was why, in a country with so many termites, are so many building built of wood?)

Oh yeah.
Nails are quick and cheap and effective for framing.
But when it comes to roof work, or anything off the ground you tend to doubt the value of nails.
Scaffolding boards ("walk logs" in redneck) don't rest on scaffolding but on metal frames nailed to the side of the house.
Since this means the nails are subjected to pull forces rather than shear, every so often the top nails would pull out and dump the worker on the ground far below and shower him with "walk logs".
It was no accident (well, it was if you know what I mean) that the boss and his son were both on crutches when I started there.
It isn't helped when the frames are nailed to the studs through 1.5" polystyrene insulation.
Nails hold best when the two bits of wood joined are held tight together by the nails and under some compression.

JMW

http://www.ViscoAnalyser.com

 

[MiketheEngineer]

If you are stabilizing scaffolding with nails - be prepared to die!!

 

[rconner]

Great thread to read (and learn,have a good weekend!)

 

[fastline12]

Obviously nails in shear perform well. However, my post was targeting the purlin and gert installations on a pole barn in which the shear is not as important as the pull stress in a wind storm. I am still trying to find video of one failing but I think it is fair to say an up draft or lifting force on the roof is usually what does them in in which the roof is removed. The purlins will peel off super easy.

I am considering "flush mounting" the purlins so instead of laying them on top of the trusses like is typical and easy, I would cut and saddle each 2x between the truss top chords where nails would then be in shear.

however, I am not immediately convinced that is worth doing. As one mentioned above, if it is not needed, it is not worth it. I was looking to attach with screwed in which if you use a decking screw rig attached to a drill, the extra time will be measured in minutes.

The trusses certainly are not coming off the main poles without a catastrophic failure so if I can keep the purlins and gerts on, that means the sheeting should rip off and I replace it as needed in a major storm.

Lets keep it relative though. 150mph is target. More than that and I am just grabbing my angles because mother nature trumps engineering every single time.

 

[jmw]

The frame is like a shelf bracket you put on the wall.
To be fair they'd usually hammer in a bunch of nails through each hole and turn the ends over (I think the designers probably intended them to be fixed with coach screws).
At least when I worked with my Uncle he used proper scaffolding.
Oh, and If I said 12" and 7/16ths he wouldn't question it. He and his partner were highly sought after craftsmen. I learned a heck of a lot more working with them for a couple of weeks than with the building contractor all through that summer. (I also learned that a Georgia Summer is no time to have an out door job).
(Oh yes, I was not only a nail driver I was also a mud man when necessary. Mud is Redneck for cement).

One good thing about my Uncle was he only trusted what he knew from experience was safe and reliable, which included his blue Chevvy '57 pick-up. It's probably still running.

JMW

http://www.ViscoAnalyser.com

 

[fastline12]

Before we put this to bed looking at shear and pull, probably the most important factor is fatigue life. Structures move so the fasteners will to. I realize nails do much better in this area but not sure on screws. I know they are harder which is not all that great. I still wonder why they do not do an induction harden just on the head so they will drive, yet leave the rest alone for better fatigue life. I guess probably the strength needed to drive the screw in he first place.

The defense of nails is usually fatigue life but I have to wonder if modern screws have improved there?