Is there a case where nails are better than screws, from a structural standpoint? For instance: Say you used screws instead of nails on a backyard deck, when the design specifically called for nails. Would the result be inferior? Could it fail inspection? Would nails absolutely be preferable in this instance? Are there any rules of thumb about when to use screws vs. nails? - Chris W. Rea
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kkeilman Answers:
Screws are a "superior" fastener over a nail (they have far superior tensile strength)?especially if you're talking about screwing down decking. However there are many scenarios where a nail is the proper fastener for the application (attaching joists is one example?screws are brittle and will fail when subjected to the forces of a shear loaded application).
Using your deck example?you should use nails to attach the joists to the deck framing but use screws to fasten down the decking itself.
decker Answers:
Nails are used in almost all framing and structural applications. Most code books are designed with nails in mind and will have specific minimum nailing requirements and patterns for different applications.
Structural screws are coming more and more on the market every day, but because most code books don't include them you will need an engineer's approval of their use to pass inspection in many cases. If you want to use structural screws without paying the big $$ for an engineer you should talk with your municipal build dept. first to see if they will allow it.
Your normal wood screws are not structural. Standard screws are brittle. If you take a normal screw and drive it part way in and whack it with a hammer, it will snap. If you do this with a nail, the nail will bend. Which would you rather have holding your deck up? Something that bends but stays intact or something that can snap?
I mostly use screws only for temporarily holding things in place while I nail stuff up and for the decking surface. However, on one deck I built last year I used a ton of structural screws. I have a couple of times had the head snap off of a structural screw when driving them in, and three of them snap when a small machine hit some lumber. While undoubtedly considerably stronger than normal screws, this leads me to still question their shear resistance.
In the end: nails, hex bolts, and lag bolts are still better in most applications. Structural screws are just easier than bolting and cooler than nailing. I do love using them, but they don't (and shouldn't) completely replace traditional fasteners.
user2091 Answers:
Screws can be easily removed. I really believe this is reason #1 to use screws. I think of everything as a work in progress. I never know whether I will need or want to change work I've done. The future is uncertain, thus you should always choose to screw when possible. Also, when screwing or nailing, I often screw up. With screws, you simply remove them and fix the problem. Removing nails may lead to damaging your project. Screws are much easier to control. Whether using a hammer or nail gun, exact placement of a nail is almost impossible. Screws don't really suffer this limitation.
Danny LeBlanc Answers:
One thing that no one has mentioned: screws WILL NOT pull down a deck board nearly as tightly as a nail. If you have a twisted board or a board with a crown, a screw is pretty much useless.
Screwing deck boards also creates large holes for water to soak into and rot much faster. Using a 3-inch galvanized nail and nailing it flush will pull the boards tighter versus sinking through the wood. The decking will last longer (same concept as wood siding) and last but not least, come on guys, a nail looks better.
Jeff Widmer Answers:
Screws would tend to be slightly thicker than nails (because of the threads) so you would probably want to watch out for splitting of the wood and might want to require drilling pilot holes if you switch to screws. For the most part though, screws would work better than nails in the long term (would not pop up over time) but would be harder to use (pilot holes, snapping, etc.) during the installation for your backyard deck.
BUT if you have some sort of project that is supplying the nails/hardware then I would be cautious about swapping out one sort of hardware for another. The pre-supplied product could have been specially chosen for the job and so you would not want to go and swap it out because you think it is better to have screws. One such example would be some wooden playsets where all of the hardware is supplied. Make sure you use what they give you (and what the engineers said will work).
Illustration by Sean Gallagher.
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