I have a deck that is old and falling apart so it is time to replace it. To replace the deck boards I plan to remove existing, measure boards, cut new board and put the same size and board back into place. The deck hasn't been replaced in twenty years and it currently has nails. Many tutorials and research show using screws. After a search under the deck tag I didnt see any questions on why screws would be better then nails other than I would imagine over times nails could back out. So why are screws better for deck boards then nails? Is there a particular screw other than a normal wood screw that would be good for decks?
Not the best answer, but:
Use screws on the top boards where people will be walking barefoot. Every kid has had a wicked gash from nails (naturally) poking up a bit.
Use big a** nails to attach your cross beams to your main structure. Nails are only good at holding against a shear, i.e. nails should always be (and only be) parallel with the ground.
Use large lag screws to hold together your 4x4(?) frame, the main, big parts.
Your deck will experience changes in temperature and the wood and fasteners will not adjust at the same rate. You want some give in a deck because of this. You also want some give because of the sporadic forces that humans will put on it. Nails provide some give. Screws provide absolutely no give; they will destroy the wood around before they back out.
Putting screws on the "floor boards" will wear out the boards faster, but in my opinion that is the sacrifice to prevent injuring the fragile humans.
Please also see this question. Those people are much smarter and concise than me.
Agreed, use screws. Nails will pull out, and the shrink/swell cycle as the wood dries then gets wet then dries again can work the nails out of the holes, and make the holes slightly looser. Screws can't be pushed back out. They'd have to be twisted out, and the lengthwise force on the flat helical edge of the thread from tightening the screw down will remain for a very long time.
However; this probably goes without saying, but use the right screws, and the right hangers and other hardware.
Since chromated copper arsenate (CCA) has gone out of favor for pressure-treating lumber, the replacement chemical cocktails are more chemically reactive with zinc and can cause faster corrosion (destruction in years instead of decades). Your screws aren't going to hold if they've rotted into flaky rust all the way through, and if your joist hangers rot away your deck will collapse.
Some (most?) manufacturers of hot-dip (zinc) galvanized steel parts generally won't warranty how long their products will last in contact with pressure treated lumber. The zinc is sacrificial, so it gets corroded instead of the underlying steel. But the copper in the pressure-treating chemical brew will corrode the zinc forever, then the steel underneath will rust away. Still, even if the product has a lifetime warranty and you can get service despite using the parts with pressure treated wood, it probably means the manufacturer will replace the parts. They won't rebuild your collapsed deck. You'll have to do that yourself.
Galvanized parts are probably fine if you're using natural cedar or redwood because there aren't added chemicals that will attack the zinc coating.
The newer thing in coated parts is polymer (plastic) coated hangers and screws, or zinc-and-polymer coated parts.
Stainless steel is probably best for corrosion resistance, but expensive.
The issue with decks is that they are outdoors, which means they will tend to expand and contract a lot with moisture and temperature changes. This will cause nails to come loose.
The best thing to use is a bolt and washer design, because it can be made to flex naturally.
Since it would be time-consuming and costly to bolt down every single board on the surface of the deck, the cost-effective alternative is a screw system system of some kind on the deck, using counter-sunk bolts only for the structure.
You should use a stainless steel, silicon bronze or brass screw system like Tiger Claw. Modern lumber is ACQ treated which will rapidly degrade any galvanized fastener.