A fairly common topic this one and one that often sparks huge debate amongst professional deck fixers, tradesmen and renovators. I guess the right answer is ….there isn’t one, it’s largely down to personal preference and there are pros and cons for each. Firstly it should be borne in mind that there are lots of factors that affect choice of fixing such as, the location, type of decking timber, type of joist timber, finish requirements, exposure, labour and of course cost.
Generally speaking nails are much cheaper to buy and a lot faster to lay, typical deck nails should be rounded or rose headed with a twisted shank to grab the timber and they are usually fitted in hardwood decks by predrilling the timber and then hand nailing, nail guns can be used if the nails are specific for decks but beware of using standard nail gun timber nails, they are fast to fit but simply not suitable for the purpose and will lead to problems later.
Screws give a far better fix, however they can be more expensive and a lot slower to lay, they have considerably more longevity once installed and are unlikely to need any maintenance. The most common guage of deck screw is 10g (or 5mm) with a 8-9mm diameter head so they gain a lot of strength in the body from the thickness and create a lot of hold down force in the board due to the size of the head.
Nails can be far more unobtrusive than screws although screw heads are available in smaller sizes for a more aesthetically pleasing look. Dependant on your climate, nails can require a considerable amount of maintenance and if you live in a hot temperate area then I wouldn’t recommend nail use at all. The following images are from my own personal decks, there are 2, one on an upper level which is fully exposed to the extreme Australian summer sun and humidity and a lower ground floor deck which is mostly shaded, they have both been nailed and are both 19mm hardwood on softwood structural joists.
The nails ‘walk’ out of the timber creating loose boards and splits and lifting above the surface, they need punching back down approx every 4 weeks in summer to prevent injuries to bare feet.
The ends of the boards start to lift as the nails lose there grip in the support joists.
The nailing and then re-nailing operation can lead to splitting of the joists and subsequent loosening of the nails.
The boards can start to ‘cup’ and lift at the more exposed ends leading to trip hazards.
A run of nails ‘walking out’ of the boards, these are pretty dangerous, I can tell you from experience they hurt when you catch your feet on them.
A less exposed ground floor deck also shows signs of lifting nails although not as extreme as the deck with direct sun exposure.
My conclusion, from personal experience, is that nailed decks are simply too high maintenance, nailing doesn’t provide enough hold for the constant timber movement in high temperature zones and the deck needs constant checking, particularly if there are children around. Screws offer a far more professional and permanent fix, they may be more expensive, slower to lay and maybe aren’t as attractive as nails which can be ‘lost’ in the finish, but once there in that’s it done. It’s simply a no-brainer in my opinion.