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I am planning a deck with dimensions of 14' x 20', where that is 14' out from the house, and 20' along the house wall. This will be an elevated deck with 2' of that outward span cantilevered. The plan calls for 16" OC joists and blocking at the halfway point of the span.
My question is about creating the stiffest feeling for the deck. Basically, is it better to do more blocking or 12" OC joists? I don't want that "springy" feeling at all. Nice and solid.
Deeper Joists
I assume that you've spec'd at least 2x10s for a 14' span. Bump to 2x12s on the same 16" centers for a noticeable improvement in stiffness.
More Joists
Taller joists offer a greater stiffness gain, but if height is a concern you could use more joists (say at 12" centers). The main drawbacks are cost and appearance, as you'll use more materials and have more screw stripes across your deck.
Thicker Decking
By tying the joists together more robustly you split load between joists better. 2x6 lumber is much stiffer than 5/4. The main drawbacks (aside from cost) are that you'll need longer screws and the appearance won't be as polished (edges are typically sharper and not as uniform).
More Joist Blocking
More blocking will have a similar effect to using thicker decking, spreading load among more joists, with none of the appearance compromise. Install two or three runs. It's more work, and you do need to fit them well. You'll use many more screws and quite a bit more lumber
Give a short and simple answer because you have a relatively common deck size. 16" OC is fine. Put two rows of blocking with the same materials as the joist. The blocking should split your deck in thirds. If done well the blocking will appear to be some sort of magic beam that goes through your joists.
I mention that because I always add at least one row of blocking to all decks. You do not want your joists turning on you due to moisture/humidity issues. The best way to combat this is blocking. Therefore you need to do it anyway and with 16" OC you should have little to no deflection give you are using at least 2x8 on top.
Note: I want to add that your piers probably play a bigger part in the apparent "stiffness" of a deck. Any kind of sway in them and your deck will have a bouncy or flimsy feeling. This may mean that you want to sink your piers a little lower, get bigger piers/lumber and ensure that they are set correctly. If these things have any given your deck will always have give.
If you want NO springy-ness ( is that a word?) I would consider using 2x12s (and ensuring supportive posts/columns are also beefed up to support the additional weight load). 12" o.c. would work as well--but the same caution about posts/foundation should also be taken.
If you ever plan to put a hot-tub or other heavy load on it, I would use 2x12s on 12" centers--or consider use of steel I-beams --@ 6ft and 12ft from home (with I-beam columns). Depending on your location, steel MAY be the cheaper option. (delivery costs are not insignificant).
I also would use 2x6 for decking (and use stainless steel screws for the all construction--costly? yes. But you won't regret it).
What are you using for support posts and foundations?
