I'm in the midst of tearing apart my old deck down to the frame to replace the decking, railing, and stairs. The old decking was 2x4's. Now having taken most of them off, I've found that the structure underneath was built at two different times. So I've got half a deck with 16"oc and the other half with 19.5"oc.
My question is what thickness of decking do I need to for stability with the 19.5"oc., is 5/4" thick enough to prevent sagging and bounce? I was thinking of 5/4x6 in 10 ft lengths. (Deck is 27.5'x8.5').
I've seen 5/4 on 24" centers, but I'd never build it.
On 19.5" there will probably be some flex.
I think it's a matter of your tolerance.
Why not grab one 10' 5/4 from the lumber store, throw it on the deck and walk on it. Get 2 people to stand on opposite ends to mimic the fasteners that will be there, if you have the extra bodies.
Personally, I think it'll be fine.
Don't see 19.5 very often though.
Are the 19.5" OC joist fastened using joist hangers? If so it be pretty easy to reposition/replace the joist so that they too are at 16" OC. You might end up with an oddball spacing at one end, but it would take care of those deflections concerns so part of the deck will not seem bouncy.