I’m adding on to an existing deck for an old customer who’s moved into a new house. The new beams will be 2x10s, the joists 2x8s, and the decking itself will be 2×4 cedar to match existing, but I’ll run it at 90 degrees to the existing deck — it’s going to stand out as different for a year or so, so I’m not going to try to hide it.
Here’s the challenge: I’m building flush to existing. One rise up or one rise down is not an option, and I wouldn’t build that anyway, one rise is way too dangerous. The new, wet ACQ will shrink a lot — I’m guessing 5/8†or so. The fact that local inspectors no longer allow bolting to the sides of the posts means that every bit of that shrinkage will lower my new deck. It also removes the possibility of re-bolting after re-leveling next year.
I’m thinking of setting the framing high by at least a fat 3/8â€, and cantilevering my joists past the beams enough that I can tie their ends into the existing framing. That 3/8†will then be feathered out over the 5’ cantilever, sloping gently up for now, and maybe sloping down 1/8†to 1/4†in a year or so.
Where I attach to existing, I’m not going to use hangers: I’ll probably have to tweak the level next year after my 2x8s shrink, and I can’t find any screws approved for hangers. Actually, that’s not true. I found a website in New Zealand that offered some, but this is Michigan.
So I’m thinking double up the existing single 2×8 end joist with a 2×12 for my bond. There’ll be plenty of room o that 2×12 for a 2×4 ledger under the ends of my new joists. I’ll attach the ledger with GRK lags. Next year I can get underneath with a screwgun and a jack, and work my way along flushing everything up again.
Any suggestions out there? Ever tried something like this before? And does 5/8†shrinkage sound right for 2×10 + 2×8 + a 2×4 on the flat? Maybe more like 3/4â€?
AitchKay
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Can you find lumber graded KDAT, kiln dried after treatment? Not the expert but your shrinkage seems a bit high to me.
If I understand correctly why can't you attach the cantilevered ends of the joists to a ledger/rim joist and bolt it to your existing rim. Then if necessary unbolt, jack and rebolt?
Where your beams sit in the notched posts why can't you jack, unbolt, shim the notch, and rebolt in a different hole?
Thanks, rasconc,Yeah, I've considered those options.I don't know of a local KDAT source, but it's worth a few calls. More expensive, though, and I'll bet I still have to tweak next year. I thought that jacking a whole new rim would be too heavy/unwieldy, but I know I could remove bolts one section at a time, and there certainly would be less fasteners to deal with, and fewer jacking points necessary. Maybe I'll do that.As for the posts, they'll be square-cut factory ends, with the beam sitting on top (I always put mysite-cut post ends in the ground where they won't rot). If I could find rated screws, that would make it easier to remove my Simpson connectors. But if it settles too far, I'll just trash the connectors, and slip in a stainless shim plate, and put on new connectors.So, while I'm going to build high, I'd rather end up a little low than high next year, because shimming up will be easier than cutting down.And the more I think of it, you're right, unbolting and jacking the rim is the way to go.AitchKay