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I'm working on designing the support frame for a deck for my backyard.

The basic shape of the deck:

enter image description here

It's essentially a square with one corner chopped off. The red line is the joist in question, the green lines are the remaining joists and the yellow(ish) lines are the stringers in between.

My question is how do I attach the red line joist to that corner joint? I'm pretty sure there are 45 degree angle joist hangers for the rest of the joists. Is this the best way to lay them out, or is there a better way to arrange the joists? The decking will be installed perpendicular to the joists, or parallel with that one chopped off angle. The joists are on 16" centers, measured off from either side of the red line joist. The drawing is oh so very not to scale :)

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I guess I'm curious why you wouldn't simplify the layout like this:

Yellow = deck joists

Green = support beams

Deck Drawing

Your decking would run diagonally over the joists. If you use 2x boards for decking, that should be fine if the joists are 16" on center. If you want to use 5/4 decking, you should probably put the joists 12" on center so that the diagonal run is closer to 16".

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  • @Eric - I was under the impression that the decking had to be perpendicular to the joists. Also, since this deck is pretty small and very low to the ground (pretty much ground level at the bottom of the joists) I was planning on just using pier blocks at each of the 5 corners, no support beams. It's about a 12.5'x 12.5' deck.
    – morganpdx
    Feb 23, 2011 at 21:04
  • @morganpdx - no, the decking doesn't have to run perpendicular to the joists, you just don't want it to span more than 16" or so unsupported. If it's that low to the ground, you could do away with the support beams and use piers in the corners, but I might recommend putting a pier in the middle of each of the yellow joists as well, depending on what size joists you'll use. A 2x10 should span 12.5' no problem, but anything less and you'll want a support in the middle.
    – Eric Petroelje
    Feb 23, 2011 at 21:17
  • @Eric In that case, thats exactly what I'll do. I'd like to keep it as low as possible, so I was planning on 2x6's; I'll pick up a few more pier blocks. Thanks!
    – morganpdx
    Feb 23, 2011 at 21:23
  • 2X6's at 12 feet will bounce like a trampoline
    – shirlock homes
    Feb 23, 2011 at 21:34
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    @morganpdx - if you are using 2x4 cedar decking, you can go 16" on center. The important thing is how far the boards span unsupported. When you run a board perpendicular to the joists, the span is simply the distance between the joists. When you run it diagonally though, the span is a bit further. With joists 16" on center and the boards running diagonally, the unsupported span is about 23".
    – Eric Petroelje
    Feb 24, 2011 at 14:04
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Your original design is fine if you are comfortable cutting the angles on the joists. (your pic is a bit confusing) You can install a ledger board on the wrap joists (frame) for the floor joists to rest on. You can then use hurricane straps to further secure the joists to the frame. Some cross bracing would also be advised. There is nothing wrong with Eric's suggestion, but keep in mind that even with joists 12 inch OC, the nailing is apx 17 inches on center, not really a problem with 5/4 decking. Also, 12X12 isn't really that small. I'd be using nothing less than 2X10 joists and 2X12 wraps with ledgers to assure a flex free deck. If you want to use smaller joists etc, use a center double 2X6 perpendicular beam, posts and ground supports on the ends and center. This is very little more work, but will make your deck really strong when you have a dozen friends over for your first BBQ... BTW I have built dozens and dozens of decks, trust me on this one. Good luck.

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