I'm planning to make a 16'x16' ground level deck overtop an existing 12x12 concrete patio extending into the yard 4 feet on two sides. Id like to keep it at around 9 inches off the ground so I don't need to make a step, and to keep it under my 13 inch door clearance.

Crude Drawing

I've been trying to find a way to hide the deck blocks / supports under the deck (effectively cantilevering it on all sides). I had found this post https://diy.stackexchange.com/a/192122 which shows how to do this on a smaller deck by, making flush beams parallel to the joists and using upside down joist hangers to attach a doubled up rim joist to those beams.

I wondered if the same would apply in my situation just at a larger scale.

Deck design

I'm planning to use all 2x8 GC PT construction. The red beams would be resting on 2 supports each for a total of 12 supports. The blue rim joists/beams would be connected to the red beams with upside down joist hangers to distribute the load into the red beams. The outermost joists would be connected to the blue in the same way.

For supports on the concrete portion I'm planning to use these adjustable pedestals. I've called the company and verified they can be used as supports for 3 inch beams like I'm proposing. For the part in the grass I would just use precast concrete deck blocks with packed crushed stone under them for leveling and stability.

Will my design work and be structurally stable?

  • should work, have you run your spans against the tables in the american wood council prescriptive deck design? cms7files.revize.com/watertownct/Departments/… Mar 23 at 18:11
  • @FreshCodemonger Yes I have, for southern pine 2*8 joists at 12"OC it was 13' (I'm under 8'). And for a 2-2x8 beam spans between supports it was 7'4" with 8ft joist span, so I'm planning to have 12 supports total 2 for each red beam which satisfys the 7 foot max span and the red beam spacing satisfies that same max span for the blue beams.
    – Zooloo10
    Mar 23 at 20:12


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