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I have a sunken backyard concrete patio which is sloped for drainage. The slope reduces usability for sheds, BBQs, picnic tables, etc. The space is approx 15' x 25', with concrete walls on 3 sides. The 4th being the house (wood siding).

The back door opens out onto a concrete step/platform which then drops 7-1/4" down to the patio. The first step of the stairs on the other side is 7-1/4" up from the patio. The max depth from this level line is 10-1/4".

My plan is to use 2x6" joists 16" OC running from the house to the retaining wall (15'), attached to joist hangers on a ledger (bolted to concrete wall). The joists will support 2x6 or 5/4 deck boards (undecided). All joists/ledgers will be pressure treated.

Q: Can I run a single joist 15' from one side of the patio to the other, or do I need a beam half-way across, or maybe blocking between each joist?

I am also considering adding footing to the joists to help with support. Either leveling feet, MRP pedestal supports, or scrap PT 2x4 cut to size as a "shim".

leveling feetjoist pedestal

  • 2x6 joists will not span 15'. You'll have a trampoline. Be aware that you can't fasten a deck to a house or its foundation unless it has full and proper frost footings. (Maybe that's not what you meant.) I would not add support to individual joists. That's a recipe for noise and an uneven floor. – isherwood Jul 30 at 18:09
  • thanks wasn't aware, but also no frost concerns here in California – dabi Jul 30 at 18:27
  • @isherwood If I support the joists every 5' with 2x4 "shims" (distance from bottom of joist to concrete ground is never more than 3"), wouldn't that effectively change any span calculations? – dabi Jul 31 at 6:08
  • Sure, but like I said, it'll be noisy. Some of those shims will float due to imprecision and warpage, and when you walk on the deck they'll tap and crunch. A better plan would be to run one or two beams lengthwise and hang your joists on them with steel hangers. – isherwood Jul 31 at 12:33
  • You might also consider filling your patio and laying pavers. – isherwood Jul 31 at 12:33

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