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I am building a deck between my house and the garage. I will support the deck on one side with a ledger on the house and plan to support the other side with a ledger on the garage (with requisite beams in between).

My question is whether or not it is recommended to attach a ledger to the concrete pad that the detached garage is built on. The pad appears to be approx 5" thick (at least on the edges) and either a 2" x 8" or 2" x 6" ledger would hang below the bottom edge of the concrete pad (assuming I would like at least 2 inches above the ledger for decking and gap).

Does anyone have any recommendations for this? Thanks.

  • Trying to envision this but am missing something, there is no stemwall, turned down slab, thickened edge, or any other type of additional support for the slab? Is the entire edge of the slab exposed? Will the deck be buried in the ground? – Damon Jul 22 '15 at 3:49
  • I'm not well versed with how concrete slabs are poured for detached garages. There may very well be additional support. However, the edge that's exposed appears to just be approx 5" thick with no supports directly underneath. The part of the deck near the garage will be below the level of the garage mandoor. I'm moving earth around and will backfill with gravel. The other level of the deck will be approx 16" above grade. – fideli Jul 22 '15 at 4:29
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You want to attach the ledger to the edge of a concrete pad? Sounds like a terrible idea to me.

It's possible that an engineer could have designed a way to carry the load through the pad and into the ground, but that would have to have been done before pouring the pad. Attaching the ledger to an existing pad, will almost certainly crack, split, or otherwise damage the pad. Which will lead to the ledger losing any structural integrity that it had.

A better idea would to support the deck with posts, so that side of the deck "floats" up near the pad. You'll want to avoid direct contact between the deck and the pad, so you'll leave a small gap between them.

  • thanks for the prompt answer. Looks like I'll be adding an additional beam close to the garage, then. – fideli Jul 22 '15 at 4:24
  • Agree with @Tester101. Self support the deck as if the garage was not there. The bigger problem is tying the deck to the garage as it will want to move over time (a long time if done properly). Maybe you can drill the concrete in the middle and pin the ledger to the slab into the holes with long small diameter anchors (redhead or equivalent, NOT a blue tapcon) with a stack of galvanized washers between the ledger and the slab to keep a gap between the ledger and the slab. If you stay in the middle of the slab, you should be OK. – Damon Jul 22 '15 at 4:40
  • @Damon The deck will have downward forces on it, which means any fastener that goes into the concrete will have upward forces at the tip in the concrete (think seesaw). Concrete is not meant to handle these types of forces, and will be damaged over time. I'm no engineer, but I can't think of a safe way to attach to an existing pad. – Tester101 Jul 22 '15 at 12:58
  • Just curious, how would the forces differ for a ledger installed on a concrete foundation for a house? In that case, assume that the house has a basement. From my research, attaching a ledger to a concrete house foundation is commonly done. – fideli Jul 22 '15 at 16:58
  • @fideli The forces are not different, but a foundation is much different than a concrete pad. – Tester101 Jul 22 '15 at 18:24

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