We are considering adding a deck to the top of our flat roof detached garage, if the necessary work involved is reasonable. The garage is 20' deep x 28' wide separated into 3 bays, the widest of which is 12'.

The current framing on the two interior walls is a conventional double top plate on top of 2x4 studs 16" oc, supporting 2x6 joists. The exterior walls however have a 1x8 ribbon/ledger let in to support the joists. Presumably this was done to support the parapet, and could end up being convenient if we can attach railing to.

Is the ribbon sufficient to support the live deck loads? Based on the span, I think 2x8 joists would be enough, and these could be fit by notching the ends to rest on the existing ribbon and top plate.

If the ribbon isn't enough, are there any straightforward ways of retrofitting a stronger wall system?

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  • Can you clarify that you intend to put the deck on top of the garage? – Michael Karas Feb 13 '18 at 4:10
  • Yes, a roof deck over the garage. Edited the question, thanks. – Kdubya Feb 13 '18 at 4:26
  • So the span across each bay is about 9 feet each? – Lee Sam Feb 13 '18 at 5:58
  • Lee, the span varies. 10ft is the first, 11.5 in the middle, and 6.5 on the last. Ok, so the last isn't really a bay, but hopefully you get the idea.. – Kdubya Feb 13 '18 at 6:04

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