I am doing the design of a deck footing and in many places where I read it says that the footing (sonotube) should be set with the top end terminated 2" above the ground level

In my case I am building on top of a patio and I need to understand why 2" and if those 2" must be above soil level (which is way below the three layers -gravel, crushed stone and bricks-that build my patio) or just above the patio level

Please have a look at the diagram below and tell me which case is recommended and why

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Update:The recommendation regarding the 2" comes from this book step 5 on that page

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    I don't want to post this as an answer because I'm guessing but I believe it's to ensure that the concrete stays above ground - meaning soil - to help prevent water pooling on top of the post which could speed up deterioration of any mounted posts. IN your case with the gravel/stone bed you're going around I think you will be fine with C or even with "D" - top of the tube at gravel level – The Evil Greebo Jul 3 '17 at 14:24
  • I might consider D if I completely want to mask the post holder which aesthetically is OK but practically puts the piece of metal into the crushed stone which holds humidity and that post holder might end up rusting faster then I would like – MiniMe Jul 3 '17 at 15:19
  • Fair enough - in any case I think you'll be absolutely fine with C where the brick comes up to the post – The Evil Greebo Jul 3 '17 at 15:42
  • I am inclined toward that one too – MiniMe Jul 3 '17 at 15:43
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    I vote A. The top of the sonotube the concrete should be able to dry/wick. It is the concrete that would disintegrate with constant contact with water. This is completely below a deck? The deck...at least 15" high. Same elevation with the interior of the home? Case C is a big no no with your pavers right up to the post, too much moisture held by the wood too long... – stormy Jul 5 '17 at 23:41

"C" is the way to go - it has cleanest look. The point of raising the concrete is to prevent the end grain from wicking moisture and rotting - the concrete is NOT going to deteriorate (unless its mixed poorly and not allowed to cure correctly). Generally, you don't want wood engaging the ground, nor do you want it sitting directly on concrete. We separate sill plates all around building foundation walls with foam because the sills will wick from the concrete and rot. Raising the concrete is not the only way to solve the problem... take preventative steps to limit/reduce/stop water from wicking. Raise the bottom of the wood so it doesn't sit directly on the concrete. https://www.strongtie.com/capsandbases_woodconnectors/category

We put fences in the ground all the time. They don't rot (because preventative measures are taken), or do so over an extended period of time. We don't want the column rotting, but we aren't sticking it in the ground either. Your detail shows it sitting flush with crushed gravel. I would dip the end in post preservative or better yet coat it with tar. I'd use a simpson product to keep it off of the concrete (I like the stand off post bases), but keep it below the paver.

  • I ended up implementing that + one of these vuetrade.com/product/… so it is the footing in the ground, the support bolted to the footing and then the wood post. Practically my deck floats about the patio because it has wood skirts that block the view and you barely see metal supports :-) A very unorthodox deck ...all in all – MiniMe Feb 20 '18 at 20:14
  • That's a very cool looking product - i look forward to trying it out. Deck sounds very cool - glad it all worked out. – Skinner Feb 20 '18 at 23:14

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