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I am building a floating deck that is not attached to the house and is 2ft in height. The 4x4 posts are inserted into and resting on top of a concrete decking block. The post is just sitting inside the space provided in the block. In my area, Nevada, this is the only type of concrete deck block they sell. I have seen others where you can attach and secure the post to the block but no luck in my area.

First question, what is stopping any lateral force from pushing the deck over?

FYI, I have over engineered the base of the deck and it is solid. However, as you might guess, because the posts are not secured into the block in any way, I can actually lift the deck up and out of the blocks.

Could this be an issue (lifting the deck out of the blocks) and if so how could I correct it? (without tearing down and starting over)

A few points that might be raised:

  1. I did not want to dig holes for a concrete footer under each post. (Bad back, lots of work and I have seen many other decks built this way.)
  2. My assumption is that the fact that these blocks are manufactured this way, without a way to secure the post to the block, they can be used for this purpose.
  3. I do not live in a high wind, tornado or hurricane area.

Thanks

deck

Deck block and post

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  • You can glue the posts in with strong glue or drill and screw through them. The deck will likely be much harder to lift when complete with furniture on it. For that type of concrete I prefer a Drill/Driver with hammer drill function rather than an actual hammer drill to make a nice clean hole without cracking the block. That said, I can do it pretty much every time with a hammer drill too. – K H Apr 9 at 10:52
  • Glue is never to be considered a structural thing. It's for stiffness and sound prevention, but should be thought of as temporary. – isherwood Apr 9 at 14:19
  • @isherwood in this case, that and lack of need for a hammer drill would be part of the appeal for some. Unless you use a ton of glue it will transfer the weight of the block to the structure and still be reasonable to remove. Screws would do the same job better of course. That said, if you did want a permanent bond, with the right construction adhesive you can get a bond that outlasts the wood. It's just not the best option if you have a hammer drill. – K H Apr 11 at 11:00
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You could add a diagonal brace connecting each post to the joists - that would definitely eliminate any change of the posts folding under the deck.

My bigger concern is that your rim joists are load bearing. I'm not so concerned about the short front joist but if the back rim joist is only supported at both ends then you are putting a lot of weight on the center of that rim joist. At best your deck will be springy at worst at some future point the rim joist will collapse in the middle of a party. To solve this you could add a few more posts equally spaced along the rim joist and/or double up the rim joist. Given the small cost and ease I'd suggest both. If you do double up the back rim joist make sure they are well connected along the entire length so they really are supporting each other.

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  • Good point about the load-bearing rims... really they're "flush beams" and would usually be doubled (or larger members). I would double the joist, though. More posts are ugly and difficult to get aligned. – isherwood Apr 9 at 14:36
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Deck posts are no longer allowed to be attached with anchors alone in many areas. The joists should be resting on them. This solves two problems for you (without adding diagonal bracing) if you:

  • Notch the upper faces of the posts for at least half the thickness of the joist
  • Use through-bolts (usually galvanized or stainless 3/8" carriage bolts) to connect the joists to the posts in both directions (at least once through each joist--I might do two from one side and one in the middle from the other)

This eliminates any real concern of lateral movement for a couple reasons:

  • The combined stiffness of many posts will adequately stabilize the deck
  • The posts are very short, meaning that torque on the connections is minimal

Short of a tornado, lifting probably won't be a concern once all the decking is in place. It'll be heavy enough. If it's still a concern, screw-type RV anchors in a few hidden locations and connected to joists should do.

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