Ask NADRA: Tilting Support Posts

February 3, 2012 |

My deck is supported by wood posts that rest on concrete piles set into the ground. The concrete piles seem to be moving causing a tilt to the wooden post (inward, toward the house). Do you have a guideline on how much post tilt is acceptable?

Glenn Mathewson, NADRA’s Technical Advisor, responds:

I can understand your concern and I’m glad you contacted NADRA for assistance. From what you have described, it does not reflect an appropriate foundation system. All foundations, including those for decks, must be placed a minimum of 12 inches below undisturbed soil. That refers to soil that has not been backfilled, rototilled, installed with sod, or any other disturbance. In a common yard the pier would be at least 18” below the top of the final grade. This depth provides lateral resistance to overturning… what your piers are likely doing. I presume insufficient depth of the piers is the source of this problem.

As for the posts, I can’t really recommend any acceptable tilt other than the tolerances in the bubble on a 4-foot level. I would presume that if the posts moved from vertical to tilted, then they’re likely to keep moving. That is a more significant issue than just a little angle on the post.

For the sake of discussion, a deck “could” be designed with a tremendous angle in the posts. For the sake of your deck, I would look at shoring it up and replacing the piers. If your posts are in good shape, you could even pour your piers a few inches higher than before; level the deck out nicely and then cut the posts back in at just the right height.

If your feeling up to it, grab a buddy or two, a weekend or two, and the right tools for the job, otherwise, take a look at our member directory and find a NADRA builder nearby. Either way… we wish you the best for you and your deck.

Thank you for contacting NADRA.

Glenn Mathewson
NADRA Technical Advisor

2 thoughts on “Ask NADRA: Tilting Support Posts”

  1. Great info! Further to it, is there a minimum deck height which would require the approx. 18′ (concrete?) foundations/piers? I have often seen decks built over a gently rear-sloping grade which are 12″ – 18″ above grade.

  2. just wanted to say what a great information site this is and to let you know that I have included your Check your Deck safety checklist on one of the sites we have. Great idea and a good tool for consumer awareness.

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