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Discussion Starter #1 (Edited)
Hello Everyone!

My Brother and I are building my deck and I have a quick question about the footers. I decided to go with concrete piers/footers to keep wooden posts out of the ground. I went to line up the piers and I discovered my main pier (that will bear the most weight) is pretty off-center from the footer, doh! I've attached a picture of this row of beams/piers/footers to get a visual.

The two footers on the left and right are 18" diameter x 12" tall, the middle is a 24" diameter x 16" tall. All buried 42" down to the frostline. All piers are 12" diameter. Is this off-center pier going to be a major issue? Should I try to weigh down the other (top) side of the footer with gravel or other hefty material? Any advice would be appreciated. Thanks!
 

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Civil Engineer
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I am a bit confused. You state that the two footers on the left and right are 18 inch diameter by 12 inches tall. The middle one is 24 inches in diameter and 16 inches tall. The "piers are 12 inch diameter". Are your piers concrete, and if so how are they attached to the footers? Was this a continuous pour, with the 12 inch piers placed using a 12 inch sonotube on top of a bigger cylinder?

Perhaps show us a side view of the footer/pier/post construction. And explain how you plan to attach the post, are you using a Simpson bracket?
 

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Discussion Starter #3 (Edited)
I am a bit confused. You state that the two footers on the left and right are 18 inch diameter by 12 inches tall. The middle one is 24 inches in diameter and 16 inches tall. The "piers are 12 inch diameter". Are your piers concrete, and if so how are they attached to the footers? Was this a continuous pour, with the 12 inch piers placed using a 12 inch sonotube on top of a bigger cylinder?

Perhaps show us a side view of the footer/pier/post construction. And explain how you plan to attach the post, are you using a Simpson bracket?
Yes all concrete, two separate pours for the footers and piers. I'm using rebar to keep them together. We dug the holes to code specification, hence the different diameters, filled the bottom of the holes with 12-16 inches of concrete to form the footer, then used 12 inch sonotube to bring the concrete to 2" above grade. The 6x6 posts will be attached with Simpson Strong Tie Post Bases.

My biggest concern was with how off-center the center pier was in regards to the footer. I've attached a front facing pic of the row in question. Thanks for your help!
 

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Civil Engineer
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The answer depends on whether you pulled a permit, and how strict your code official is. Typically code requires that "Posts shall be centered on footings." (Page 7, 2006 IRC). Note the use of the term footing, which of course in your case is buried underground, and not visible. So in practice, your post could be centered on the pier, however the pier might not be centered on the footer.

Does it matter in practice? If the soil is good, i.e. gravel, sandy, or glacial till, there will be no perceptible effect of an off center post. An off center post induces rotation on the footer, which definitely means that the allowable bearing capacity of the footer goes down, but your footer is 42 inches deep, and if the soil is good, the footer likely can hold much more than the deck load, so in this case is probably not an issue. This all changes if the soil is poor, i.e. soft clay, weak silt, or organic.
 

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Discussion Starter #5 (Edited)
Thanks for your input Daniel. The soil is clay unfortunately. But the inspector/code called for a 22" diameter footer by 8" height. I over compensated just to be safe and went with a 24" diameter by 16" height. Partly because the closest auger bit I could find to 22" was a 24".

When I got home tonight I looked again and the pier isn't as off-center as I depicted earlier. It's about 4" from the closest edge and 8" from the other. Plus I plan to backfill the hole (on top of the footer) with large chunks of rock I excavated from digging and fill with sand to secure the footer as much as possible. Though I'm not sure sand is so good around clay, unless there's a better option?

I honestly think I'm over-worrying about this, but I wanted to get some extra insight. Thanks again!
 
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