Deck Footing question above ground or no?

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Old 08-29-14, 09:41 AM
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Deck Footing question above ground or no?

About ready to submit my plans for a residential deck in NJ.

Code looks to be 22" footing diameter and 9" of thickness buried to 30". Everything I see recommends having the footings about 4" about grade.

Setting it up with a 22"x9" footing would leave me with 21" of buried post. I don't think this is optimal.

My questions is if I increase the footings to 34" (so that they are buried to 30" and I have 4" above grade) what is the acceptable diameter.. do I still need 22"?

Thanks in advance

First time diy decker - Rob
 
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Old 08-29-14, 09:46 AM
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If you want the deck to last without the posts rotting out, make the footings full-depth below frost line and extending 4" above grade. They'll be a lot thicker than 9", but concrete is cheap, and it never rots.
 
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Old 08-29-14, 09:51 AM
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Thanks for reply.. I am leaning that direction. You did not directly answer my question though... You are saying proceed with 22" diameter 34" thickness I believe?
 
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Old 08-29-14, 10:26 AM
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Your footing is a lot wider than your post needs to be - you would use a Sonotube on top of the footing and now we're talking 8 - 12" diameters.
 
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Old 08-29-14, 11:56 AM
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Without knowing your beam span and joist lengths, no one can tell you how large the footing diameters need to be, based on the requirements in DCA 6, Table 4. And if your soil is really substandard (mushy), Table 4 goes out the window, as it will require larger footing diameters for proper load distribution.
 
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Old 08-29-14, 03:29 PM
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Thanks I think I see it now.


The plan is for a 23' free standing deck that is too be an inch away from the back of my house. The deck will project out into my yard 25'. It will be 24" high. Plan as of now is 6x6 posts notched for double 2x10 beams. 2x8 joists. The beam span's are 9'10". The join span's are 10'6". 9 Posts and 3 beams.

My soil is fine, not mushy at all. Table 4 says I should be using a 22" diameter and a 9" thickness.

I spoke with the township building inspector and he said what he would do is dig the hole 22" diameter and 30" deep and then simply fill it with cement.

The sexier option seems to be placing a sonotube 9" off the bottom of the hole and then filling that to where I want it above the grade. Thus leaving a footing of 22" by 9" and then a cement pier that I will sink J bolts into.

Any thoughts?

Thank you so much for the help gentleman
 
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Old 08-29-14, 03:55 PM
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The second method with the sonotube is the norm - concrete isn't expensive but it's a PITA to have to make a lot more than you actually need.
 
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