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Deck Foundation Sizing Survey

That's what has worried me in the past, not settlement but a slender poorly footed pier to grade on solid ground with loose fill around its' tube and an eccentric post placement at the hinge between pier and post. I try to talk clients into running the posts down to the footing to avoid that hinge and potential lateral problem. I noticed in Papio's version that this is prohibited and am curious about the reasoning. BTW it is showing the ledger lags above the joist hangers, tension perp failure, I've seen pics of that deck on the ground with lags and the top of the ledger still on the building.

Those of you requiring a larger diameter pier, is it for footing size or lateral resistance?
 
So Pap you do not deduct the weight of the footing as dead load ? and there is NO safety factor in your analysis at all?

The friction thing only works in friction piles not in shovel applied backfil as well

you are giving a gift at those areas and weights
 
Not to be a pesemist but you are trying to teach a rock to sing. All your honorable work will only keep honest people honest and smart people smart. unfortunatly stupid abounds, and ya can't fix legislate or change stupid; you can only dis-approve upon inspection.
 
Standard practice in my area is a 8" diameter hole, 42" deep filled with concrete with post anchored to top. Soil conditions range from sand to clay. I have yet to see any pier footing of this design fail in any way. If this type of BS finds a way into the 2015 IRC/IBC it will only be another reason for jurisdictions to NOT adopt yet another code cycle.
 
Papio, your deck format is one of the better ones I've seen, going to tweak & utilize that as a templete.

Clarification- Using a 6 by post = we have allowed 12" diameter... We allow this when the deck is low to the ground and capable of utilizing a 4 by.

One item we make abundently clear to applicants on submission, if they can center every pier with the post connection then they are welcome to utilize the minimum sizes but if the pier to post connection is even slightly offset they must step up the size appropriately.

DRP & Architect1281 bring another question to mind, primarily in our area we see augered holes without the use of sonotubes, what method are you seeing in your area?

Contractors in my area are reluctant to countersink posts into piers due to snapping at the top of the pier. Now correct me if I am wrong but wouldn't the introducation of countersinking the posts eliminate the necessity of lateral tension devices?
 
Keystone said:
Now correct me if I am wrong but wouldn't the introducation of countersinking the posts eliminate the necessity of lateral tension devices?
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It can.

I researched this, and found a formula in the IBC that has been there for decades for freestanding signs. I wrote an article about this in the Professional Deck Builder. I also put together a table of embedment/# of posts/height combinations that would yield 3,000 lbs of lateral resistance.

Have a read. The part about sinking posts is on the third page. I think you will find it interesting.

Handling Lateral Loads - Building Science, Structure, Design, Framing - Professional Deck Builder Magazine Page 1 of 3
 
Jus a little tool I use when teaching Deck / residential plan review Note NO SAFETY FACTORS APPLIED

Footing / Pier Soil PSF/area TOTAL LOAD LBS

dia Area DL conc 1500 2000 3000

Sq.Ft. Lbs. Total Net Total Net Total Net

8 0.349 209.33 523.33 314.00 697.78 488.44 1046.67 837.33

10 0.545 272.57 817.71 545.14 1090.28 817.71 1635.42 1362.85

12 0.785 392.50 1177.50 785.00 1570.00 1177.50 2355.00 1962.50

16 1.396 697.78 2093.33 1395.56 2791.11 2093.33 4186.67 3488.89

Dia Live Load Tributary Deck area in SF per pier at Live Load + 10 DL

8 40 6.28 9.77 16.75

10 40 10.90 16.35 27.26

12 40 15.70 23.55 39.25

16 40 27.91 41.87 69.78

8 50 5.23 8.14 13.96

10 50 9.09 13.63 22.71

12 50 13.08 19.63 32.71

16 50 23.26 34.89 58.15

8 60 4.49 6.98 11.96

10 60 7.79 11.68 19.47

12 60 11.21 16.82 28.04

16 60 19.94 29.90 49.84
 
I think that it should be viewed as a footer period. What ever the requirements are for house pier footer, the deck footer should meet. It should be that way so that in the future a roof can be added and the footer will still be adequate. Otherwise, you will have minimal footers can't handle the additional load that the home owner puts on it when he builds his roof without a permit, or adds a second level deck to it.

I've worked in areas that required 6"s of concrete under a post for a deck and 8"s if its a covered deck, and of course the other areas out in the wild Tennessee county side where there isn't any inspections or permits required for decks
 
Architect1281 said:
Yes lateral loads are reduced or eliminated by adequate embedment; next issue wood posts must then be rated for direct burial and not ground or above contact.
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I haven't seen any treated 4x4s or 6x6s that were not rated for direct burial.
 
Thank you all for the responses. They will provide a great perspective and pulse of what is really going on out there, before any changes to it are proposed. I only wish I had more time to keep collecting data. Plenty of time for the 2018 edition...but running out for the 2015.

Know where you are, before you decide where you're going.
 
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