Interior Footing Embedment

• Mar 17, 2014

• #2

dcarr82775

Structural

Jun 1, 2009

1,045

IRC Section R403.1.4 has almost the same language.

 

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• Mar 18, 2014

• #3

nac521

Structural

May 11, 2011

55

If by embedment, you mean footing thickness, then IRC403.1.1 states 6" thickness minimum. Chapter 7 of ACI 332-10 also covers residential applications for concrete footings and states similar requirements.

 

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• Mar 18, 2014

• #4

jayrod12

Structural

Mar 8, 2011

6,277

and if you're talking about being keyed into the native soil then I don't know of a minimum embedment. If you are requiring the pad to take lateral load then there's more issues. Especially in residential.

 

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• Mar 18, 2014

• #5

AELLC

Structural

Mar 4, 2011

1,339

It is more of the Geotech's call because you can get a bearing failure if the surrounding soil can heave the slab upward.

12" would be absolute minimum. I would not ever allow 6" thickness in any residential ftg, 12" is minimum for pad ftgs, and 8" is min for wall ftgs.

Here in Phoenix, despite no frost, it is actually 18" minimum embedment req'd

 

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• Mar 18, 2014

• #6

AELLC

Structural

Mar 4, 2011

1,339

ps

I meant 8" thick wall ftg with 4" ext grade cover, but here in PHX we need that wall ftg to be embedded at least 18" BELOW top of ext grade.

 

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• Mar 18, 2014

• #7

jayrod12

Structural

Mar 8, 2011

6,277

Maybe I read the question wrong, but I believe he was asking about interior footing/pads, therefore zero frost concerns. you can place the footing directly below the main floor/basement slab and it shouldn't matter.

 

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• Mar 18, 2014

• #8

AELLC

Structural

Mar 4, 2011

1,339

If you disregard frost, then you need at least 12" embedment (read bearing depth) anyway.

Or 18" here in PHX.

 

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• Mar 18, 2014

• #9

jayrod12

Structural

Mar 8, 2011

6,277

I come from an area where basements, or at least crawlspaces are the norm because we already have to go to at least 6 feet for frost on the exterior anyway so I've never been concerned about interior pads.

 

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• Mar 18, 2014

• #10

msquared48

Structural

Aug 7, 2007

14,745

I high seismic areas such as where I am, we are concerned with the interior footings literally walking laterally under seismic action, so we always embed the footings at least 7" to prevent lateral movement and loss of support of the column/beam structure above. 12" would be good.

Mike McCann
MMC Engineering

 

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• Mar 18, 2014

• #11

IsaacStructural

Structural

Dec 1, 2010

172

Here we drop exterior footings 42" for frost, and commonly place the top of interior footings directly below the slab on grade and provide a diamond control pattern at the column itself. Depth to bottom (bearing) of the footing depends on the footing thickness, but won't ever be less than 12".

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

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