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My wife and I would like to build a 6 foot high, 8 foot long fountain wall, using concrete cinder block that will then be covered with stone veneer.

My question is regarding the footing. We obviously don't want it to fall over.

Our yard is expansive clay soil.

How large and deep does our footing need to be? Would something like 2 foot wide and 12 inches deep be sufficient for this purpose?

And how far underground should the footing be buried?

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  • Where are you located ? (for frost line). Will the wall be a freestanding wall or a retaining wall? Are you located in a high wind area or seismic active area? – Lee Sam Sep 26 '20 at 20:17
  • will this wall have any lateral force against it? For example will it be back filled with soil on either side? Are you planning to fill block cells with concrete or cement? – plumb bob Sep 26 '20 at 20:19
  • is the wall straight or curved? – Jasen Sep 27 '20 at 2:02
  • @Lee Sam - We are located in the San Francisco East Bay Area, and yes, we are in an earthquake zone. The wall will be free standing, with no backfill. I'm not sure what high winds mean. Certainly no hurricanes or tornadoes, but a 60 MPH wind could happen once every few years. – Jimmy Sep 27 '20 at 6:43
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    @plumb bob - No backfill, it's a freestanding wall. I was planning to create 3 vertical columns of cement inside the block wall, and reinforce with rebar. Would also add a bond beam on the top row. – Jimmy Sep 27 '20 at 6:47
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To answer your question, the bottom of your footing needs to be a minimum of 12” below finish grade, where you live. However, I feel you don’t understand the complexity of this project so I’m going to layout a few issues you’ll need to resolve.

First, this wall will weigh about 4,800 lbs. (plus weight of your stone veneer) so if it falls over it’s a dangerous big deal. (The footing will weigh an additional 7,200 lbs.)

Also, you want to know the size of the footing, which is going to be approximately 6-8’ wide x 12” deep with a “ton” of rebar in it.

You call your soil “expansive clay”, which is extremely difficult to design stable footings in it AND may require the footing to be 2-3’ deep (which will increase the weight of the wall by an additional 2,400 lbs.)

You say wind loads could reach 60 mph, but my experience is you’ll have 120 mph gusts every year.

However, you live in a high seismic zone so special consideration should be designed for the connection between the wall and the footing.

I strongly suggest you have a structural engineer (not civil engineer) or architect help you with the design.

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  • When Lee mentions 120MPH gusts, that might sound like hyperbole, but it's not. Search online for the ASCE 7 Wind Load Map and you'll notice San Francisco is in a 85 MPH wind zone. That's actually the lowest in the country. In Florida, some areas are 180 MPH. Puerto Rico is 145 MPH (and that probably should be raised for all of PR.) – Jeff Wheeler Sep 27 '20 at 18:41
  • I think you've just convinced us not to build this. We just wanted a cute fountain in the backyard, and didn't anticipate we would need a structural engineer and 12,000 lbs of concrete. – Jimmy Sep 27 '20 at 21:54
  • If there was a brace at the top of the wall, it would be easier to design and to build. – Lee Sam Sep 27 '20 at 22:44
  • Yes, makes sense. Like if there were a 90 degree bend in the wall? – Jimmy Sep 28 '20 at 15:18

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