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I am planning on building a raised concrete patio. I would like to build the perimeter of block and fill it with stone and then cap it in concrete to be finished with blue stone later. The patio will be about 3 ft off the ground and jogs in and out but basically 40 ft long and about 12 ft wide.

I plan to hook #2 re bar into the top of the block and fill the blocks with concrete. Is the stone fill enough support for the concrete ? If not how far can I span it before I need another block wall for support.

I built a home once that had a 10 ft x 10 ft sun room filled with stone from the basement footings to the main floor and capped in concrete. It seemed to work well. Does anyone see a problem with this?

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FWIW, that's technically called a "raised patio" rather than a deck. At 40' long, your challenge will be to prevent cracking...so I'd count on putting in expansion joints.

If you want to ensure a solid base, you need to use crushed rock and add it layer-by-layer mechanically compacting each layer before adding the next. That's going to be some work to get up to 12", but certainly doable. You'll likely raise it in 3-4 layers.

At that point, you're essentially building a slab-on-grade foundation. So you shouldn't need any actual foundation walls.

All that said, check with local code first!

Note, however, that if you're ultimately capping with stone, you really don't need all that concrete on top. You need a retaining wall to retain the layers of compacted rock, but you can then place the stone right on top of that on top of a layer of sand.

  • Thank's for the answer. That will save me a lot of concrete. – Tom G. Mar 2 '16 at 12:30
  • What size of stone or crushed rock should I use ? – Tom G. Mar 2 '16 at 12:31
  • 3/4" is typical, but ask your local landscape supplier for what is best available in your area. – DA01 Mar 2 '16 at 14:29
  • I have seen similar patios done with a few deep footers. Do you think he doesn't need this? – DMoore Mar 2 '16 at 18:21
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Sorry, I have to disagree here.

First of all, this is not a raised patio. This is not just a retaining wall with stone in it. The fact that you want to have 4 ft vertical block walls changes everything when compared to a sloped soil pad with a concrete pad on top. Is this up against a building (thats the definition of a deck versus a patio)?

A deck structure this size will need tiebacks, footings, drainage etc. not to mention be designed and built correctly. Even the slightest bit of water permeation into the fill could result in ice blowout if you are in a cold area. This sounds like a perfect example of just enough knowledge to be dangerous. Find a designer, engineer or architect to look at this for you.

  • It is going to be a deck built with footings and 8in block around the entire perimeter so it will be free standing. It is up against a manufactured home but the only part where it will meet the home is at the finished stone top. I plan to use reinforcement wire every other course. I will fill the block with concrete and shove re bar down into it. It is max only 4ft high. I can add tie backs if you feel it is needed. Drainage is not a problem but I could install drain tile. The job is in Arizona and footings can be poured 8 inches deep by code. – Tom G. Mar 2 '16 at 15:40
  • At 4ft high it sounds over-engineered to me. Not a criticism, I am pointing out that it seems safe enough to me that I don't see the need to get an engineer involved. I should caution that though I am a chartered engineer, I have no professional experience in masonry or in retaining walls, though I have a basic understanding of them. – AndyT Mar 2 '16 at 16:24
  • I would agree. I will file the plan that I sketch to the county building dept. So if there is a problem they won't issue a permit. I have a sketch that I will post as soon as I figure out how to attach it to this response. – Tom G. Mar 2 '16 at 16:38
  • Did I miss the 4' high part in the question? Oh...I did! I totally agree here. 3' is pretty high and likely deserves some engineering. That said, 3' is an ok height for retaining walls and should hold the patio just fine. – DA01 Mar 2 '16 at 20:11
  • If you do go this route I'd a) treat the perimeter as a retaining wall using retaining wall blocks (instead of cinder blocks) b) consult an engineer – DA01 Mar 2 '16 at 20:15

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