I am wanting to put up a 1.8m high (besser/cinder) block wall that spans 10 meters across our rear boundary. The wall will be tied to both other neighbours walls also.

The council water main runs 1.3 meters away from the boundary wall at a depth of 1.7 meters. This runs parallel to the new proposed block wall and trench.

What depth should the post holes go down to? I assume to the same depth?


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    Hello, and welcome to Stack Exchange. Why would you need post holes for a block wall? And, what is your climate (or where are you)? – Daniel Griscom Jan 31 '17 at 12:15
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    I would be hesitant to tie my new wall to my neighbors' old walls unless I knew that they were built at least as well as mine would be. – brhans Jan 31 '17 at 13:36

Concrete block walls don't have posts or piers, usually. They rest on a continuous footing. The depth of that footing can be found in established local code, and depends almost entirely on annual frost depth.

If your wall has support beams of concrete or steel you could build on piers, but that's a much more expensive and complicated approach. However, the depth requirement for either is probably the same.

| improve this answer | |
  • should have clarified - already have a 400 - 450 wide and 350 deep trench. Im in Sydney Australia so no frost. – chris Feb 1 '17 at 2:31
  • That doesn't clarify much. See the comments up yonder. – isherwood Feb 1 '17 at 2:52

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