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Carport retaining wall

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  • Carport retaining wall

    I'm wanting to build a concrete slab carport on a piece of sloping ground. To make it level two sides would need to be a retaining wall of height between 0 and 700mm. I understand that the carport is regarded as surcharge, as are the vehicles. But is concrete? Can I concrete to the edge if it is not possible for a vehicle to put weight within 700mm of the edge? What would happen if I poured concrete behind the retaining wall instead of rock, during the slab pour? Would it be regarded as an elevated slab instead of a retaining wall? I'm trying to avoid consent. I know I can move the walls out to avoid the surcharge but I'd prefer not to

  • #2
    I agree with you that this is not a retaining wall

    you could also builkd a wooden cardeck

    put a hi bond floor in and save yourself the trouble of compacting fill
    Last edited by John the builder; 09-10-2020, 12:38 PM. Reason: hibopnd option


    • #3
      Still sounds like an engineered structure to me, requiring a footing, "wall" and pad, all reinforced and tied together. Add in the engineer, consent, inspections and I can see why you can to avoid it.


      • #4
        perhaps it needs engineering
        but the carport doesn't need consent and the platform can be built as a concrete or timber (car)deck if under 1.5m high, The wall isnt a retaining wall if tied to the slab.

        Can be built without consent but be careful you dont breach a planning rule (but if you did you could get retrospective resource consent later?
        Last edited by John the builder; 12-10-2020, 09:54 AM.


        • #5
          Hey there,
          Structural Engineer here. Car on top of retaining wall is a surcharge. You would get away with a concrete path, but a full driveway implies cars so you're back to the surcharge case.
          Walls under 1.5m don't require Building Consent unless they're surcharged (driveway, building, backslope).

          The question you have to ask yourself is will the Council determine it is surcharge (or will they even take notice). If you use the document I reference below to construct the wall at least it will comply with the Building Code so you can always do a Certificate of Acceptance if it became a problem. Take photos .

          FYI I would probably do it for Zone 3 and Soils A & C as that is the worse case. You can tie your driveway into the top too if you like. Make sure your foundation is on competent ground, not a swamp!

          I cant post links but Google NZS4229 and look for the Standards NZ link. Page 130 is the goer for this situation (car on top). That standard is the manual for ready to build designs.

          Have fun.


          • #6
            do you accept that the wall doesnt have to be a retaining wall or considered one ' and if a deck the surcharge restriction doesnt apply?

            your fig A2 doesnt have a concrete slab?
            Last edited by John the builder; 15-10-2020, 12:52 PM.


            • #7
              Originally posted by John the builder View Post
              do you accept that the wall doesnt have to be a retaining wall or considered one ' and if a deck the surcharge restriction doesnt apply?

              your fig A2 doesnt have a concrete slab?
              Sorry I can't post links :/, have a Google of 'Building Code 13.2' and look at this information there. They are fundamentally retaining walls but don't require consent.

              Yeah and it only lists a 2.5kPa surcharge. About time for an update there. Those details in that standard are taken from another place called the 'Masonry Manual'. Perhaps give that one a look over. Search 'Masonry Manual 6.1' and have look through some of those examples, there's quite a few in there.


              • #8
                It looks like I can construct as per figure 6.5a. The problem with B1.1 is that the conditions state it must be freestanding, and this would not as it would be tied to the driveway. But considering the rebar, membrane and concrete required, it looks easier to move the wall out further, away from the surcharge, where the only requirement is a drainage pipe

                Thanks to you both


                • #9
                  your call

                  but making so much of a 700 high wall is complicating things isnt it?

                  It is not a retaining wall (if tied to the slab or there is no fill (Hibond option) it is a platform) and exempt from consent