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Based on this annotated image, can I reasonably pour concrete over the existing gravel in this carport area? If no, would it be enough to add another 1-2 inches of fresh gravel first?

Some details. I'm supposing a depth of 4 inches with wire reinforcement. Also, I would dig down about eight inches in an 18-24 inch wide "lip", with additional gravel and rebar reinforcement, where the concrete slopes down to the asphalt drive. The area to the right leading to the stairs would also be dug and graveled, just not as deep.

I've considered the drainage implications and I'm satisfied with the french drain on the right. However I'm thinking the channel drain is not necessary.. or if installed, should be pitched so the flow goes to the right and NOT the left as I have shown it. (oops)

Should I worry about catching and channeling water between the concrete and the brick surfaces where they meet...particularly on the left side where there is no eave to prevent precipitation from entering the carport?

enter image description here

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    Are you covering up weep holes in that brick wall?
    – Lee Sam
    Jun 13, 2017 at 4:56
  • Be sure to use control joints. I'd use one across the slab...to keep section sort-of square.
    – Lee Sam
    Jun 13, 2017 at 9:51
  • @LeeSam, are you referring to the isolated wall on the left? I'll have to look but I don't believe it has any. And would those be the baseball size holes sometimes found in retaining walls, or do you mean something else?
    – elrobis
    Jun 13, 2017 at 11:47
  • No, the wall on the right might have weep holes (usually just the size of a mortar joint).
    – Lee Sam
    Jun 13, 2017 at 16:16
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    @elrobis Yes, you want to keep the weep holes clear so moisture in the wall can drain. There won't be much, because the wall is protected with a roof, but wind blown rain could enter the brick veneer wall. (You can check to see if it's brick veneer or solid wythe brick by checking to see if there's a stud wall on the interior of the wall. If there is, then it's brick veneer.) I don't think you need a special channel to drain the weep holes. You'll only get a minor amount of moisture. But if it's not able to drain out (and evaporate) then it'll build up and rot the studs.
    – Lee Sam
    Jun 15, 2017 at 1:35

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Two things about an exterior concrete slab.

  1. Proper drainage. Pitch the slab slightly so the water drains away. 1/2" to 1" for 10' of run should be enough since it is covered.

  2. Proper compaction. Make sure the material under the slab is properly compacted. If you believe it needs more sand or gravel for better drainage or to level the area, then that added material has to be compacted before placing the concrete. Sand or road-gravel compacts better than loose stone. Undisturbed gravel with compacted sand for extra drainage or leveling would work great. Top soil makes a poor base since living matter can be compressed, so it is removed and made up with road-gravel or sand. Since you have a base that is not top soil and has been compacted by cars and settled for years you don't have that problem.

You have a well thought out design.

Good luck!

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