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Outdoor Fireplace Foundation Question

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  • Outdoor Fireplace Foundation Question

    Hi all,
    First off thanks for building such a great resource, I've read through several other similar situations as the one I'm outlining below but felt the need to start a thread to get some opinions and hard feedback.

    We're looking to build a 12 foot high outdoor fireplace from cinder block/veneer stone. The fireplace will be approximately 4 feet by 10 feet.

    We have about 12 inches of compacted gravel as a base ontop of which we poured a ~6 inch thick cement pad. The pad is heavily reinforced with rebar.

    We're located in the Chicago area, and after pouring it started to have some second thoughts and concerns about ground movement/freeze thaw cycles.

    As we see it, we have two options given we already have the slab in place:

    1) Leave it as is and build, while installing a french drain all around the slab to help divert any excess water to hopefully prevent any major ground movement.

    2) Underdig each side of the slab one side at a time to 42-48 inches deep and place a traditional foundation wall under each of the 4 sides of the slab to help support it and prevent ground movement.

    At this stage we are really not looking to break up 5,000 pounds of concrete, so I would love to hear from others who have actually built something similar in the past as to what their long term experience has been. We certainly don't want to embark on a 3-4 month build without having a very solid foundation that will last.

    Thanks in advance and look forward to hear everyone's thoughts/feedback!