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I am looking to build footings for three 6"x6" patio cover posts which will support a 6"x8"x19ft beam for a 19ft wide x 16ft deep patio cover that will fix to my house using a ledger board. We have an existing 4" concrete slab. Looking at the cleanest option/smallest opening for concrete footers that will support these beams. Anchoring the bases of the posts using red head anchors. My area calls for a 14" wide x 14" long x 12" deep footing for the post.

Should I cut out a 14 x 14" square in the concrete to dig a hole below it to fill with concrete? Can I cut a smaller hole but dig deeper to use a concrete tube?

Appreciate any guidance.

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  • What area are you in? You might want to check, ask, the local building authority.
    – JACK
    Jul 20, 2020 at 19:20
  • You can always go deeper but the area of the footing is important because you don’t want it to sink. Cutting a square is regularly done.
    – Ed Beal
    Jul 20, 2020 at 20:01
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    I am a DIY'r but standard practice with this is new to me. Thanks for the insight on the square hole. It's funny that I've seen folk's covers but never paid attention to the footers of the posts.
    – Hans
    Jul 20, 2020 at 20:08

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Cleanest is probably to use a core drill to cut a hole for the post and then use a vacuum excavator to dig the hole. Neither step is particularly DIY

If you drill a 6" hole and then use a angle grinder with a concrete blade to enlarge it to 6" square that might be slightly neater than the 9" hole you'd otherwise need.

If there are no lateral loads on the post, you may be able to just bolt it the surface of the concrete using a post bracket

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  • It's really slow but I've used a shop vac with a dust deputy on it. Hand digging or disturbing the soil with compressed air and vacuuming it out. Slow and time consuming but able to be done without major equipment like a vac trailer. You can rent a vac trailer if you want things done quickly.
    – Dano0430
    Oct 13, 2021 at 14:09
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Your question seems to be simply whether you can bell out the hole for the footing. Yes, you can. Footing specifications are for the footing structure itself, not where or how you access the space occupied by the footing. The opening in the patio would only need to be large enough for concrete to pass through, but obviously you'll need to get a post-hole digger or other tool in there as well.

You might get better answers and suggestions if updated your question post with some information about your project. Narrowly-scoped questions like this aren't terribly helpful to you or the community.

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  • Thanks for this information. I've added some info that I hope sheds light.
    – Hans
    Jul 20, 2020 at 20:00
  • Personally, I wouldn't bell the footing hole under an existing slab. Normally I would but if there is any heave to the footing wouldn't you risk damage to the slab?
    – Dano0430
    Oct 13, 2021 at 14:10
  • The whole point of frost footings is to completely eliminate heave. If you get heave, you didn't build frost footings.
    – isherwood
    Oct 13, 2021 at 14:13

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