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Footings for my deck must be dug at least 48" deep to be below the frost line and meet code. I will be using 12" x 48" sonotubes for a combined pier and footing. I have an auger with a 12" bit for drilling the hole.

I would like the top of the pier to be a few inches above ground level to help avoid snow. Something like a 52" sonotube would be perfect but alas I cannot find 5' or 6' foot tubes in my area. There are 12' tubes but I can only get two 52" tubes out of that with a remainder of one 42" tube which would go to waste.

  1. How can I splice/tape/join two 12" diameter sonotubes together to increase the length of the tube?
  2. Which end should be at the bottom vs. the top?
  3. How do I ensure it all remains level?

I plan to backfill the dug hole before pouring the concrete in.

Or should I simply place the sonotube to the desired level and let the bottom fill in with the extra concrete? In this case I wouldn't be able to backfill the hole which might make placement more difficult.

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    For just a few inches, make a wooden form at the bottom and place the tube on top. 2x6s will give 5.5 inch rise.
    – crip659
    Commented Aug 5, 2023 at 18:21
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    I'll let someone with actual experience of this answer, but I'd put 3 slices, about 4" long into the tube that's going into the other. 3 drywall screws to pin it and you're done.
    – Aloysius Defenestrate
    Commented Aug 5, 2023 at 19:29
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    I'd give careful consideration to the cost of having a form blow out when pouring and "waste" the extra length from the 12 foot tubes you can get. Concrete is heavy and can be quite uncooperative if you give it an opportunity to find a weak spot. Either that or pour a footing with rebar sticking out that lets you pour the desired column height with a 48" tube, later.
    – Ecnerwal
    Commented Aug 5, 2023 at 19:59
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    Does your code require the sonotubes? If you dig the hole to 48" then just cut about 4 inches out of a tube. Add 3 or 4 2x4 s about 12" long, screwed into the outside of the tube about an inch from one end. when you have the hole almost filled with the concrete add the 4 inches of tube over the hole and pour the concrete to the top of the tube. If you added a couple of rebars to each hole you will be good. The concrete being a singe pour per pier will be very strong and above the ground. Want it to be higher? Cut more out of a tube. Get 16 4" pieces from a 48" tube
    – RMDman
    Commented Aug 6, 2023 at 0:00
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    @RMDman the only info I got out of our code enforcement officer was to dig 48" to be below the frost line. Our small town does not have a code book or guidelines.
    – Ryan Taylor
    Commented Aug 6, 2023 at 1:15

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Pouring concrete directly into the drilled hole without a sonotube lining it, is typically how it is done. The sonotube is simply a handy way to get a nice looking pour above grade.

If you are planning on putting the sonotube any kind of depth in the bored hole, the deeper you go with the tube, the more accurate you will need to drill the hole, since both are going to be pretty much the same size. If you cut a 12" piece and set that in the hole 6 or 7" and support it at the height you want above grade with a few 2X or even 1X screwed from the inside of the tube will help keep it in place. Run the wood long enough so a few wood stakes can be driven in to hold it steady without caving dirt into the footing. 3' pieces 1X or 2X should do it. That would hopefully get the stakes about 1' away from the footing.

This might be something that is good to know. Not all the tubes are 12" inside, some smaller, some may be larger. This is done so the "12 inch" tubes can be shipped without taking up so much room. The same goes for the other sizes too.

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  • Could just drill a couple holes in the sonotube through the diameter X inches below the top, then run a length of rebar or other similar stake, and set the tube in the hole. The rebar will keep the X inches of tube sitting above the ground level. The rebar won't keep the concrete from being thrown in the tube, and can be removed once the concrete is close to the rebar level, then filled up the rest of the way.
    – Huesmann
    Commented Aug 6, 2023 at 16:42

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