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How to construct Footers For Foundation

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  • How to construct Footers For Foundation

    Uno (and others):

    Long story short, I've decided to build a new foundation next to my patio, mainly for the space issues - (see my "Foundation Thickness" thread if interested). What is the best way to build? I don't want to over build for a nuclear war due to budget but enough so I don't need to worry about frost heave/the oven sliding down my hill. I know my foundation will be 6-8 inches thick with rebar but my questions mainly involve the footers.

    Assuming footers are 30+ inches deep with gravel at base - how wide should the footers be?

    Do I have to build one continuous footer (like a box) or can a put in sono tubes on each corner (4 total?) (like a table)/what width?

    Is this a two part pour using rebar to tie the footers/foundation together or do I pour the footers/foundation separate - still tying together I'm assuming?

    Pretty handy but never done work like this before. Should I call in the professionals or can I tackle myself.

    Again thanks in advance for everyone's helps/suggestions.
    Dick

    Once I get this done I can concentrate on my actual oven project next spring!!!!

  • #2
    Re: How to construct Footers For Foundation

    For a free-standing oven that doesn't have an extremely high masonry chimney, you may not need footings at all, if the support slab has a well drained layer of crushed stone under it. If you do footers, they should be substantial, and wider than wall it supports, and well below the frost line. I did three feet here in New Jersey, and Ohio is colder than the east coast. I'm no engineer, but I would think that four 30 inch deep sonotubes at each corner of the slab would just give the frost heave something to grab on to.

    If you are not alergic to hard work, there is no reason not to do this yourself, particularly if you have a helper or two. Calling in a ready-mix truck is a good work-and-time saver, and cost effective. Hiring masons will cost you serious money.
    My geodesic oven project: part 1, part 2

    Comment


    • #3
      Re: How to construct Footers For Foundation

      Dmum

      Thanks. Sorry, just to clarify would the sonotubes work? Not sure if "sonotubes at each corner of the slab would just give the frost heave something to grab on to" is a good thing or a bad thing...?

      Also, I was planning on a 10 foot (due to the pergola) duravent - not an extensive masonry chimney.

      I'm definitely going 30 inches. Part of the reason for the new foundation was lack of appropriate footers (Uno provided a fix) but like I said I've decided to build a new footer/foundation next to the current patio.

      Thanks
      Dick

      Comment


      • #4
        Re: How to construct Footers For Foundation

        Here's how Frost Heave works. When certain soils freeze, they form a structure called an "ice lens". I don't entirely understand it, but these continue to expand in a unidirectional way by drawing water from the unfrozen soil below, and the force pushes solid objects like rocks and foundations upward to the surface of the soil. A solid footing needs two things, to be well below the frost line, and to have a bigger base than the wall it supports. Building code for fireplaces call for footing twelve inches thick, extending six inches beyond the exterior walls.

        By putting in sonotubes of concrete, you may just be building artificial boulders for the frost heave to push.

        There is a new movement for avoiding footings below the frost line entirely, using insulated shallow footings. There are different methods for heated buildings like houses, and unheated buildings like garages. Instead of deep footers being built on undisturbed subsoil, a well drained layer of gravel fill is topped with a layer of rigid foam, that the shallow footers are built on. Here's a well illustrated article that explains it.
        My geodesic oven project: part 1, part 2

        Comment


        • #5
          Re: How to construct Footers For Foundation

          For some reason I’m a little overwhelmed by the task - maybe it's pouring all of that concrete. I still haven’t heard from my concrete guy but I had an idea…

          What if I:

          Dig down 36 inches deep by 12 inches wide in a u shape
          Add +/- 6 inches of crushed stone at the bottom
          Put in a 6-8” deep footer of concrete and rebar
          Then build a 32” high cinder block wall (dry stack and then fill in the cores with rebar and concrete).
          I would then just continue the wall 32 more inches to the correct height I need instead of building a 32 inch wall under ground and then a pad on it. This way I would forgo the “actual” foundation pad at ground level. Inside the “U” I would just dig down a little and pour a free floating concrete pad for the “foundation” for the wood. Much like the one "solid foundation" poor posting but I would do mine with cinder blocks.

          I figure this way I could work at my own pace.

          Will this work/other suggestions.

          Thanks
          Dick

          Comment


          • #6
            Re: How to construct Footers For Foundation

            Almost perfect. If you dig three feet down, you pour your footers on bare earth, not rock fill. Pouring on crushed stone is for if you are doing the floating pad, or the shallow insulated footers.
            My geodesic oven project: part 1, part 2

            Comment


            • #7
              Re: How to construct Footers For Foundation

              Originally posted by thebadger View Post
              For some reason I’m a little overwhelmed by the task - maybe it's pouring all of that concrete. I still haven’t heard from my concrete guy but I had an idea…

              What if I:

              Dig down 36 inches deep by 12 inches wide in a u shape
              Add +/- 6 inches of crushed stone at the bottom
              Put in a 6-8” deep footer of concrete and rebar
              Then build a 32” high cinder block wall (dry stack and then fill in the cores with rebar and concrete).
              I would then just continue the wall 32 more inches to the correct height I need instead of building a 32 inch wall under ground and then a pad on it. This way I would forgo the “actual” foundation pad at ground level. Inside the “U” I would just dig down a little and pour a free floating concrete pad for the “foundation” for the wood. Much like the one "solid foundation" poor posting but I would do mine with cinder blocks.

              I figure this way I could work at my own pace.

              Will this work/other suggestions.

              Thanks
              Dick
              You just described the basic footing concept we used when I worked with my father back in PA on just about everything from apartment buildings to detached garages. Except for the gravel. But check with your building department they have a standard footing detail that is engineered for your area, it may include gravel or base-rock. You don't have to tell them all the details if your not going to pull a permit, just tell them you are in the planning stages.

              You are going to have to set the first course of block in mud to get it level though, the footing is always off a tiny bit. I would suggest laying the block this will save you the time and money of filling them which is not necessary and give you some time with the trowel that will benefit you later when it comes to the brick work. Also I would use 10" block till you get out of the ground then switch to 6".
              If you doubt that filling them is not necessary keep in mind standard basement foundations in the Tri-Stare area are not grouted and do not contain rebar. At least they didn't when I was working there that may have changed..
              Last edited by Unofornaio; 10-17-2007, 02:23 PM.
              http://www.palmisanoconcrete.com

              Comment


              • #8
                Re: How to construct Footers For Foundation

                Uno,

                Thanks.

                Just to clarify, I should just set the first course of block in the "mud" after I dig down. I thought it would be better to lay a concrete footer first (but I was wondering how I would level it at the bottom)... Do I'm going to have about a 6 foot "wall" ~3 feet below and ~3 feet above ground. Then my hearth will go on top - no real foundation pad.

                I will check but I think the gravel is a bad idea.

                So it sounds like this might work. I think this will be a little less intimidating to me as well.

                Is it okay to switch to 8 inch block? Also, if I have trouble finding 10 inch could I do the whole thing with 8 inch?

                Anything else I need to do? I was thinking about adding some rigid foam on the outside of the block walls below grade to help with insulation and water penetration - worthwhile?

                Thanks again - see the light at the end of the tunnel - at least for this part.
                Dick

                Comment


                • #9
                  Re: How to construct Footers For Foundation

                  Just to clarify, I should just set the first course of block in the "mud" after I dig down. I thought it would be better to lay a concrete footer first (but I was wondering how I would level it at the bottom)...
                  > I'm so sorry to throw you through a loop...In the biz we call mortar mud, actually we call concrete mud too, but in this case I was referring to mortar and this would be on the concrete footing.

                  So I'm going to have about a 6 foot "wall" ~3 feet below and ~3 feet above ground. Then my hearth will go on top - no real foundation pad.
                  > yes, thats right. Your concrete is the footing together with the blocks up to grade is your foundation, your concrete that will hold your wood (in between the block walls) is your slab on grade

                  I will check but I think the gravel is a bad idea.
                  > It may be in your area but its best to check

                  Is it okay to switch to 8 inch block?
                  >sure but 6 is fine and they will be a little easier to lay for you.

                  Also, if I have trouble finding 10 inch could I do the whole thing with 8 inch?
                  > you shouldn't have any trouble finding them. 8's I guess will be ok but I would be much more comfortable having the 10's below grade

                  Anything else I need to do? I was thinking about adding some rigid foam on the outside of the block walls below grade to help with insulation and water penetration - worthwhile?
                  >Not in my opinion. If you are worried about water just paint it with a foundation tar.
                  http://www.palmisanoconcrete.com

                  Comment


                  • #10
                    Re: How to construct Footers For Foundation

                    Uno (and everyone else)

                    THANKS!!!!

                    I feel good about this option - I know it's something I can handle and work on at my own pace to get it done.

                    Dick

                    Comment


                    • #11
                      Re: How to construct Footers For Foundation

                      Can't you just do a monolithic pour instead? You'll have your foundation and slab done all at once. Also, call a concrete company or ask a mason in your area what you should do as far as how deep, gravel, dimensions etc., etc. They're very helpful and doubt they will have a problem with giving you advice

                      Comment


                      • #12
                        Re: How to construct Footers For Foundation

                        Uno,


                        "You are going to have to set the first course of block in mud to get it level though, the footing is always off a tiny bit. I would suggest laying the block this will save you the time and money of filling them which is not necessary and give you some time with the trowel that will benefit you later when it comes to the brick work."


                        You are saying that you would morter between each brick instead of dry stacking, rebar and pouring concrete in the holes?

                        Would you tar the outside of the foudation? Where do you get hot tar?

                        fb66

                        Comment

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