garage footings and stem walls

Discussion in 'Building Construction' started by ksharrison@gmail.com, Jul 6, 2006.

  1. Guest

    i am about to begin construction of a new garage. my plans call out
    for footing/stem wall construction. i have never done any foundation
    work before, but i'd like to do the forming/steel work myself and have
    a few questions.

    1. are separate pours required/recommended for the footings and stem
    walls, or can they be done at the same time?

    2. is it recommended to compact the footing trench and also put gravel
    under the footings?

    3. for a 6" high footing, is simply using 2 x 6 boards somehow staked
    into place acceptable?

    4. for the stem walls, do you cut the plywood to the height of your
    stemwall and control the height by slaking off excess as the forms
    fill? also, how do you secure the forms to the footing to keep them in
    place and plumb?

    any other advice for a first timer would be welcome. if there is a
    book or website out there that explains all this, please refer me to
    it!

    thanks!
     
    , Jul 6, 2006
    #1
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  2. James Guest

    While we are on the subject, can someone tell me what a stem wall is?


    Is that just another footing placed in the middle areas of the total
    perimeter, to give me support to the slab, or to major interior walls ?

    Thanks !!

    --James--
     
    James, Jul 6, 2006
    #2
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  3. marson Guest


    >
    > 1. are separate pours required/recommended for the footings and stem
    > walls, or can they be done at the same time?

    it might be possible to pour footings and walls in one fell swoop, but
    most everyone would use two pours. pour the footings, then you have a
    good base for your stemwalls.
    >
    > 2. is it recommended to compact the footing trench and also put gravel
    > under the footings?


    where i'm from, footings sit on undisturbed native soil.
    >
    > 3. for a 6" high footing, is simply using 2 x 6 boards somehow staked
    > into place acceptable?


    yes, 2x6's are fine for a 6" footing. you could even use a 2x4 and dig
    out 2 1/2 inches. stake them with wood stakes or buy steel stakes
    depending on your soil type. use a spreader across the top if you feel
    you need the extra strength.
    >
    > 4. for the stem walls, do you cut the plywood to the height of your
    > stemwall and control the height by slaking off excess as the forms
    > fill? also, how do you secure the forms to the footing to keep them in
    > place and plumb?


    yes, cut the plywood to the height of your stemwall. you should snap a
    line and nail a 2x ledger to the footing on each side of your wall.

    wall forms can be braced with 2x kickers down to the ground held in
    place by double 2x stakes.

    you don't mention how you will support the plywood. will you use snap
    ties and walers? there are a number of ways to do this, but you need
    to be prepared for a great deal of pressure on the forms from the wet
    concrete. a blowout is big, big trouble. also, you need a plan for
    placing rebar. usually vertical dowels are required. these can be
    drilled in after the footings are poured in some areas, though other
    jurisdictions will require you to have the verticals in place before
    the footings are poured. horizontals can be tied in when you are
    forming the stemwalls.
    >
    > any other advice for a first timer would be welcome. if there is a
    > book or website out there that explains all this, please refer me to
    > it!


    fine homebuilding put out a book on foundations that is pretty good.
    >
    > thanks!
     
    marson, Jul 6, 2006
    #3
  4. HerHusband Guest

    > i am about to begin construction of a new garage. my plans call out
    > for footing/stem wall construction. i have never done any foundation
    > work before, but i'd like to do the forming/steel work myself


    We poured our own garage foundation a few years ago. I had no experience
    in this area, and only did it myself because we couldn't find a
    contractor who would take the job. It took a couple of months of work,
    but it was really satisfying to do it ourselves, and the foundation
    turned out great.

    > 1. are separate pours required/recommended for the footings and stem
    > walls, or can they be done at the same time?


    There was an article in Fine Homebuilding a while back about doing a
    single pour, but I think most people would prefer doing separate pours. I
    personally poured the footings first, then did the walls. Much easier for
    an amateur.

    > 2. is it recommended to compact the footing trench and also put gravel
    > under the footings?


    Usually you'll want to dig down to undisturbed soil and pour directly on
    the ground. If you have to pour your foundation on fill for some reason,
    you'll probably need to check with your building department for what is
    required in your area. They may require pilings or special compaction
    before setting the forms.

    > 3. for a 6" high footing, is simply using 2 x 6 boards somehow staked
    > into place acceptable?


    Yes, you can just dig out an extra 1/2" inside the footing forms.

    However, unless your site is already fairly level, you may need a variety
    of form sizes. I ended up using a combination of 2x6's, 2x8's, and a
    couple of 2x10's to accomodate dips in the excavated site. Mostly due to
    sloppy excavation work. Pile dirt against the outside of the forms to
    keep concrete from oozing out under the forms.

    I used 2x2 wood spreaders to tie the inner and outer forms together at
    the correct distance.

    > 4. for the stem walls, do you cut the plywood to the height of your
    > stemwall and control the height by slaking off excess as the forms
    > fill?


    We wanted 2' high stem walls, so I built 2'x8' wall forms out of 3/4"
    plywood and a 2x4@24" OC framework. I leveled the forms on the footings,
    then screeded the concrete along the top of the forms.

    We reused the forms to pour our house foundation, then I sold them to a
    farmer who used them to build structures for his animals.

    > how do you secure the forms to the footing to keep them in
    > place and plumb?


    I left my footing forms in place while I poured the walls, and just
    screwed the wall forms to the tops of the footing forms. The footing
    forms were already staked and braced with dirt on the outside. I did add
    a few concrete nails into the footings to add a little extra support.

    As for the tops of the forms, I installed 2x2 spreaders to keep the forms
    tied together at the right distance. Then I installed diagonal braces
    every 8' on the inside and outside of the forms. These attached to stakes
    driven in the ground to keep the forms from tilting or shifting as the
    concrete was poured.

    I wanted a little extra insurance, so I bolted the inner and outer forms
    together every 8' or so. I installed a short piece of PVC pipe as a
    spreader, then passed the bolt through that, with big washers on each
    side of the form. The pipe let the bolt come out easily, and the PVC is
    easy to tap out and patch the hole with grout after the pour. They make
    special form ties for this kind of thing, but the bolt approach worked
    fine for me.

    > if there is a book or website out there that explains all this


    My favorite books are no longer in print, but your local library should
    have plenty of books showing how to do concrete work. You could also
    check out Fine Homebuilding magazine, and the books offered by Taunton
    press.

    When you get to the framing stage, one of my favorite books is "graphic
    guide to frame construction". It's more of a reference manual than a how-
    to guide, but I liked it a lot.

    Also, different areas have different requirements (soil types, seismic
    risks, etc.), so check with your building department to see what is
    needed in your area. They'll have requirements for footing sizes, the
    size and locations of rebar, etc. We had to install special tie downs in
    the foundation walls on each side of the garage doors to keep the
    building on the foundation in case of an earthquake.

    When you are pouring your concrete, take a long stick and "jab" up and
    down along the inside and outside of the forms. This will work out air
    bubbles that may form as the concrete is being poured, so you don't end
    up with voids when the forms are stripped. This is especially important
    around doorway openings, foundation vents, etc.

    The pour itself goes FAST, usually less than an hour per pour. But,
    you'll work harder in that half hour than you did all week! :) According
    to code, you should also leave the forms on a full week before stripping
    the forms. And, cover the concrete with plastic to protect from rain and
    keep evaporation to a minimum.

    We used a company with trucks that mix the concrete on-site. If these are
    available in your area, I highly recommend them. You only pay for the
    concrete you need, you don't have waste to dispose of, and they can
    usually provide a little extra if your calculations were off a bit.

    Basically, just do your research, take your time, and do a good job. The
    rest of the building depends on the foundation, so you don't want to cut
    corners here.

    Compared to the rest of the building, the foundation takes a lot of time
    and work. You spend a lot of time building the forms, only to tear them
    down again after the pour. It's a great feeling when you finally get "out
    of the dirt" and start framing!

    Anthony
     
    HerHusband, Jul 6, 2006
    #4
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