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  1. #1
    Bob F. Guest

    Default Adding brick ledges to existing foundation

    I'm looking for ideas on how to solve a problem I face with a recently completed ICF foundation, and plans for the addition of a concrete floor slab. The foundation wall rests on footings that are stepped in places to accommodate frost wall depths. However, as the walls were erected and subsequently poured, I realized that a brick ledge, level with the top of the footing, had not been provided in short sections of the wall where the frost wall (which will exist below the level of the slab, roughly four feet) and the basement foundation wall (extending up to the sill plate above the level of the slab) are all one straight pour.

    I realize the floor slab should have its edges resting on the remaining footing space still extruding in from under the base of the basement foundation. But, shouldn't it also have some support where it just butts up against the frost/foundation wall as well? My way of thinking (in hindsight, unfortunately) is yes, it should. Some system of brick ledge could be added to provide this support, even if just in some very short spans.

    My question is actually, given my resolve to do this, how would I go about tying in a brick ledge to the existing pour? I'm assuming I'll create some kind of wedge-shaped form, maybe each form roughly 12" long, have it temporarily held or pinned in place, and then pour in the concrete, so the top of the wedge of concrete forms a shelf, even with the level of the existing footings. How can I ensure the "wedge" of concrete and the existing wall bond together? I know I'll have to remove the existing ICF form at the point of contact - a rectangular section as large as one side of the wedge. Should I drill into the existing concrete wall then, and epoxy some sections of rebar to pour around? I was thinking, perhaps a "laddder rung-like" protrusion, calling for two holes per wedge, and then center this into the upper part of the wedge to surround it with as much concrete as possible. Would this work?

    Any thoughts you folks may have, are greatly appreciated. Don't hesitate to let me know if I'm way off base here as well.

    Thanks!

    -Bob

  2. #2
    Brad Guest

    Default Re: Adding brick ledges to existing foundation

    Bob
    If I am visualizing your problem correctly it sounds as if some of the perimeter of your SOG would not be resting on some footing or top of wall but on uncompacted interior backfill. You can simply support the edge with rebar dowels drilled and ideally epoxied into the wall, but since I am not familiar with the ICF system I could be off base here.

  3. #3
    Bob F. Guest

    Default Re: Adding brick ledges to existing foundation

    Brad,

    I think you've got a good idea of my dilemma. Probably 75 to 80 percent of the SOG would be supported by the existing footings; the rest would just butt up against the ICF panels, over an area where the interior backfill is previously excavated material, possibly compacted, along with gravel and possibly a styrofoam insulation board extending under the SOG.

    I was thinking support would need to come from underneath, but I believe your idea has merit. Given an 8" foundation wall into which the dowels would be epoxied, and a 4" SOG, what might be the spacing requirements along the perimeter, and depths into which the dowels would need to penetrate both the wall and the slab? Would you have the dowels positioned right in the middle of the slab thickness, at 2" from the surface top? I realize other intangibles are necessary to get the entire picture - I'm just looking for some general guidelines.

    Thanks again for your help!

    -Bob

  4. #4
    Rollie Peschon Guest

    Default Re: Adding brick ledges to existing foundation

    It may sound odd, but if the ICF is made of 2LB density foam, You could very well get by with taking the foam out from the top of the slab, down 6 inches or so, and support the slab edge by the 2lB density foam. The compressive strength of the foam is actually considerably higher than most people give it credit for. It does hold the concrete in the wall during the pour, dont it. I would do this in conjuntion with the rebars, but would not install the rebars in the middle of the slab, but would drop them to the bottom 1 1/2 inch of the pour. say 4 1/2 inches below TOS.

    Another route would be to install angle iron from the footing up to the bottom of the slab say every 4 ft, and then take a 4 inch angle iron, and set it on top of the vertical legs to span between the legs. Let the fill hold it in place till the pour is installed.

  5. #5
    Rollie Peschon Guest

    Default Re: Adding brick ledges to existing foundation

    Either of these approaches would be way less money than trying to hang a brickledge , which could very not work as well as either of the options. Just my $.02

  6. #6
    Danny Waite Guest

    Default Re: Adding brick ledges to existing foundation

    How about just excavating out a deep thickened edge for your slab so it pours monolithically all the way down to the lower existing footing edge. Lay in a little bit of rebar to tie it all together. Maybe no need to dowel into the existing ICF wall. Maybe I don't fully understand what it is exactly the problem is.

  7. #7
    Bob F. Guest

    Default Re: Adding brick ledges to existing foundation

    Rollie,

    Thanks for the post - I see your point. The ICF foam density is 2LB, I believe, and would only take about 20 feet or so along the perimeter of removing the foam to provide the additional "ledge" of foam board edge to support the slab pour! Good idea, and along with the rebar, a permanent connection to the wall would be made. I follow your point to provide more of the thickness of the slab ABOVE the rebar - makes sense to maximize the rebar's strength as close to the bottom of the slab as possible.

    One other question - how far apart might you space the rebar dowels? I know it's hard to picture the whole scenario - I'm just looking for a ballpark figure.

    Thanks again!

    -Bob

  8. #8
    Bob F. Guest

    Default Re: Adding brick ledges to existing foundation

    Danny,

    I know this problem is difficult to picture - I had actually considered your idea originally as well. The area is already excavated, but falls off to roughly four feet below what would be the bottom of the slab. I've seen diagrams where the slab thickness at the edge is depicted as be much thicker then the overall thickness of the slab, say, "in the field", but I thought four feet thicker might be a bit much.

    And true, the extra concrete probably wouldn't cost a whole lot more than labor to dowel in the rebar hangers. Well, it's still an idea worth considering!

    Thanks for your help!

    -Bob

  9. #9
    Brad Guest

    Default Re: Adding brick ledges to existing foundation

    Bob
    Sounds like if you can remove the foam and actually get some bearing out of the foam, the rebar would really tie things together. I hate to make engineering recommendations that could be wrong but if it were my slab and there was no additional bearing other than floor load, I would use #4 bars at 12" oc. With a roto-hammer and a 1/2" bit the dowells can be installed generously and quickly. You can rent one if you do not own one. I would install in the middle of the slab to give a little fudge factor since you will probably not install the dowell dead level.

  10. #10
    James Eggert Guest

    Default Re: Adding brick ledges to existing foundation

    Bob
    I build with ICF's and had a hard time figuring your post out at first, at least until everyone else put it in perspective. If I have it right, you must be building on a pretty steep sloped site? This much variation is rare, but maybe I'm still not seeing the picture. Anyway, even though something was missed in the setup for this pour Brad has a pretty good idea for the dowels, and I would use an 8" perimeter haunch for a 4" slab. Adding a #4 perimeter bar tied to the dowels about 6" away from the wall, the concrete part because you can remove the foam easily with any brand ICF, should tie every thing together pretty well.
    If you can't compact the backfill? you may try using a peagravel backfill which pretty much self compacts.
    Are you using ICF's for all floors? We're under way with one right now and the top of the second floor is 28' off the footing.

    Jim

  11. #11
    Rollie Guest

    Default Re: Adding brick ledges to existing foundation

    I would install the rebars 24 inches on center. Use 5/8, and extend them out to where there is firm ground to support the slab. I would still keep them in the bottom third of the concrete because the loading is downward, and if there is some movement in the slab downward any where nearer the surface may end up fracturing the surface out.

    One other thing you could do is dry-stack some 4X8X16 inch block, backfilling against them as you go, and bringing them up to a level just below BOS. That would be fairly simple fix, and wouldnt require all the drilling time. Of course, since you are adding approx 4 ft of fill, you should still reinforce with steel to hold it together incase it decides to go south inside of the line where it is supported by the brickledge or how ever else you decide to support it. Enough options to give you something to think about anyway. my $.02.

  12. #12
    Bob F. Guest

    Default Re: Adding brick ledges to existing foundation

    James,

    Thanks for your thoughts.

    I know the explanations I've provided probably don't due the situation justice, so I'll retry:

    Picture a basic box to represent the basement foundation walls. This entire box is below grade, and is supported by a spread footing which in turn provides a roughly 4" ledge around the interior perimeter of the box to support a SOG.

    Here's the problem. On one side of this box, near a corner, a 6' patio walkout is provided for at this basement level. The architect called for frost walls underneath this door, as well as for about six feet on either side of this opening. On one side of the opening, this frost wall actually follows the 90 degree bend in one of the corners. The footing contractor solved this issue with step footings, as would be expected. The majority of the box rests on upper footings, while a section of one of the walls, and a liitle bit of a section around the corner of an adjacent wall rest on a footing poured 4' below the upper footing.

    The ICF contractor simply built up the entire box sides to same level above grade (16" blocks, 7 courses above the level of the slab). However, where the step footings are placed, 4' below where the slab would intersect the wall (and the opening for the patio walkout), the ICF stack begins 3 course below the ICF stack for the rest of the box, and goes up to the top 10 course high. One straight, up and down smooth wall - no ledge, no protrusions.

    The frost wall was called for because the rest of the box is all underground - the majority of the footings are below frost level. The six feet of exterior ground on either side of the patio walkout will be graded and retained to keep all footings below the frost level.

    I hope this helps paint a better picture. This explanation, by the way, is a bit simplified as well. Some of the walls have angles, as well as a basement slab actually acting as a garage floor slab as well, with a garage door entrance and entry door similarly provided.

    Thanks again for all your suggestions!

    -Bob

  13. #13
    Rollie Peschon Guest

    Default Re: Adding brick ledges to existing foundation

    Sounds to me like the architect should learn about Shallow Frost Protected Foundations. Wouldve saved everyone involved a considerable amount of time, material and money. My $.02

  14. #14
    Danny Waite Guest

    Default Re: Adding brick ledges to existing foundation

    Typical architect that maybe doesn't know what he doesn't know but sure knows how to charge for it.

  15. #15
    Rollie Peschon Guest

    Default Re: Adding brick ledges to existing foundation

    It was not my intent to strap all the blame onto the architect in this case. All involved could learn from SFPF technology. My point was that SFPF more than likely wouldve been a considerable savings of money on this particular project

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