Advice needed on constructing a small perimeter foundation

kudzu9August 31, 2006

I'm going to erect a small greenhouse (10' X 15') on my property and am planning to set it on a perimeter foundation, and then lay bricks-in-sand for a floor. I'm pretty experienced with carpentry and remodeling, and have poured slabs before, but have never built forms for a stem wall. I'm trenching down 18" and pouring a 10" wide by 6" thick footing, and then I want to pour a 2' high and 4" thick wall on top. That would give me a perimeter wall that stands 12" above grade.

I have a cement mixer that can do about 3 bags at a time and will mix and pour myself. What is the most inexpensive material I can use for my forms (for example, can I use 1/2" sheathing)? How closely spaced do the metal ties need to be? Do I need to build the forms for all 4 walls at the same time, or can I maybe do two walls and then re-use the form materials for the remaining two? Given that the weight of the greenhouse is only 1200 pounds, what's the smallest rebar I can use?

I'd appreciate any input on how to do this easily and cheaply. If anyone knows of a good do-it-yourself book on this subject, please mention it. Thanks

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This is not my area of expertise, but I'm wondering where you live and how deep the frost line is. I'm in Ohio, where it's a lot deeper than 18".

Engineering aside, 50 linear feet of 10" x 6" footing is three quarters of a cubic yard, or something like 60 bags of concrete. Even with a short-load fee, it might be cheaper (besides being a whole lot quicker and easier) to get the concrete delivered ready-mixed.

    Bookmark   August 31, 2006 at 8:22AM
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The crew that formed and poured for an outbuilding on our property framed 2x4's 16" o.c. and skinned with 1/2"osb. The ties were placed 6"from the corners and where the forms butted, and every 16" in the field of the forms.They used 3/8" rebar. After the footings were poured, they formed the whole stemwall and poured the stemwall complete.If you can do this, it would probably be a better pour, as pouring sections might result in weak joints where the existing and new come together. Have you considered block foundation? Looks great,you can work it at your leisure, and will support the weight of your structure easily, although i would still fill each cavity with crete.Jon's advise of getting ready mixed is great advise as a stemwall would be hard to keep up with using a mixer ,especially if your flying solo!

    Bookmark   August 31, 2006 at 12:12PM
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Thanks for the input. I live in a temperate area and code only requires 18" depth. My location is a place where you can't get a concrete truck to, so the total charge for concrete, short load, and pumper is about $1000, which is why I want to try it myself. As for concrete block, that's an idea that I'll consider.

    Bookmark   August 31, 2006 at 12:52PM
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