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Thread: Off topic- calculating concrete yardage for new shop build.

  1. #1

    Off topic- calculating concrete yardage for new shop build.

    So I am looking at building a new 60ft x 120ft shop building on some property that I have owned for a while. I got a quote on a kit from one of the largest metal suppliers in the US. The kit comes with everything needed for the metal framing, the metal for the walls, the metal for the roof including all necessary roof accessories such as closures and such as well as the entry door and garage door. All of the metal is pre cut and has the mounting holes already drilled. All that I have to do is supply the pad with the anchor bolts and do the assembly. The quote they gave me for the building with everything needed for a turn key job including rolls of insulation for the walls and ceiling for a 60ft x 120ft kit was a little over $46,000. I just supply the pad and do the assembly myself.

    My question for you guys is how to calculate the concrete yardage for a slab of this size? I live in Arkansas and we rarely get snow although I would like to possibly insulate the slab. Of course I would hire a concrete company to handle all of the slab work. I am just trying to come up with a quick and dirty approx calculation for the concrete. Would I be good with a slab thickness of approx 4 to 6 not including the footer? Not really sure on the PSI either but I will let the concrete guy figure that stuff when I decide to start. For now I am just trying to come up with a rough guesstimate for rough budgeting purposes.

    Can anyone give me an idea of how to calculate rough yardage?

  2. #2
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    (60'x120'x.33')/27 =89 cy at 4" thick, 133 cy at 6" thick. 4" is fine unless you will be running heavy equipment over it. Personally I like to have them add fiber to the mix, it is a cheap way to further reinforce the slab. Check local code for footer requirements, it will add to your concrete volume.
    NOW you tell me...

  3. #3
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    That last thing that Ole mentions is pretty important for two reasons. Firstly, it's always important to know what the local rules are and follow them, even where they might be "light" due to rural location, etc. Secondly, and actually more importantly, the edge of the pad where the building actually connects has got to be able to support the weight and stress load of the building structure that's fastened to it. That's where the footer requirement comes in...it's not just about weather, but also what load it has to bear. This is an engineering matter and should be addressed by the same.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  4. #4
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    That's going to be a big building. I would suggest going 6" because you won't regret going heavier. Also if you set it up for heat in the floor and insulate underneath even if you don't heat it immediately you won't regret it. Make sure that the concrete is rebar reinforced and of course sawed appropriately so it hopefully cracks where it's sawed and not just anywhere. Two things about concrete is it will get hard and it will crack. A properly prepared base under it is critical as well. If you have questions on the floor heat there are a couple good resources for that.

  5. #5
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    Quote Originally Posted by Jim Becker View Post
    That last thing that Ole mentions is pretty important for two reasons. Firstly, it's always important to know what the local rules are and follow them, even where they might be "light" due to rural location, etc. Secondly, and actually more importantly, the edge of the pad where the building actually connects has got to be able to support the weight and stress load of the building structure that's fastened to it. That's where the footer requirement comes in...it's not just about weather, but also what load it has to bear. This is an engineering matter and should be addressed by the same.
    Actually for that size building a poured footing would be the way to go that's not dependent upon the slab to support the building. Even if you don't get much snow it is just the best way to go on this type building. However don't rule out post frame construction. (pole building) By the time you factor in the footing cost you may not be any higher. That and they will come in and erect it in a few days time. The concrete can be done at your convenience.

  6. #6
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    Highly recommend you have the building pad put in ASAP.
    The longer the pad has to settle the less cracking of the concrete floor.
    Strip the top soil, then build the pad up above the surrounding area at least a foot
    Then you can decide what kind of building, footers or piers, etc
    Sooner the better on a properly constructed pad. Let mother nature help with settling it down.

  7. #7
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    The company should supply foundation plans with bolt locations. They may have several styles with single slab or a thicker perimeter foundation.
    Bill D

  8. #8
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    You mention insulation, does that mean ground that will freeze? A slab of that size around here would need joints for expansion/ contraction. As the cement moves it'll crack in the expansion joints vs random cracks. I like to do anything I can myself but unless you are 100% certain you know what you are doing this might be something to hire out. With a building of that size I would want pads to support the steel columns or maybe an Alaskan slab with plenty of rebar in it.

  9. #9
    I built a 50 x 80 steel building a few years ago, my trusses were on 12' centers, and I put 18" diameter holes 4' deep for the piers, and marked on the forms where the anchor bolts go. Made a couple of plywood guides drilled for the holes that I could lay on the concrete and push the bolts into the concrete. I also poured a curb between the piers, just 12" x 12", to tie things together, and wrapped 2 rows of 1/2" rebar all the way around the perimeter. When I put up the building, all the bolts fit the steel.

  10. #10
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    And don't even think about trying to pour a slab that size DIY.
    NOW you tell me...

  11. #11
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    Quote Originally Posted by Ole Anderson View Post
    And don't even think about trying to pour a slab that size DIY.
    I always pay someone to pour and surface the concrete but I do the prep myself - compacting the soil, gravel, forms, footers, etc. Fiber is a good idea but I always add plenty of rebar. As a former concrete inspector, I've seen to much - I don't trust others to do it right. Some don't even ensure the rebar is at the proper vertical position in the slab so I prep it so they can't mess it up. (For example, many use cheap plastic "chairs" to hold the rebar in the right position but what no one but the guys pouring the concrete know is many of these collapse when they step on the rebar and push the rebar to the ground where is not effective. Better to use strong steel chairs or properly sized pieces of broken cinder block or brick. Some installers just lay the rebar on the ground and pull it up into place at some point during the pour - if they remember...)

    Rebar also goes in the footers or turn-downs and is tied to the slab rebar. I installed rebar on 24" centers for my 4" slab in the main shop and at 12" centers for the 6" concrete in the back part of the shop so I can bring in tractor, etc. as needed.

    shop_rebar_IMG_20130918_164455_2.jpg

    Real expansion joints are a good idea for that huge slab, even in your mild climate. Most surfacers cut grooves at 10' or 12' centers after the concrete is cured to direct the cracks that will certainly happen. The rebar will hold the pieces together after the slab cracks in the grooves.

    Another thing some concrete contractors skip is properly curing the concrete. I cover mine with poly and keep it wet underneath for at least a week.

    JKJ

  12. #12
    Quote Originally Posted by Dan Coker View Post
    So I am looking at building a new 60ft x 120ft shop building on some property that I have owned for a while. I got a quote on a kit from one of the largest metal suppliers in the US. The kit comes with everything needed for the metal framing, the metal for the walls, the metal for the roof including all necessary roof accessories such as closures and such as well as the entry door and garage door. All of the metal is pre cut and has the mounting holes already drilled. All that I have to do is supply the pad with the anchor bolts and do the assembly. The quote they gave me for the building with everything needed for a turn key job including rolls of insulation for the walls and ceiling for a 60ft x 120ft kit was a little over $46,000. I just supply the pad and do the assembly myself.

    My question for you guys is how to calculate the concrete yardage for a slab of this size? I live in Arkansas and we rarely get snow although I would like to possibly insulate the slab. Of course I would hire a concrete company to handle all of the slab work. I am just trying to come up with a quick and dirty approx calculation for the concrete. Would I be good with a slab thickness of approx 4 to 6 not including the footer? Not really sure on the PSI either but I will let the concrete guy figure that stuff when I decide to start. For now I am just trying to come up with a rough guesstimate for rough budgeting purposes.

    Can anyone give me an idea of how to calculate rough yardage?
    A yard of cement is literally a block of concrete 3'x3'x3'. At 4" thick you could get 9- 3'x3' sections of floor or 81 square feet. At 6" you could get 54 square feet. Unless your soil is very soft or plan to drive heavy equipment on it 6" is a waste. I built a bridge on my place with a 6" slab and have had cement trucks with 10 yards of cement drive over it.

  13. #13
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    Calculate concrete volume in yards. All dimensions in "feet''. Thickness x width x length divided by 27.

  14. #14
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    I built a salt storage building that had 4 inch concrete and the trucks loaded with 10 tons haven't ruined it.

  15. #15
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    Around here, no one presets anchor bolts, any more. Now, they're all drilled in place after the slab is finished. Sure seems like a lot less trouble. If it's going to be slick finished, I wouldn't want fiber in it.

    edited to add: If you're going to install a two-post auto/truck lift, check with the lift manufacturer. Some call for 8" where the lift will be anchored to the floor. The whole floor doesn't have to be that thick, just an area where the lift posts will go.
    Last edited by Tom M King; 11-18-2019 at 4:23 PM.

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