Concrete foundation for shed

[UpToNoGood]

I want to do some foundation work myself and have never worked with concrete other than mixing a bag and dumping it in a hole for a fence post.
Any way I picked up 40 acres and want to build a vacation/retirement house over time, but figured I would start with a shed first.
I want the shed to have a concrete floor and maybe cinder blocks for 2 layers followed by wood and a Metal roof.
I am not going to work the concrete when it is poured that would be hired out for sure.
I do plan to set the form myself before the concrete is poured. About 15x20. So my question is would re-bar be needed or could I just use the wire mesh?
I will also be setting a form for a 500gal propane tank to sit on for the same concrete pour.
Think 5 inch thick will be fine for both?

 

[mchildress]

I would use rebar and might think about a perimeter beam around the outside edge.

 

[UpToNoGood]

What is "a perimeter beam"?

 

[mjncad]

If you're going to form it yourself; then I assume you'll be doing the reinforcement yourself.

In any case, I'd go with rebar on chairs regardless of who installs the reinforcement. WWF (Welded Wire Fabric) is always thrown on the ground and the concrete contractor says his guys will pull it up to the middle during the pour. Yeah right as the guys doing the pulling are also walking on it. Besides, do you want to wrestle with a roll of fabric that doesn't want to lay flat without persuasion?

5" thick should be adequate, 6" is better. Just make sure you have 2-1/2" and preferably 3" of concrete cover over your reinforcement. #4 (1/2") rebar 24" O.C. each way should give you a pretty strong slab. Put a control joint in each direction and you should be good to go. Sawcut control joints are better than tooled joints, especially if you're going to have anything on casters in the shed. A 3/4" - 1" deep sawcut is adequate. You can even rent a walk behind concrete saw and do the joints yourself. You can always caulk the joints to keep crud out of them.

 

[crash325]

Just my way of thinking.

It would be best if you got someone that has done concrete work to help you. Reading about how and what is not the same as having done it.

Yes you should use Re-bar, but is a waste if not done correctly.

 

[mjncad]

What is "a perimeter beam"?

Also known as a grade beam if separate from the slab or a thickened edge if part of the slab. A thickened edge will beef up the slab. Say 2 - 3 times the slab thickness, about 8" - 12" wide with a 45-degree transition from edge bottom to the slab bottom.

What's you frost line?

 

[UpToNoGood]

I am fine with using Rebar.

The frost line is about 2 feet.

 

[TedLaRue]

Sorry for this long post. I got carried away.

I also recommend rebar on chairs instead of mesh. The savings from using mesh would be insignificant compared to the peace of mind from using rebar on your small slab.

You can buy plastic chairs to hold the rebar up to about 1/2 the thickness of your slab, or you can use rocks/stones/bricks that are about the right thickness. Don't use wood; it will wick moisture up to the rebar and cause it to rust.

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Around here, 4" is a standard slab thickness, and should be sufficient for a shed floor. While typing this, I see others have recommended 5" or 6", but I think that is overkill for a reinforced shed floor. I also think control joints are unnecessary for an indoor floor unless you expect the underlying soil to be very moist and also subject to serious freezing.

Also, around here under the slab we lay down some sand or gravel covered by a layer of builder's plastic to control moisture. That may be overkill for a shed, especially in your area.

You didn't say anything about a footer (others are calling this a "perimeter beam") around the perimeter, and since I'm not familiar with Texas soil structures, I'll leave that to someone else. If you don't need a full size footer, you might consider digging a trench around the perimeter a little deeper than your slab to give you some extra thickness there.

A full size footer/perimeter beam should be twice as wide as it is thick, and twice as wide as the blocks you are using as your foundation wall. For example, if you are using 8" wide blocks, then the footer should be 16" wide, and 8" thick. If you have special soil conditions, then those numbers might be different for you. There should also be two bars of rebar running down the center of the footer's thickness and spaced about 9 to 12 inches apart with pieces wired together where they overlap.

That is probably overkill for your short 16" tall block wall, but you should probably have a little more thickness around the perimeter, and make sure there is at least one stick of rebar in it.

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For our propane tank, I poured two separate mini-slabs, one for each "leg" of the propane tank. I chose two thick mini-slabs rather than one long thinner slab. Less chance of a crack developing in the middle. Just make sure the distance between the centers of the slabs matches the distance between the legs on the tank. Your propane supplier can tell you the distance between the legs.

 

[TedLaRue]

Something else to consider:

In some locations you will be taxed for "permanent" buildings, but not for temporary buildings. If you build a shed having 4x6 timbers serving as "skids" as the foundation, you can move it, so it isn't permanent and not taxable. If you pour a slab, it is permanent and taxable.

 

[UpToNoGood]

By the way this is going in New Mexico. It is considered high desert at 7400ft.

 

[TedLaRue]

By the way this is going in New Mexico. It is considered high desert at 7400ft.

Ohhhhh! Then definitely consider a reinforced footer/perimeter beam below the frost line.

By the way, 15 x 20 seems an odd size considering that most dimensions in the USA are multiples of 16" (e.g. 4'x8' plywood sheathing, and also 8"x16" concrete blocks). Perhaps 16' x 20' as dimensions for the outside edges of your framing would be a better choice? or even 16' x 24' so you can run a 30" wide workbench 8' down the long side, and put 12" wide shelves floor to ceiling along the rest of it. Drool drool.....

 

[UpToNoGood]

15x20 or 16x20 doesn't matter to me. I need to measure the bricks and work from there. I will be dry stacking them so I need to figure what would fit with the least cutting. I want the two rows of bricks to keep the wood off the ground. So if I go 16x20 the shed will only be 16x16 and the extra concrete will be a porch with roof over top. I want to use that area to hoist up Elk for skinning and it will keep them out of the sun/weather as well. I have a reason for everything and it will all work out in the end.

BTW just to prove my point I work on computers for a living and I built a pergola for my house and never had any of the plans on paper. My wife went nuts wanting to know if it was going to work or not. I had never did anything like that before and I think it turned out well. Look for your self.

 

[TedLaRue]

UpToNoGood, I could tell from your original post that you were the kind of guy to think things through and plan ahead!

Sometimes our replies are aimed at the general public who might be reading this thread a year from now, so please don't take it personally if we give an answer to a "dumb" question which is something you already know.

For what it's worth, I teach math and computer science at our local university, but I'm also up to no good (without pay!) during the summer, building things and tearing up things.

If you're planning to lay up the blocks dry, then be aware that a 16" block is actually 15-5/8" long to allow for a 3/8" mortar joint. Be sure to consider this in your plans or when you lay the blocks dry or mortared.

 

[UpToNoGood]

I am not taking any of this personal. I soak all this up like a sponge trying to learn as much as I can before doing anything. I am the "Measure twice cut once guy".

As for the blocks I have learned a lot here DryStacked Surface Bonded Home Construction Sequence with Dry Stacked Block Walls and only going two rows I don't think I can fubar that up.

Thanks for all the help so far.

 

[BoFuller]

15x20 or 16x20 doesn't matter to me. I need to measure the bricks and work from there. I will be dry stacking them so I need to figure what would fit with the least cutting. I want the two rows of bricks to keep the wood off the ground. So if I go 16x20 the shed will only be 16x16 and the extra concrete will be a porch with roof over top. I want to use that area to hoist up Elk for skinning and it will keep them out of the sun/weather as well. I have a reason for everything and it will all work out in the end.

BTW just to prove my point I work on computers for a living and I built a pergola for my house and never had any of the plans on paper. My wife went nuts wanting to know if it was going to work or not. I had never did anything like that before and I think it turned out well. Look for your self.

Nice work.

 

[BoFuller]

I am not taking any of this personal. I soak all this up like a sponge trying to learn as much as I can before doing anything. I am the "Measure twice cut once guy".

As for the blocks I have learned a lot here DryStacked Surface Bonded Home Construction Sequence with Dry Stacked Block Walls and only going two rows I don't think I can fubar that up.

Thanks for all the help so far.

"fubar" - I haven't heard that term for a long time. It's bringing a chuckle or two. Thanks for making my day. :thumbsup:

 

[KennyG]

One option you might want to check with the local concrete guys is fiberglas reinforcement. The fibers are mixed and poured with the concrete. It avoids the hassle of rebar placement and the movement that often comes with wire mesh. The fibers aren't as strong as steel which means you have to be careful using it for slabs exposed to the sun but for a floor in a building it works great.

I have a floating slab with fiberglas in Michigan that was poured 12 years ago and it doesn't have a single crack.

 

[Cat_Driver]

One option you might want to check with the local concrete guys is fiberglas reinforcement. The fibers are mixed and poured with the concrete. It avoids the hassle of rebar placement and the movement that often comes with wire mesh. The fibers aren't as strong as steel which means you have to be careful using it for slabs exposed to the sun but for a floor in a building it works great.

I have a floating slab with fiberglas in Michigan that was poured 12 years ago and it doesn't have a single crack.

x2 on the fiberglass reinforcement, or you can use stainless steel also. I laid a slab on beach sand with fiberglass reinforcement and drive 10K tractors on it and never a crack.

I think it cost me under $20.00 to add it to the load of concrete.

Definitely look up fiber reinforcement for concrete you will get a great education on how strong it makes concrete.

 

[Deere Dude]

Something I would consider would be to cement into the floor some threaded rod to go up through the blocks in order to bolt the wood to it. At least the wall wouldn't slide off the blocks in a slight wind. Also I would mortar between all the blocks to keep any little critters out and also fill a hole to the top in the concrete blocks with concrete, maybe every 4 feet. Doing those things will really sturdy the blocks up. Just my 2c :thumbsup:

 

[beeforty]

Nice Pergola:thumbsup: Make sure you have a 33' tape measure so that you can measure corner to corner for squareness. A 30' isn't long enough for your size. That and make sure your sides are level or else your walls start leaning and it only gets worse when you get to doing the roof. I built on a slab your size that was poured by some else and it was racked 11" out of square, talk about fudging to make it fit:confused2: