Shop foundation questions

[73kay]

Hey all,

You guys have been great giving advise for my 30x40 shop I'm planning out. Now I got a few more questions. I'm planning on a 30x40x12 2x6 framed shop. I I live out in the county and have reached out to the county and wasn't given any specifics on what I'm building. The guy helping build the shop suggests our footer 1'x1' should be strong enough and the slab will be poured at the same time which as of now is 4in with an x brace that I assume goes from the corners of the footing. I do want to plan to add a lift later as money allows. Does any of this not make sense? There is a bit of a slope so we are gonna have to bring in full to bring the shop above the flow of water and bring the low side up. So far that is about 70 yards I am tracking. After the fill is spread/compacted the footer would be dug or framed out. I appreciate your feedback on all of this.

 

[850xpeps]

My preferred method would be a monolithic pour. Basically a thickened edge slab is what we call it up north. Edge would be 16”x16” and the underside would taper up at a 45 to the able thickness.


Quick and easy and strong as long as compaction of fill is proper. I would suggest clean rock as it doesn’t compact. Just needs a packer run over to kinda fix rocks. Also drains water. Go 5 or 6” thick slab. 10m rebar min 16” o/c and you get stirrups made for the thickened edge. Say you went 16” 16” then the stirrup would be 12” by 12” and tie into slab steel.


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[TTTTTT]

Here, a slab for a garage can be no bigger than 500 sq'. After that typical, build with footings 4' down or to bedrock, block or form walls to grade to support the structure and then compacted stone with poured concrete inside. I have a 20x 24 with the slab method, and unless the base is well prepared, shifting and then cracking may occur.

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[GMCGarage]

Hey all,

You guys have been great giving advise for my 30x40 shop I'm planning out. Now I got a few more questions. I'm planning on a 30x40x12 2x6 framed shop. I I live out in the county and have reached out to the county and wasn't given any specifics on what I'm building. The guy helping build the shop suggests our footer 1'x1' should be strong enough and the slab will be poured at the same time which as of now is 4in with an x brace that I assume goes from the corners of the footing. I do want to plan to add a lift later as money allows. Does any of this not make sense? There is a bit of a slope so we are gonna have to bring in full to bring the shop above the flow of water and bring the low side up. So far that is about 70 yards I am tracking. After the fill is spread/compacted the footer would be dug or framed out. I appreciate your feedback on all of this.

What do you mean X brace? In the slab? Something strange about that statement.

 

[850xpeps]

Here, a slab for a garage can be no bigger than 500 sq'. After that typical, build with footings 4' down or to bedrock, block or form walls to grade to support the structure and then compacted stone with poured concrete inside. I have a 20x 24 with the slab method, and unless the base is well prepared, shifting and then cracking may occur.

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Must have bad soil conditions as here we’ve done large commercial buildings in thickened edge slab way. Basically slab on grade or structural slab is the 2 ways we build. I would not build a slab with a footing and walls and have the slab sit on the walls unless it can support its own weight plus that of whatever will be on top. And keep it seperate from the ground because that will cause fracking unless you float the slab inside the walls.

 

[TTTTTT]

Must have bad soil conditions as here we’ve done large commercial buildings in thickened edge slab way. Basically slab on grade or structural slab is the 2 ways we build. I would not build a slab with a footing and walls and have the slab sit on the walls unless it can support its own weight plus that of whatever will be on top. And keep it seperate from the ground because that will cause fracking unless you float the slab inside the walls.

Sorry if not worded properly, the slab does not sit on the walls, its poured inside the foundation walls on a compacted base. The structure is supported by the footings and walls.

 

[850xpeps]

Sorry if not worded properly, the slab does not sit on the walls, its poured inside the foundation walls on a compacted base. The structure is supported by the footings and walls.

Ahhh ok ya that makes sense. Do you install like a knife board or something between slab and walls to let it move?

 

[My Old Tools]

If you are bringing in fill, any footings need to be deep enough to go into undisturbed earth.

 

[850xpeps]

If you are bringing in fill, any footings need to be deep enough to go into undisturbed earth.

Undisturbed earth can be 8” down where topsoil ends and clay begins. If a footing is to be used it needs to go down below frost line. Not to undisturbed soil. It needs to either rest on undisturbed soil or compacted fill.

 

[lakeroadster]

Undisturbed earth can be 8” down where topsoil ends and clay begins. If a footing is to be used it needs to go down below frost line. Not to undisturbed soil. It needs to either rest on undisturbed soil or compacted fill.

OP is from Kempner, TX.... frost line

If on compacted fill it should be tested. Undisturbed is a better approach since compaction testing on a residential project seems to be thought of as overkill and unnecessary by most GC's.

 

[850xpeps]

OP is from Kempner, TX.... frost line

Lol didn’t dig that deep into it..... but heard it was below freezing there a week or so ago.

I don’t think I would use dig down to undisturbed soil as the definition though. No point in a footing if only excavating 8” unless good soil is deeper. But undisturbed soil would not be the term I would use.

 

[My Old Tools]

Undisturbed soil is a hell of a lot better than bringing in 2 feet of fill and then digging a 12" footing in the fill.

 

[850xpeps]

Undisturbed soil is a hell of a lot better than bringing in 2 feet of fill and then digging a 12" footing in the fill.

The point is what is undisturbed soil to you? Lol 3” down? That’s undisturbed. Black dirt is undisturbed at 12” down if you don’t touch it. I wouldn’t put a footing on it.

 

[73kay]

Hey guys, sorry about the delay, here are some pics of the site.


The high ground is sloped up east. The low ground is west and the entrance is south. We got the batter boards up today to see how we look. We went a foot higher on the high side (according to the north east corner) which translated to about 22in from the low west side.

 

[mineallmine]

Here, a slab for a garage can be no bigger than 500 sq'. After that typical, build with footings 4' down or to bedrock, block or form walls to grade to support the structure and then compacted stone with poured concrete inside. I have a 20x 24 with the slab method, and unless the base is well prepared, shifting and then cracking may occur.

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Actually, that is slightly incorrect (unless your municipality has different rules).

I just built a 24x32 shop and while I did opt for the 4' full foundation walls with footings, you can do an engineered slab with thicker outer edges with rebar or mesh (whatever is required for design) and thinner in middle. A buddy of mine at work just built a 32x40 this way (can't remember exactly what they used but he definitely does not have a 4' foundation). I was given the option of the slab but wanted a raised curb wall so the foundation method became more practical.

To the OP; I would go thicker than 4" if you are considering putting in a hoist later on. 4" is minimum for a 10,000lb lift. It's always better to err on side of caution and go a little thicker. If you plan on a larger hoist 6" is minimum, so I personally would make sure the slab is at least 6" thick at least in the location you plan to place the hoist. That way you are completely sure you have a solid mounting location to handle it

 

[73kay]

Ya I've started planning where exactly I would put a lift and make that part of the pad thicker. Thanks mineallmine!