Concrete slab cost

[gregfender]

I am looking to put down a 20x30 concrete slab for a shop/shed I am going to build. Thickness will be 4". Have any of you folks had concrete work done recently and know a good ballpark estimate for a simple slab?

 

[CurlyDave]

In my neck of the woods concrete is about $120/yard. Your dimensions calculate to just under 8 yards, but if you need a footer around the perimeter, or even just a thicker slab, you should count on 9 to 10 yards. I would use 1/2" rebar on 2' centers in both directions, plus some extra in the perimeter, I would say 45 sticks of rebar at about $8-9.

If you do the prep work yourself, you will need about 8-9 yards of gravel or sand to go under the concrete at maybe $20/yard. You need to rent a compactor to compact the sand or gravel. You need forms, say 100' of either 2x12, 2x8 or 2x4 depending on what you do with the perimeter. And a bundle of stakes to hold the forms in place. Plus tie wire for the rebar and either chairs or dobies.

We don't get frost heaves and our soil is non-expansive. If you have either situation you may need a lot more sand and gravel under the slab as much as 12", which would be 20 to 24 yards.

Next you need to hire a finisher, about $250 for the day around here, and he should have grade stakes for the center and a screed board for rough leveling.

If I did the prep work myself, I would budget $2500 and maybe have a couple of
Benjamins to put in my pocket at the end of the day.

Hiring the whole thing out will be more. I don't know how much more, I have never hired out a slab.

 

[Scotty370]

Maybe some help here: Concrete Calculator, Prices and Pouring Information - The Concrete Network

 

[ustmd]

In August I had a 16 x 24 slab, 5000 psi, all prep work, finishing etc included.

$3200.

One caveat--I was on a slope that had a 22 inch dropm so one corner is 6 inches above grade, the other is 28.

 

[gregfender]

A gravel floor is looking better and better:laughing:

Actually, I was figuring on between $2.5-3K...one benefit is the soil is very stable and the chance of frost heave is really low.

Dave, for a rank amateur, how difficult would you say the prep work is; ie. forms, digging footer, etc. I'm not a complete novice and can be pretty mechanical when necessary, but I'm a history teacher, not a rocket scientist like some folks...

thanks in advance for the tips/advice!

 

[crash325]

I am looking to put down a 20x30 concrete slab for a shop/shed I am going to build. Thickness will be 4". Have any of you folks had concrete work done recently and know a good ballpark estimate for a simple slab?

4" Is pretty thin for a shop slab, that's how thick a standard floor is. If you hire it out another 2" of concrete is not that much more $$$:confused2:

 

[CurlyDave]

A gravel floor is looking better and better:laughing:

Actually, I was figuring on between $2.5-3K...one benefit is the soil is very stable and the chance of frost heave is really low.

Dave, for a rank amateur, how difficult would you say the prep work is; ie. forms, digging footer, etc. I'm not a complete novice and can be pretty mechanical when necessary, but I'm a history teacher, not a rocket scientist like some folks...

thanks in advance for the tips/advice!

There is nothing about the prep work you can not do yourself. Your profile doesn't mention owning a tractor, which would be a great help, but is not 100% necessary.

Before you do anything on a slab you need the design of the building that will go on it. I can't emphasize this enough.

If you are putting a shed/shop on top of the slab, you really need to think through how you are going to build the structure. You are going to need foundation bolts at code-specified intervals along the edge of the slab, where walls go, and you may need shear panel tie-downs in some places. Foundation bolts are usually every 48" and one no more than 12" from the end of each mudsill.

If you need tie downs, they are different than the foundation bolts, and the two are entirely separate. You can not use a tie down both as a tie down, and as a foundation bolt -- you need a separate bolt.

You will need designed footers, not by gosh and by golly. You need to plan out where the doors go, and you need to know about electric power.

Do you need a ground rod? The best way is a Eufer rod, which is nothing more than a 20' long piece of 1/2" rebar in the concrete, with about 6" protruding above the slab. It should protrude directly under the electrical panel.

Get your shop/shed plans ready before you even think about pouring a slab. Even if you are going to wait years to build the structure. If you don't, you will inevitably find that the slab is not good enough for the structure, and you will need very costly upgrades to fix this problem.


Look on Craigslist or in a local paper for concrete finishers. Have a few come out to see the job, interview them and get bids. During the interview process ask them about site prep and what they think is necessary -- they know your local conditions, which I don't. I would go above and beyond what a finisher recommends, but they will put you in the right ballpark.


The only things that require real skill are getting the slab square, and getting it either level or sloped the way you want it. You would be amazed at how often this gets screwed up.

Enough for now. Ask more advice when you have the building planned out.

Dave

 

[Gary Fowler]

Most folks think that putting in a slab is just placing the forms and dumping in the concrete. It takes planning as Dave mentioned and knowledge of the building codes in your area. I see you are in NC so you may have to design for hurricane wind loads. I hired my shop and new house build by a professional contractor and even he contracts out the slabs to concrete specialists who have the right tools and experience to pour and level it properly. You will live with the consequences of a "come on over and help me pour some concrete and drink beer parties" for a long time.

In building design it is not done from the ground up. You have to know what is setting on it first then design the foundation to hold it and all the wind, snow and in some places earthquake loads that it may be subjected to. Your winter temps., ground water level, soil condition all will have to be considered for foundation preparation. Get some advice from a local builder on the slab design AFTER you get your shop design complete.

 

[handirifle]

Six months ago, I had a contractor do my shop foundation, and framing for me. The slab uses reinforced concrete, with 12x12 footing, and 4" slab. The footing on one side is nearly 36" high, because the contract was for 12" on grade, which is 12" buried, and in order to level the floor, on side had to come up. The inside was backfilled with compacted dirt, and then 4" of sand before the concrete.

Concrete, and labor were a total of $5 per sq ft. my shop is 24 x 30 so it was $3600 for the foundation. I paid a little extra, about $500 I think for the excavation work.

This is for the central coast region, of CA. He had also done my house for me about a year earlier, so that may have helped on the pricing. I did do the back filling and compacting, to keep costs down.

 

[Western]

I have got quotes for a 30'x40' shop as well, luckily I have a friend from church that will cut me a decent deal. $3.75 sq. ft. for turn key on the slab not including pad prep. $1.00 a sq. ft. to just pour and finish. with me doing everything else. Haven't yet decided which way I'll go.

Most of the quotes I have got have been between $4-$5 sq. ft. That's for everything excluding site prep of course.