20×30 is the ideal size for a range of buildings including large sheds, garages, small workshops, barns, shops, and more. But, if you’re putting in a metal building, you’ll need a foundation to ensure it stays stable, strong, and dry.
A 20×30 concrete slab is ideal as the base or foundation for a small metal building. In fact, a traditional slab-on-grade foundation is one of the cheapest bases you can choose for a metal building. This guide will go over the costs associated with installing one, including the cost of concrete, labor, and extra materials.
In most cases, the average cost of a 20×30 concrete slab is $2,400-$5,400, including all materials and labor. However, costs can go to over $6,000 depending on where you are and the cost of materials and labor. In addition, if you need a sub-base or other extras, you can expect your slab to cost more.
Why Use 20×30 Concrete Slabs?
A 20×30 concrete slab is the fastest and cheapest base you can choose for a metal building with similar dimensions. While you will want a 20’ 2” x 30’ 2” concrete slab for a metal building, you can put in a simple slab on grade for as little as $2,500 with everything included. That’s cheaper than almost any other foundation option, unless you opt for a simple packed dirt and gravel foundation – which you shouldn’t do for a metal building.
20x30x4 foundations are suitable for most applications for a building of the same size. For example:
- Storage area
- Stable
- Small barn
- Garage/equipment storage
- Workshop
- Small retail shop
- Small business headquarters
- Agriculture storage or activities
20×30 is also a popular size for metal building kits and you can often buy them, off the shelf, ready to install. Here, you’ll need a simple 4” thick concrete slab foundation with piers for each of the supports. In some cases, you can also skip the piers as the building is small enough to distribute weight over the foundation.
If you’re using the building to store agricultural equipment you may also want to use a trenched foundation. In addition, if you’re using the building as a home extension, you’ll have to use a 6” thick foundation to meet building code.
How Much Do 20×30 Concrete Slabs Cost?
The costs of your concrete slab will depend on several factors such as area, local cost of labor, cost of rental, and what type of foundation supports you need. The following chart outlines the most expected cost ranges for a 4-6′ thick foundation. That’s 7.41 cubic yards of concrete for a 4” foundation and 11.11 for a 6” foundation.
| Costs | Cost per Sq. Ft. | Low | High |
|---|---|---|---|
| Concrete | $1.28-$2.95 | $770 | $1,777 |
| Concrete Truck | NA | $600 | $1,400 |
| Reinforcing Mesh/Rebar | $0.50-$2.25 | $300 | $1,350 |
| City Permits/Inspections | NA | $100 | $1,300 |
| Forms | $0.06-$0.80 | $50 | $480 |
| Excavation & Sub-Base | $0.05-$1.50 | $75 | $900 |
| Labor | $2-$3.80 | $1,200 | $2,280 |
| Vapor Barrier | $0.05-$0.20 | $50 | $150 |
| Total | $5.24-$14.39 | $3,145 | $8,637 |
*Please note these costs were based on quotes at the time of writing in July 2023 and may be different at the time of reading. Actual costs are subject to location, time of year, and market. Please use these numbers as a basis for your own research.
In addition, some of the costs listed are optional for a small building. For example, you may be able to skip the sub-base and excavation. In addition, you may need minimal vapor barriers. Therefore, you’ll always want to look at your specific build and calculate costs accordingly.
20×30 Concrete Slab Price Examples (Calculator)
If you’re pricing out what you need to install a 20×30 concrete slab, you’ll have to look at your location. For example, the difference in labor costs between a rural area and an urban one can be 90%. You’ll also see major differences in costs between concrete from region to region.
For example:
- 3,000 PSI concrete with Portland cement and sand – $104-$160 per cubic yard
- Labor costs – $11-$94 per hour per person, for an average cost of $300 per day per person
- Grading – $75-$5,000 per acre depending on land elevation and excavation work needed
- Slab thickness – Aim for 6” thick for a garage or residential building. Everything else works with 4”. You can expect about a 30% increase in concrete costs for 2” of extra thickness.
So, if you look at the cost of your slab, you can predict something like:
- 4” concrete slab on grade in a rural area (flat) – $2,5445
- 4” concrete slab on grade in an urban area (flat) – $4,205
- 4” concrete slab on grade in a rural area (elevated) – $3,200
- 6” concrete slab on grade in an urban area (flat)- $4,805
Of course, actual specific costs will depend a lot on actual local costs, so it’s important to price things independently and locally.
Factors Influencing 20×30 Concrete Slab Costings
Costing a concrete slab will almost always depend on your location. All other cost factors are variable based on where you intend to build. That comes into play for materials availability, delivery costs, availability and cost per hour for labor, city planning costs, support and stability needed for the slab, and much more.
1. Material Costs
Material costs can vary a great deal from region to region. For example, the national average cost of concrete is $104 to $160 per cubic yard. That pricing mostly depends on the local cost of portland cement, electric, etc. In addition, while the chart above lists the truck rental and cement yardage separately, most construction companies will list them together.
However, in 2022-2023, the direct average cost of Portland cement in the United States is $130 per metric ton, meaning it costs more to buy cement today than at any time in history. Of course, national averages do not reflect actual local costs, so you’ll have to check local costs.
Material costs also depend on the PSI of your concrete. For example, most 20×30 slabs need 3,000 PSI concrete. It’s unlikely you’d need anything stronger.
You’ll also have to consider the thickness. For example, you add about 33% of volume to the concrete by increasing the thickness of the foundation by 2”. If you have soft ground and need a very stable base, you’ll increase material costs by a lot.
2. Cost of Labor
The cost of labor can also vary dramatically from region to region. For example, New York city labor unions typically keep prices at about $94 per hour for a laborer. This means that labor in a big, unionized city can cost as much as 10 times that of labor in a small rural area with plenty of people willing to work cheaply.
In fact, national average rates for construction labor are about $300 per day, per person. You’ll typically need a crew of 3-4 people for a 20×30 slab. That includes the driver, someone to guide the truck, and two people to rake and smooth the concrete as it’s poured. More people mean the work goes faster.
The lowest rates for this labor are about $10 per hour. This means that for the same job, you can expect to pay $40-$376 per hour depending on location, or $320 to $3,008 for the same job. The only thing that sets this is your location and what local labor costs.
3. City Permits and Planning Costs
If you’re building in city limits, you’ll have to apply for planning permission. However, that planning permission will include permits for the full building, which means costs can be rolled into the cost of the total building. However, you’ll have to apply for and get planning permission before you can put down your slab.
In most cases, you can expect costs to range from about $100 to over $1,300. Often, that will depend on your location as well as what kind of building you’re putting in. Agricultural building planning can cost from as little as 5 cents per square foot. On the other hand, if you’re putting in an office downtown, costs can be as high as $10 per square foot. In most cases, you can expect these costs to hover around $200 unless you’re in a very urban area.
City permits may also require you to do soil testing and site testing, which, depending on region, may cost up to $1,800. On average, a soil test starts from about $700. While you won’t always need this, you will have to check what’s required for your planning permit.
In addition, you’ll typically have to source a metal building and get the engineering plans before you can apply for planning permission.
4. Slab Thickness and Strength
In most cases, you’ll be able to get away with a 4” slab on grade with rebar and mesh reinforcement. Together, you should expect that to cost about $300 in rebar and mesh and about $1,500 in concrete including truck rental.
If you increase the slab thickness to a 6” base, for example if you’re building for residential purposes or for a garage or if you intend to have heavy equipment inside, those costs will go up by 30%.
If you’re opting for an 8” foundation, for example if you’re building on unstable ground, you may even have to double actual material costs.
5. Rebar and Mesh
Rebar and mesh reinforcement strengthen the concrete slab so that it is more stable and less prone to cracking. Mesh is also cheap, typically starting from about 50 cents per square foot – meaning you’ll average at $300 for a 600 square foot slab. In addition, you can expect that you’ll need at least some rebar, which typically costs $1.25-$2.25 per square foot.
Here, you’ll generally want to talk to your construction manager to determine what you’ll need. However, you can almost always calculate maximum total costs at about $1,115.
6. Site Preparation and Sub-Base
Best-case-scenario, you can simply grade (level) your build site and throw a concrete slab on it. That will mean building a simple wooden form (usually from about $75 in materials) and pouring concrete into it. However, if you have an area with elevation or if you need piles, you’ll also need excavation. If you pay for excavation, it’s typically $1-$5 per square foot. This means that if you’re putting your building into a hill, you can expect costs to be, at minimum, $3,000.
However, on average, you’ll get something closer to about $75-$300 – unless the site is currently unsuitable to build on.
In addition, if you have to raft the foundation by digging trenches, you’ll have to pay about $5+ per cubic foot as well. It’s unlikely that you’ll have to unless you have soil with poor drainage or if you have very soft ground and need the extra stability for your foundation. Again, you’ll need a site inspection to determine if this is necessary.
7. Optional Extras
There are always extras you can opt to have for your foundation. However, it’s unlikely that you’ll actually need them for a small building. For example:
- Concrete finishing (polishing, top layer, etc.) – $1-$5 per square foot
- Vapor barriers – An average of $50-$150
- Extra strength concrete – Up to $1,000 extra for the concrete
- Edges – $1-$5 per linear foot or $100-$500
Drainage, site inspections, walkways, and other extras are all also not included in these cost estimates. Therefore, if you want them, you’ll have to quote those costs separately.
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Our team is ready to help you quote and find the best deal on your concrete slab. We offer service in all 50 states and we can align your concrete slab production and metal building delivery to ensure you’re project is aligned at every phase.
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Rex Metal Buildings offers construction services and supply for concrete slabs and metal building kits in all 50 states. Get in touch with us today to see how sourcing your full construction from one company can help you save hassle and costs. And, we’ll help you get the best deal by reaching out to multiple suppliers in our network.