How Much Concrete Do I Need for 40×60 Slab for a Barndominium (Full Cost)

How Much Concrete Do I Need for 40x60 Slab for a Barndominium
How Much Concrete Do I Need for 40x60 Slab for a Barndominium

Building a barndominium starts with laying the foundation right. While planning on the floor plans and costs, it is important to take into consideration the costs of laying the foundation on which your very barndominium will stand. A lot of factors go into determining these costs, and it starts with how much concrete slab you are planning to lay as the foundation.

On average, the amount of concrete you will need for a 40×60 slab for a barndominium will be $9,500 to $14,400. This calculation takes into factor the area of the slab, the cost of the concrete mix, and the national average of labor and materials you will need for the job.

A solid foundation is required so that the barndominium you build on top of it is sturdy, robust, and the site can take the slab’s weight and anything you place on top of it. To achieve this, a certain amount of cost is involved. Keep reading to find out what factors determine the concrete slab’s costs and how you can arrive at the numbers.

Why Is a Concrete Slab Necessary When Building a Barndominium?

A concrete slab builds the foundation on which a building would be constructed. This should be a very strong, load-bearing base and capable of carrying any weight from vehicles to the general items you would store in a household and a workshop area if you have one.

It is also considered to be the engineered foundation on which you will build your barndominium. It requires skillful utilization of the mechanics involved in pouring the concrete that will align with the soil and rock and general gradient of the land in which the concrete slab is being poured.

What Contributes Towards a Robust Concrete Slab?

A strong concrete slab should have at least a 3000 PSI (Pounds Per Square Inch) strength that comprises 75% of crushed stone and a thickness of 6 inches (15.2 cms). Adding a fiber mesh into the concrete is also a good idea as it helps with reinforcement. The concrete slab will also require a row or a double row of reinforcing bars around the perimeter. This, again, adds significant reinforcement.

Lastly, a skilled workforce is just as important as the quality of materials used and the techniques used to build the concrete slab. In the absence of high-quality labor, all the efforts made with procuring the right materials will be in vain.

What Does a Concrete Mixture Comprise Of?

Concrete reaches a 3000 PSI within 28 days after it has been poured. A good concrete mix usually consists of the following ingredients:

Concrete Mixture

All the ingredients need to be mixed in a rotating drum mixer, ensuring that all the components are thoroughly combined.

Often concrete and cement are used interchangeably to describe the material that helps build your foundation slab, but there is a significant difference between the two. Cement is merely an ingredient in concrete. Cement is used at the top of a pile of a mixture of gravel and other similar components that form the concrete. 

Cement pours used on their own, but that is for smaller applications such as building a sidewalk or a patio. Compared to concrete, cement’s texture is a lot finer, and it is vulnerable to cracking over time. There are many other advantages of having concrete slabs over cement.

Concrete offers added strength and a stable base over which you could build your barndominium. It can accommodate heavy weighted objects and vehicles without causing the foundation to crack. Concrete also does not crack or contract with the vagaries of the weather.

The Factors Contributing to the Cost of Concrete Slab

Generally, the cost of a concrete slab depends not just on the area you would like to cover, but also on the type of concrete you are going for.

Today, there are many options available in the market, such as regular concrete, self-consolidating concrete, polymer concrete, and even glass concrete. The price of each of them varies according to their attributes and the company manufacturing it. 

Other factors that affect the cost of concrete slabs also include the thickness of the slab and its edges, the radiant heat, and the general gradient of the land. The size of the structure that you are going to build on top of the concrete base and the finish type affects the cost.

Here is a graph that shows the average concrete slab costs for different constructions with figures that include the range from a low cost to the higher end of the spectrum. The cost of laying a concrete slab for a barndominium is similar to what’s shown for an average garage in the graph below. However, for a 40 ft (12.19 m) x 60 ft (18.29 m) concrete slab, the price may still go higher.

Image Source: Home Guide

Professionals recommend using precast concrete for your foundation slab, which is a tad bit costlier, but the National Precast Concrete Association vouches for its long-term benefits.

Variation in Costs

On an average, it costs around $6 to $8 per square foot for a concrete slab, but this cost varies due to a number of factors such as the concrete thickness, the brand, and the material, the local labor charges in the area, and the location of the project.

How to Calculate the Cost for Your 40×60 Concrete Slab Project?

Regular concrete is sold at $110 per cubic yard on an average. A cubic yard is approximately 27 cubic feet (0.83 square meters). To calculate how much concrete you will need for your project, you will need to:

  1. Calculate the length, breadth, and width of the area you plan to lay the concrete slab.
  2. Next, you will need to multiply the numbers.
  3. Divide the result by 27.

The above steps should give you the amount of concrete you will need for your project. You can add another 10% as a buffer if there is spillage and avoid any potential lack of the material mid-project.

For a 40 ft (12.19 m) x 60 ft (18.29 m) concrete slab, let us assume that you will need a 4-inch (10.1 cm) thick slab.

  1. You will first need to calculate the area in square feet by multiplying the length with the breadth.

40 ft (12.19 m) x 60 ft (18.29 m) = 2400 ft (731.52 m)

  1. Next, the 4 inches (10.1 cms) thickness needs to be converted to feet. That is:

4/12 = .33 ft

  1. You will now have to multiply the thickness in feet by the square footage to determine cubic feet.

2400 ft (731.52 m) * .33 ft (0.10 m) = 792 cubic ft (22.43 cubic m)

  1. In the last step you will need to convert the cubic feet to cubic yards by multiplying the result by .037.

792 cubic ft (22.43 cubic m) * 0.37 ft (0.11 m) = 293.04 cubic yards (224.05 cubic m)

In order to determine how many bags will cover for 293.04 cubic yards use this simple table to calculate:

Area Covered by Bag Yield
Ready Mix Concrete Bag (weight in pounds)Area Covered (in cubic yards)
40 (18.14 kg).011 (0.0084 cubic metre)
60 (27.22 kg).017 (0.013 cubic metre)
80 (36.29 kg).022 (0.017 cubic metre)

Alternatively, you could use this calculator and key in the dimensions to figure out how many bags you will need. Another source shows how the typical labor cost will vary depending on the thickness of the concrete slab.

Concrete Work Cost by Thickness
Thickness (in inches)Typical Cost With Labor (per square foot)

Data Source: Home Advisor

Yet another way to calculate the amount of concrete you will need in cubic yards is by doing the following:

  1. Divide the total area needed for pouring the concrete slab into smaller areas.
  2. Try to divide it up in such a way so that it retains a semblance to a finite geometric shape (as shown in the picture below).
  3. Calculate the volume of the area and multiply the thickness of the concrete.
  4. It is likely that you would have calculated the area in feet. At this point, you will need to convert it from feet to cubic yards. This will give you the number of cubic yards of concrete you will need.

Image: Improvenet

Factor in Cost of Building a Foundation Drain in Your Concrete Slab

All the hard work of ensuring that a proper concrete slab is reinforced for your barndominium can be put at risk if there is a possibility of water accumulation in the foundation. Having a good drainage system will allow the water to leave the foundation area without causing it damage.

Underground water retention and accumulation of the water from the rains are two of the biggest risks threatening the building’s structural integrity built on top of such foundations. Having a good drainage system along the perimeter will help mitigate this problem.

Therefore, it becomes imperative to have a great drainage system for your foundation. It may lead to a little extra cost, but it is crucial if you are looking at the long term benefits you can have from it. 

The Ardex Feather Finish Grey/Gray/Gris Self-Drying Cement Based Bag is a mold and mildew resistant blend of hydraulic and other cement that is especially helpful in avoiding damages in case there is water retention in the ground.

In this video, you will see how to waterproof your foundation by creating a trench and adding a pipe to have an effective foundation drainage system:

What Is the Difference Between Ready Mix Concrete and Regular Bagged Concrete?

Ready-mix concrete (RMC) is ideal for large projects such as a 40×60 concrete slab for a barndominium. These kinds of large-scale projects also include laying a foundation for a house, building a commercial sidewalk, etc.

A ready-mix supplier will be able to provide you with an estimate of the amount of concrete you will need for your 40×60 slab.  

Calculating the Amount of Material Required for Base Fill

One of the easiest ways to calculate the amount of base fill is to go to the Granite Construction calculator where all you will need to do is key in the length, breadth, and thickness of the slab you want to build and let the site calculate the cubic yards of concrete you will need for the purpose.

Having said that, it is important to remember to always have a margin of safety and order 10% additional material as a buffer to counter any problems due to underestimating the amount. 

When you are ordering concrete, the general rule of thumb is to order a certain amount extra for every cubic yard, as shown in this table below:

Buffer Amount of Concrete Required for a Project
Requirement (in cubic yards)Extra to Allow any Margin of error (in cubic yards)

Additional Costs to Keep in Mind

Aside from the costs of procuring the supplies and labor, other costs you need to bear in mind include any overtime service fee for the crew members, or any unwarranted flooding causing delay and more time and money on the project.

Other costs include staining and stamping the concrete. If you are staining concrete, you are basically painting it in different colors to increase the visual appeal of your barndominium. This costs somewhere between $4 and $8 per square foot (0.09 square meter). 

Stamped concrete mimics the look of cobblestone paths and can be achieved in a budget of $11 to $14 per square foot. Smooth finishes cost a lot lesser coming up to $4.50 per square foot.


Investing in good quality materials for a concrete slab will give you rich dividends in the future. Labor costs are additional, and allowing the amount of time it needs for the concrete slab to dry up will also help with securing a favorable end result. 

This means you should allow the concrete enough time to cure and dry before you begin your work on the walls and other above-ground projects on the barndominium site.