How Much Does a 20×20 Concrete Slab Cost? The Ultimate Guide

Building a barndominium requires a number of steps, and one of the most essential being laying the foundation. If you’ve mapped out plans for a 20 x 20 barndominium, the next step on your list is likely going to be pricing it out to determine exactly how much this important step will cost you.

In this handy guide, we’ll take a closer look at how much a 20 x 20 concrete slab will cost for your barndo build, and help towards a clearer financial picture of your barndominium project.

Before we begin you may want to consider using a barndominium kit under 50k with your barndominium build. This can help you save time and money!

20×20 Concrete Slabs: An Overview

20x20 Concrete Slab - Foundation

The short answer to the question “How much does a  20×20 concrete slab cost?” is somewhere between $1,600 and $3,200, based on estimates which show the cost of barndo foundations ranging from $4 to $8 per square foot. However, there are a number of different factors which can affect the overall cost. 

Concrete slab foundations can be poured in a range of different thicknesses, and with a number of optional features. Typically, a concrete slab will have the following factors which can affect the final price tag:

  • A wood form, which will maintain the shape of the concrete as it hardens
  • A mesh inside the concrete to fortify its strength
  • A row of rebar surrounding the inner perimeter of the slab
  • 3,000 PSI (based on the typical depth of six inches)
  • Labor costs for contractors to install the foundation

How Much Does a 20×20 Concrete Slab Cost? A Breakdown

20x20 Concrete Slab - Laid Slab

As we mentioned before, based on the typical price of a 6 inch thick, 3,000 PSI slab, your foundation will run between $4 and $8 per square foot. 

However, if you’ve settled on a relatively stripped-down floor plan, or you’re building on a plot with hardy terrain, you may not need a slab quite so thick.

If you’re able to build your barndominium on a four-inch concrete slab, for example, you may be able to save up to 74 cents per square foot.

If, on the other hand, the conditions of your build mean you’re going to need a particularly sturdy foundation, then you may need to fortify it with thicker edges. If you opt for 12-inch thick edges to the slab, this will typically cost another $1 per square foot.

Two other options for strengthening your foundations are adding wire mesh or a vapor barrier.

With a typical foundation, a fiber mesh will be integrated into the concrete slab to reinforce the concrete, but a wire mesh can be used instead to give the concrete greater structural integrity. In most cases, this will cost an extra 40 cents per square foot.

A vapor barrier can be used to protect the barrier against the effects of moisture and condensation which can seep in through the surrounding earth.

If your foundation needs a vapor barrier, this will cost approximately 50 cents extra per square foot.

Cost Savings by Going the DIY Route

20x20 Concrete Slab - Setting

A residential concrete slab foundation with roughed in plumbing and radiant floor heating tubes. The floor heating system can be water or propane.

For the vast majority of people building a barndo, all the actual labor will be taken care of by experienced and vetted construction professionals. When you’re taking this approach, you’ll generally be looking at the total price range listed earlier in the post: $1,600 to $3,200.

However, if you have a background in construction yourself, or you’ve determined that you have the right resources and know-how to lay your own barndominium’s foundation yourself, then you’ll be able to shave off a fair portion of the cost.

With materials alone, the cost for a six-inch slab will be approximately $3.57 per square foot. A four-inch slab, which is also a relatively common choice for barndominiums, will cost approximately $2.83 per square foot, working out at a price range of $1,132 to $1,428 total.

When factoring in the other features that we listed above, however, your foundation could wind up costing significantly more.

With a vapor barrier, a wire mesh, and 12-inch thick edges to reinforce the strength of your concrete slab, you’ll need to account for an extra $1.90 per square foot for the final figure (bringing the total to approx. $4.73 to $5.47 per square foot). With these features included, the total will run between $1,892 and $2,188 for the entire slab.

Now, potentially knocking $1,000 off of the cost of building your barndo this early into the process is obviously an attractive concept. However, going down the DIY route also comes with major challenges.

Aside from vetting suppliers, you’ll need to erect the forms properly, install the mesh, and finish off the concrete surface with a power trowel yourself. Even minor mistakes in any of these phases can undermine the strength of the concrete, leading to disastrous results in the long run. 

Unless you have a professional working knowledge of laying concrete foundations (in which case you’re probably not reading this article!) then we strongly recommend hiring contractors to lay your foundations.

Wrapping Up…

We hope you find this price guide on 20×20 concrete slabs useful as you plan out and build your barndominium. For more guidance on building your own barndominium, be sure to check out the state guides, barndominium costs and insurance; and featured homes and design software if you prefer to try designing your own plan- all on!