The key to any building project is starting with a solidly-built foundation. And while barndominiums are generally easier to construct than a traditional house, you still want to take your time laying the concrete slab foundation. So what is the best way to lay a concrete foundation for your barndominium?
To pour a barndominium slab, you’ll need to lay a bed of gravel on level ground, build the forms that will give your slab its shape, add the footers to keep the foundation stable, and finally pour in the concrete. Don’t forget to check local building codes first and get all the necessary permits.
If it sounds like a lot of work, don’t worry. I wrote this step-by-step guide to help you through every part of the process to get it done efficiently, so let’s jump right into it.
Building codes–also known as ordinances–are laws laid out by local regulatory authorities. They are made at the local level and are standards that both new and old buildings must meet to have legal occupants. These apply to every building, and not just residential homes.
What’s covered in building ordinances? That depends on where you live, but most building codes in the United States use the International Building Code, or IBC as a model. The IBC gives a baseline standard for local authorities to build upon.
The local building ordinance gives specific requirements for your barndominium, such as plumbing, electrical systems, and more. While all of it is useful to know (and must be followed, lest you run afoul of the law), for this step, we want to look specifically at any regulations involving the foundation.
Ultimately, you’ll need to get a building permit for your barndominium. To obtain the permit, you must outline your building plan in detail and submit it for approval. As long as you follow the ordinances, you’ll likely be approved.
The soil where you want to build is also important to consider. The National Association of Conservation Districts explains that soil quality can support or hinder a concrete foundation. In addition, poor soil can cause the building to sink, so have multiple locations in mind if one doesn’t work out.
Once you have your building permit in hand, you can start preparing for your foundation. This is a labor-intensive job, but determining your foundation’s size is easy. Unlike houses, barndominiums only require a concrete slab a few inches longer and wider than the structure itself.
And there may be a limit on the maximum size of a barndominimum, which you can learn more about in my other guide.
You also need to consider the thickness of the slab, which in turn will determine how deep you’ll be digging. You should plan for your slab to be at least four inches thick (10.16 centimeters). Note that this recommendation may change based on the size of your barndominium, so consult with a construction team to be sure.
When setting your pad, you may need to do some excavation work first to ensure the ground is level. Generally speaking, this is best done by professionals, as it may require the use of special heavy-duty equipment. Excavation is also an ideal time to test the soil for stability.
Finally, you’ll want to lay a bed of gravel in the excavated space that’s four inches (10.16 meters) deep (in addition to what you’ve dug for the slab already). Compress it so that the pieces have little room to move. The gravel bed will serve as the supporting layer for your concrete.
Think of the forms as a frame. When you pour concrete, it will continue to spread out until it reaches a barrier or crumbles. It also needs to be held in place while it dries, which can take one to several days, depending on the amount used.
Concrete forms are built above ground, matching the desired dimensions of your concrete slab. This won’t require any more digging, but you will need to do some construction. Thankfully, there are many materials that make excellent concrete forms, so it’s easy to find something that will fit into your budget.
Some of the materials you may want to consider for your concrete forms include:
The thing to remember about building concrete forms is that it’s more than just making a massive frame. It needs support to hold the drying concrete in place, which most materials can’t do on their own. Reinforcing forms is a combination of bracing beams together where they meet (securing them with smaller boards and nails) and using smaller boards to reinforce and prop up the forms from the outside.
Not surprisingly, this step requires a lot of precision. The forms being perfectly level and measured ensures the concrete can dry into the appropriate shape. Unless you’re a handyman, your best bet is to leave this to professionals.
Before you can start pouring concrete, you need to create a perimeter of footing inside the forms. The purpose of footing is to support both the foundation and the structure to minimize settling. To put it another way, the footing will help keep things stable.
The concrete footing is usually a foot-wide (3.28 meters) trench that runs around the interior of the forms. They run a foot (3.28 meters) deep and, because they are made of concrete, require their own forms to hold it in place.
However, your footing’s dimensions, including depth, depending on the soil’s quality and your barndominium’s dimensions. Your contractor team can make the appropriate calculations for you, so you won’t have to second guess your work. Like the forms, getting the footing right the first time is best.
A rebar is added to reinforce the trenches before the concrete gets poured. Construction needs to stop while you wait for it to dry. Once it has, it’s time to remove the footing’s forms.
With the footing in place, let specialists install plumbing and electrical work. This may take some time, but once they’ve finished, it will finally be time to complete the foundation.
With everything else in place, it’s time to actually make the slab by pouring concrete into the remaining space inside the forms. Again, there’s no need to rush here since the concrete will take at least a day to dry. However, you should take additional time to ensure the concrete is level before it dries.
Patience is critical when working with concrete. Dynamic Concrete Pumping lists “waiting too long to level after pouring” and “removing the forms too soon” as common mistakes. These errors are very difficult (and expensive) to correct, so don’t rush things.
Another reason you should take it slow when pouring concrete: personal safety. Wet cement that comes into direct contact with skin can cause severe chemical burns. Its dry form can cause irritation if it gets in your mouth or eyes, too, so always wear appropriate safety gear.
Any time you handle cement, you should be wearing the following safety gear:
- Full-length pants
- Long-sleeved shirts
Once the concrete is poured and dried, you can safely remove the forms. That’s it! You can now continue to the next step of building your barndominium.
Pouring a concrete slab is the first step to building your dream barndominium. However, it’s an incredibly labor-intensive process that requires careful planning to be performed correctly. The time you spend preparing will save you time, potentially fixing mistakes and repeating steps down the road.
You must carefully go over local building codes before breaking ground to avoid any problems. These regulations, together with the knowledge of an experienced professional construction team, will provide you with the best roadmap to get the job done. Remember to take your time and follow your experts to ensure a final quality slab.
Can I Use a Pre-Existing Concrete Slab Instead?
In most instances, a pre-existing concrete slab will not serve as a safe foundation for your barndominium. Since the barndominium was previously built, it may not meet current building codes in your area. It’s also difficult to ascertain how much weight it can safely support.
That doesn’t mean it’s entirely impossible, though. For example, if you’re attached to using a pre-existing slab, it’s still possible to have it evaluated by a building inspector or engineer. In some situations, you can modify the slab to make it suitable for a barndominium foundation.
Will the Frost Line Impact My Slab?
Outside of construction, frost lines have minimal impact on your home. However, they are almost always integrated into building codes, creating restrictions on how you can build foundations.
The frost line will most likely impact your slab. First, if you’re living in a colder region, you’ll need to dig your footing deeper than you might otherwise. Your footing must reach deeper than the frost line to ensure stability.
How Much Does a Concrete Slab Cost?
Ignoring the costs of labor and tools needed for installation, the cost of your concrete slab will depend on the slab’s size. Your concrete slab will cost between $4 and $8 per square foot. Based on this, you can take the estimated dimensions of your slab and come to a closer estimate.
Is Concrete the Best Option for Barndominium Foundations?
Concrete is the best option for barndominium foundations. When it comes to making a barndominium foundation, there is no substitute for concrete. No other material has the strength or durability to support a barndominium. In addition, other options will likely create an uneven base that could damage the supporting structure.
If you’re interested in learning more, I’ve compared slabs and crawl spaces with respect to barndominiums. I cover the advantages and disadvantages of both solutions.