If you plan to build a concrete slab, you must know about footers. A concrete footer is crucial to any slab foundation, as it supports and stabilizes the structure. Your slab could settle, crack, or collapse without a solid foundation.
Footers are typically made of concrete and installed below the frost lines, the depth at which the soil freezes during the winter. The depth of the frost lines varies depending on your location, so it’s important to consult local building codes to determine the depth for your footer.
The width and thickness of the footer will depend on the size and weight of the structure it will support. Whether you’re building a shed, garage, or house, understanding the basics of footers for concrete slabs and foundations is essential.
In our guide, you can learn more about footers and concrete foundations. By the end, you’ll better understand how to build a solid foundation for your concrete slab on a grade or flat area that will stand the test of time. (Read Filling Gap Between Concrete Slab And Wall)
What is a Footer?
A footer is a concrete footing that provides a stable foundation for a building or structure. It is usually made of concrete with some kind of steel brace, like rebar, to provide added support once the concrete is poured. A pre-dug trench is filled with concrete, and the walls of a house or other building are built on top of it.
Footers are typically wider than the walls they support and are placed below the frost levels to prevent movement caused by frost heave.
Why Do You Need Footings for Your Concrete Foundation?
Footings are an essential component of any concrete foundation, providing support and stability to the structure. Without properly poured footings, your concrete foundation can settle, shift, or crack, leading to costly repairs and potential safety hazards.
Here are some reasons why footings are necessary for your concrete foundation:
- Preventing settling: Footings help disperse the weight of your structure, preventing it from sinking or settling into the ground. This is especially important in areas with troublesome soils, where the ground may shift or move.
- Supporting the foundation walls: Footings provide a solid base on top of gravel for your foundation walls, ensuring they remain stable.
- Protecting against frost heave: In cold climates, footings must be placed below the frost lines to prevent heave, which can cause the foundation to shift and crack.
- Complying with building codes: Building codes require that footings be constructed to specific standards, depending on the size and weight of the structure. This ensures the foundation is strong enough to support the load and withstand movement or settling.
How to Determine the Size of a Footer?
The size of a footer is an important consideration when planning a concrete slab project. In most cases, it is best to consult with a professional concrete crew or building inspector to determine the size of your project. (Learn How Many Wheelbarrows In A Yard Of Concrete)
When determining the size of a footer, there are several key factors to consider:
- Weight of the structure: The structure’s weight will determine the load-bearing capacity required for the footer. Heavier structures need wider and thicker footers to disperse the weight.
- Soil conditions: The soil’s bearing capacity will affect the footer’s size needed. Weak soils require wider footers to distribute the load over a larger area.
- Climate: Cold winters and frost heave can cause movement and cracking in concrete slabs. In areas with cold winters, footers should be dug below the frost levels.
How To Make a Slab Foundation With Footings?
When constructing a concrete slab foundation, footings are essential to ensure the slab foundation’s stability and prevent settling. Here are the steps to make a slab foundation with footings:
- Dig deep and level the ground where the slab will be constructed. The depth of the footing depends on the soil conditions, but it should be at least 6 inches deep and wider than the walls it will support.
- Create a form for the footings, which should be at least 8 inches wide, and 16 inches thickened at the edges. Ensure to include anchor bolts for attaching the structure to the footing.
- Pour the concrete footings onto your gravel, putting reinforcement in place if necessary.
- After the footings have cured, construct the forms for the slab, including any necessary insulation and vapor barriers.
- Pour the concrete slab, cure it, and properly control joint cracking.
How to Install a Concrete Slab Footer?
Prepare the Site
Before creating the footing layout, it’s crucial to prepare the site. Clear the area of any debris, vegetation, or other forms of obstructions.
Contact your local inspector to ensure you follow all building codes and regulations.
Creating the Footing Layout
Once the site is prepared, create a layout for the footing. Use spray paint to mark where you need to dig your trench. Ensure the lumber is straight and square it up before spraying a line about 8 inches on the outside perimeter of the box to represent the footing’s outer line.
Excavate the Footing Trench
Excavate the footing trench according to the layout. Dig deep enough to reach below the frost line to prevent frost heave. Ensure you create a thickened edge around the perimeter of the trench for added support.
Pour the Concrete Footer
After creating the footing layout and excavating the trench, it’s time to pour the concrete footer onto the gravel bed. Place wire mesh or steel rebar in the trench to reinforce the concrete. Pour the concrete into layers to prevent cracking, and control joints should be added to avoid movement.
Proper curing is essential for the concrete to dry and set correctly. In most cases, vapor barriers and insulation should be placed between the ground and the concrete slab footing, where the insulation prevents moisture and cold from penetrating the slab and gravel below. (Learn How To Clean Concrete Without Pressure Washer)
Footer Reinforcement Options
When constructing a concrete slab, a heated structure needs to have a solid foundation to prevent settling and movement. The footer is one of the most crucial components of a concrete slab foundation.
The footer sits below ground level and evenly distributes the structure’s weight across the soil.
- One option is wire mesh, a grid of thin steel wires woven together. The wire mesh provides additional strength and helps prevent cracking.
- Another option is to use rebar, a steel bar placed in the footer as a grid pattern. Rebar is an excellent choice for areas with poor soil, a slab on grade, or a slope.
Footer For Different Concrete Slabs
Footer for Basement Slab
The footer form for a basement slab is an essential component of the foundations. It provides a stable base for the walls and, ultimately, the roof. The footer should be constructed with a width of at least 16 inches and a thickness of 8 inches.
The form should be reinforced with steel bars or wire mesh, and a vapor barrier should be installed to prevent moisture from seeping into the basement.
Footer for Garage Slab
The footer for a garage slab is like that of a basement slab. It should be at least 16 inches wide and 8 inches thick, reinforced with steel bars or wire mesh, and dug deep enough to reach below the frost line. The footer for the concrete slab should also have a thickened edge to provide extra support for the walls. In addition, anchor bolts should be installed in the footer to secure the walls to the foundation.
Footer for Outdoor Slab
The footer for an outdoor slab on grade is typically less complex than that of a basement or heated structure slab. It should be at least 12 inches wide and 6 inches thick and dug deep below the frost line.
The footer should be reinforced with steel bars or wire mesh, and a layer of gravel should be added to the bottom to improve drainage. In areas with clay soil or if you need a slab on grade, a stepped footing or a trench footing may be required to prevent cracking or movement. A city inspector should be consulted to ensure compliance with local building codes.
Footer Inspection and Maintenance
Once the concrete footings for your slab-on-grade project have been poured and the slab-on-grade has been constructed, it is essential to regularly inspect and maintain the footer to ensure the longevity of your structure.
Here are some tips for footer inspection and maintenance:
- Regularly check for cracks or cracking in the footer. If you notice any, it is vital to address them immediately to prevent further damage.
- Check for movement in the footer. If you notice any indication, it is essential to consult with a professional to determine the cause and how to address it.
- Inspect the perimeter of the footer for any signs of settling or movement after pouring. This can show soil conditions or slope foundations issues that need addressing.
- Ensure that the buildings foundations forms are adequately supported and that the steel rebar or mesh reinforcement is intact.
- Check for proper curing and ensure that the footer was poured to the proper thickness and with the proper thickness of the thickened edge, and don’t forget the areas you’ll be putting doors.
- Regularly check for any signs of moisture or water damage around the buildings footer construction or slabs. This can show improper drainage or a lack of a vapor barrier in clay soil areas.
Can You Pour Concrete Directly On Dirt?
It is technically possible to pour concrete directly on top of dirt, but it is not recommended as the result can be uneven and unstable. Concrete poured directly onto dirt can settle unevenly, weaken, shift, and crack because of unstable ground and inadequate support or drainage. If possible, the ground underneath should be prepared before concrete is poured. (Learn How To Break Up Concrete With Chemicals)
In most cases, creating a solid foundation for your concrete slab is better by digging to a stable subsoil layer and constructing a proper footing or base. The footing or base for concrete foundations should be constructed with a thickened edge and support structures like steel reinforcement or wire mesh.
