A concrete slab foundation needs footings in order to:
- Provide support to the walls of the building built on the foundation.
- Resist heaving and shifting due to freeze/thaw cycles
- Prevent water runoff from undermining the slab.
- Allow the concrete slab to resist cracking and splitting.
- Keep pest animals from burrowing under the foundation.
- To comply with most building codes.
In most cases, you can incorporate footings into your foundation by digging a 12–18-inch deep trench at the edge of your foundation and reinforcing it with rebar. Pour concrete into this trench at the same time you pour your slab to create a strong foundation.
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Why Do You Need Footings for Your Concrete Foundation?
Concrete footings are essential to building a strong, sturdy foundation. A shallow foundation slab will often deteriorate, damaging the structure built on top of it. Shallow slabs are prone to tilting, heaving, and cracking if you live in a region with cold winters. Even if you live in a warm region, water runoff from rain can easily undermine a shallow slab foundation. This results in a tilting foundation.
- Footings are essential to a durable foundation.
- Most building codes require foundations to have footings.
It’s important to note that most building codes require footings for any concrete foundation. When building a garage, home addition, and most other structures, it’s essential to create plans that include a proper foundation. This is a must in order to receive a building permit. You are also required to prove you’ve carried out the plans and poured a foundation with proper footings. Otherwise, your structure may be deemed illegal.
How Do You Make a Slab Foundation With Footings?
The exact requirements for a foundation will differ according to the building code in your area. However, incorporating footings into your concrete foundation is relatively easy. Here’s how to do it:
- Plan and excavate the area for your slab foundation. Dig deep enough to allow for 3 inches of gravel and 4 inches of concrete.
- Mark an area 18 inches wide along the perimeter of your foundation.
- Dig an 18-inch-wide, 21-inch deep trench so that the edge of your foundation will be thicker than the interior slab.
- Lay a vapor barrier of heavy duty plastic over the dirt in the trench and slab area.
- Pour 3 inches of gravel onto the slab area.
- Add 3 inches of gravel to the bottom of the perimeter trench.
- Place rebar in the trench. The rebar installation should be rated to meet building code. It should also be properly suspended so that it is not resting on the bottom of the trench.
- Place rebar and/or mesh on the slab area.
- Pour your concrete, filling the trench and the slab area.
- Smooth and finish the concrete foundation.
This system will produce a strong, durable foundation that resists cracking, settling, and undermining, regardless of soil conditions.
Do Slab Foundations Have Footings?
Almost all slab foundations you’ll come across have footings. However, some homebrew foundations that were not properly permitted or examined by a building inspector may have been poured without footings. However, these typically deteriorate quickly and cause problems to the structure built on top of them. By making a footing at the edge of the slab, the weight of the walls is supported by the thick footing, not the relatively thin slab.
What is Wrong With a Slab Foundation Without Footings?
Slab foundations without footings spell disaster for any structure built on top of them. In a best-case scenario, the slab will crack and heave, causing minimal damage to the building on top of it. In a worst-case scenario, the slab will tilt, break off in places, or shift drastically. This can cause serious damage to the building atop the slab.
- Slabs without proper concrete footers will crack, tilt, or shift.
- Buildings on top of plains labs can be damaged as the slab deteriorates.
- Pest animals make burrows under plain slabs. Footers repel burrowing animals.
A seldom-discussed drawback of concrete slabs without footings is their propensity to invite pest animals. Woodchucks, skunks, coyotes, and raccoons can easily burrow under a thin concrete slab. This not only brings pests to your yard but also contributes to an undermined foundation. A slab with a deep footing repels animals, since they’ll seldom dig deep enough to go beneath the footing.
Can You Pour Concrete Directly On Dirt?
You should never pour concrete directly onto a dirt surface. Concrete poured in this manner is extremely prone to cracking and shifting. This is the cause of many tilted sidewalk sections and disastrous foundations. Additionally, concrete poured on dirt is prone to moisture damage that shortens the lifespan of the concrete.
- Do not pour concrete directly onto soil.
- Concrete on bare soil is prone to heaving, shifting, and cracking.
- Pour a 3-inch-thick base of gravel over soil, then add concrete.
- A gravel base adds durability to your concrete foundation.
Concrete should always be poured over a gravel base. A 3-inch base of gravel absorbs the natural shifting of soil as the seasons change, protecting the slab from heaving. Additionally, the gravel helps water drain away, which keeps the slab moisture-free and intact.
Can You Pour a Concrete Slab Foundation Without a Footing?
In most municipalities, it is against building code (and thus illegal) to pour a concrete foundation without an adequate footing. Although footing width, depth, and reinforcement depend on the local building code and the type of building being constructed on the slab, it’s always essential to have proper footing when pouring a concrete foundation. A footing will support the walls of the building, as well as ensure the foundation does not crack, tilt, or heave.