We’ve spent weeks getting our garage foundation as perfect as possible, right down to the concrete footings. This process has taught us so much about building your own home, and in this article we want to explain what we did to set our entire homebuilding project up for success.
As the saying goes, ‘a home is only as good as its foundation. Okay, we aren’t sure if anyone’s said that before, but as first-time home builders in the midst of building a debt-free timber frame home, we believe it.
You might find our process makes sense for you, or you might choose experiment with a different method instead. Regardless, we think there is value in sharing our experience of how to make concrete footings.
The Importance of Concrete Footings in Home Builds
In building projects, concrete footings are one of the first steps to tackle. Like with human feet, they are what ‘grounds’ a house to earth.
Concrete footings are essential for quality concrete foundations, as they provide support for the whole structure. The importance of correctly creating your home’s footing can’t be overstated, as uneven footings may cause the building to come out unbalanced.
Most concrete footings contain rebar, which adds support by helping the structure resist movement from the soil underneath that can compromise concrete over time.
Types of Concrete Foundations
There are three main kinds of concrete foundations for building projects: T foundations, slab ongrade, and frost protected.
- T Foundations: This traditional foundation method is best suited for places where the ground freezes. The wide footings are placed below the frost line, and narrower walls are added on top. This size difference adds support to the base of the foundation where it needs it most. Usually, three separate pours of concrete are required to create this foundation. We used this style for our home and placed our footings deeper than the 24” inch frost depth to comply with building codes.
- Slab ongrade: This foundation style consists of a single layer of concrete, several inches thick, that is poured on a bed of crushed gravel. This slab is usually thicker around the edges to increase the footing, and wire mesh is often added to the concrete to add support and reduce the risk of cracking. This style is better suited for places where the ground doesn’t freeze, but it’s possible to add insulation to make it more suitable for all temperatures.
- Frost Protected: Frost protected foundations are designed to hold heat around the concrete footings to prevent them from freezing. They only work with a heated structure, and they require two sheets of polystyrene insulation (one outside the foundation wall and one at the base of the wall) to keep slab ongrade- style foundations from being vulnerable to colder temperatures.
Our Concrete Footing Specifications
How do you know how big you need to make your concrete footings? The bearing capacity of your soil makes a difference. The lower the bearing capacity, the wider the footing needs to be.
Thanks to our heavy clay soil, our concrete footings ended up being 8” thick, 24” wide, and with a 36×36 footprint. It was our goal to keep things simple, as this is our first home and we didn’t want to get fancier than we could handle.
A rough guide for sizing your concrete footings can be found here.
Step Footings
Step footings are concrete footings that are poured at different levels to maximize excavation space and minimize concrete costs. They are often required when a building is built on sloped ground (like ours) or doesn’t have a full foundation.
It wasn’t in our original plans to create step footings, but our concrete expert recommended that we put them in the front of the house because they would help us excavate less land and save money on concrete.
Adding step footings to the front also meant we avoided building a frost wall across the back half of the foundation. This is because the hillside is so steep that the concrete footings were naturally more than 24” below the surface, protecting them from frost.
Concrete Footing for Buttresses
Buttress walls are designed to provide extra support for walls by transforming horizontal pressure into vertical pressure on the concrete footings beneath them. Not only do they make it possible to create higher, thinner walls, but they improve a wall’s strength while requiring less concrete.
Because we have a daylight basement and a steep slope behind the house, our engineer recommended building a buttress to support the hillside in the back.
We prepared 20-inch concrete footings for the buttress, placed four feet six inches from the house.
Rebar Placement in Foundation
To reinforce the concrete in our foundation, we relied on grade 60 rebar. We placed two pieces on both the right and left sides of the footing, one part on top of the other and 3” in from either side.
This isn’t the standard way to do it, as most people use three pieces of rebar split into thirds, but our engineer recommended this technique instead.
Placing the rebar was a tedious process. We maintained at least 24 inches of overlap between each piece and tied the ends together.
Rebar is relatively inexpensive for a job this size, so we weren’t stressed about saving a few feet and made sure our foundation was extra secure.
We also placed grade 60 vertical rebar right as the concrete was setting during the pour. This let us secure the walls to the concrete footings and improve its structural strength.
What did we learn from this process? It’s beneficial to have a team of experts to guide you along and bounce ideas off of, even if you do the actual work yourselves. Also, have your rebar supplier cut it to size for you! It will save you hours of effort.
Concrete Footing Piers
Our foundation also required large pier footings to support its weight through the posts. These essentially worked to extend the size of the concrete footings to add strength and security.
It’s best to dig and pour all footings and piers at once, having rebar and anchor bolts on hand to reinforce everything.
In places with freezing winters (like us) concrete footings should extend at least 12 inches below the frost line, be a minimum of eight inches thick, and twice as wide as the post it supports.
Adding a few inches of gravel to the bottom of the footings before pouring concrete improves its longevity by allowing for drainage.
This article only touches on our experience of building concrete footings and a foundation for our debt-free homebuild.
