Stepped Concrete Footings
Footings are the most basic structural support for buildings in contact with the earth. For houses on a level building lot the footings are very simple and end up all at one elevation. However, for more complicated designs the footings end up changing elevations and therefore require a “step” in the grade. Stepped Footings allow depth of footings to transition from one elevation to another.
Uses for Stepped Footings
The picture above shows a standard stepped footing for a residential home located in the Northeast. In this example the footing transitions from one grade level down approximately 4 feet to a lower level. The lower level is needed in order to provide frost protection in an area with a walk-out type basement. This is very common in cold climates with walk-out basements.
Another use for stepped footings happens when there is a change in grade from one slab to another. In areas with difficult rock sites the basement might be stepped up (resulting in lower head room) in order to avoid costly ledge blasting.
How Stepped Footings Are Built
The example above is by far the most common approach to building stepped footings here in the Northeast. The stepped footings are built all at the same time with some fairly rough yet affective methods. The footing is built using the following method:
- The lower footing is formed with standard forms like the one shown at right. The footing forms extend all the way to the back of the slope under the stepped footing.
- The upper footing is also formed in the same fashion. However, the side forms are extended and cantilevered out over the lower footing forms until the end of the upper footing is at least 12 inches or so past the back of the earth slope. Sometimes the location of the vertical face is calculated so that normal width wall forms will fit from that vertical surface back to the next closest corner.
- Pieces of plywood are nailed over the gap between the two. Also pieces of metal banding are installed on the back of the stepped footing (against the soil) and the sides of the plywood. This helps keep the forms from pulling apart due to the pressure of the concrete. If you look closely at the pictures above you can see the loose banding after the forms were removed.
- Next a vertical piece of plywood is nailed between the forms to create the vertical front face of the stepped footing.
- Concrete is then placed in the upper and lower forms at the same time. Because the concrete is fairly stiff for footings it typically does not flow out through the lower form. In cases where that’s a problem a baffle is sometimes nailed to the top of the lower forms to stop that from happening.
As you can see from the photo stepped footings are not all that complicated. However, they do make grade transitions for foundations much easier.