How to Build a Footer for a Garage

Mark the inner edge of the footer on the ground with spray paint or wooden stakes.

Dig a trench for the footer working out from the edge you marked. The trench must be deeper than the frost line in your area. Unless you live in a warm climate with a shallow frost line, such as the southern U.S., you'll want to do this with a 1 1/2-ton excavator rather than with a shovel. Make the trench wide enough to fit the width of two concrete blocks placed next to each other plus 2 feet. The footer must be as wide as the two blocks, and the extra 2 feet allow for a drainage trench and room to maneuver inside the trench.

Construct the form for the footing by driving wooden stakes into the ground every 3 feet, about a foot in from each wall of the trench. Nail two-by-four boards to them. Measure and cut strips of two-by-two wood to fit across the form. Nail them to the top of the form every 3 to 4 feet to provide extra strength for the form as the concrete is poured.

Dig a drainage trench along the outer edge of the wooden form that is about 6 inches deep and 8 inches wide. Slope the bottom of the trench in the direction that you want the water to drain.

Pour about 2 inches of gravel into the drainage trench, and then place drain tile wrapped in landscaping fabric in the center of the drainage trench. Drain tile is perforated plastic pipe. Fill the rest of the drainage trench with gravel.

Place a level across the top of the form every few feet. If the form isn't level, tap the higher side of the form down with a rubber mallet until it is level.

Pour the concrete into the form. Depending on how big the footer is, it may be better to hire a concrete contractor to do the pour rather than do it by hand. The footer will be stronger if the concrete is done in one pour.

Smooth the surface of the concrete with a trowel. Allow the concrete to cure for at least 4 or 5 days, and then remove the form.