A foundation, by its very meaning, must provide support for the entire structure you're building. A garage footing must carry the weight of the walls and roof, and handle the force of wind and weather. The structure will only be as good as the footing it sits on, so adhering to local building codes with regard to the depth and the height of the concrete footing is essential.
Obtain a building permit from local authorities. Check for local codes regarding the depth you must dig when placing the footer. In most cases, the footer must be below the frost line. The depth of the concrete will be either 8 or 10 inches. If your site is on a hill or if the soil is poor, you may need a stronger foundation than a simple footing.
Clear and scrape the site, freeing it of all debris. Dig a trench 2 feet wide, and to the recommended depth. Add 2 feet on either side to give you room to work. The total trench area should be 6 feet wide. The ground should be slightly moist, but not wet.
Dig a trench under the foundation for any utility access lines. Place a PVC pipe in the trench.
Pound stakes into the ground where you want the outside and inside edges of the footing.
Use 2-by-10 boards to build the perimeters of the footing. Set the boards on the vertical and nail them to the wooden stakes.
Insert rebar or chicken wire inside the form. This will add 40 per cent to the strength of the footing. Prop the rebar off the ground using wooden blocks 1.5 inches tall. Attach these blocks to the rebar using metal wire.
Nail 2-by-4s at 6-foot intervals across the top of the 2-by-10s to strengthen the form and to prevent it from bowing during the concrete pour.
Pour the concrete. Spread it with a shovel and finish with a trowel for a smooth topside. Add anchor bolts where the walls will tie into the footing before the concrete sets completely.
Let the footing dry for several days before removing the forms and backfilling with dirt.