How to Install Footings for an Addition

Determine the depth and width of the footings by looking at the construction drawings. This is done by looking at the drawings of the footings and reading the printed measurements. Calculate how far to offset the footings from the surveyor's corner pins. These metal stakes are placed on the outside edge of the foundation walls, and the footings must be in the center of these walls. Subtract the width of the foundation wall from the width of the footing. Divide the result by two to get the offset.

Hammer a wood stake into the ground the offset distance from the corner pin. Repeat this step for each corner. Tie string to the first stake and pull it to the second stake. Pull the string tight and secure to the second stake. This string represents the inside of the footing forms.

Build the footing frames using the lumber and wood stakes. Hold the lumber vertical along the string line and secure in place by hammering a wood stake on the outside of the lumber. Secure the lumber to the stake with three nails. Repeat this process to build the outside of the footing frame. Use a level to assure the footing frame is level with the ground. If it is out of level, remove some dirt from below the lumber with a shovel.

Measure the width of the footing and place a stake in the ground. Repeat this step to install a stake at each corner on the inside of the frame. Fasten a tight string line around these stakes.

Install the inside footing frames using the string line as a guide, this time placing the stakes on the other side of the lumber.

Lay a one-inch stake across the top of footings every five feet and secure with one nail on either end. This provides additional support once the footings are filled with concrete.

Install the required rebar in the footings according to the construction plans. The plans have a list of side notes that contain important information like required rebar size. Rebar is installed by laying it in a chair and securing it by wrapping wire around the chair and bar. This keeps the metal bars in the center of the footings.

Fill the footings with concrete to the height required by the plans. Use a concrete vibrator to assure it fills the entire forms and has no air pockets.

Work a screening board back and forth across the top to flatten the concrete. This levels the concrete and smooths its surface.

Trowel a v-shaped groove down the center of the footing around its entire circumference. This is called the "key". It prevents the foundation from moving side to side.