How to Dig Out for a Basement

Set the first four stakes that represent the four corners of the house. The development plat, local codes and the floor plan all play a role in positioning the stakes.

Square the stakes by measuring from corner to corner. When the measurement from the front right corner to the back left corner matches the measurement from the front left corner to the back right corner, the stakes are square.

Run a string between the stakes to represent the foundation's perimeter.

Extend all stake lines by 10 feet. Since you can’t leave the original stakes in place and dig, because they would be in the way, you have to set permanent extended references. To do this, you'll need eight more stakes.

Imagine the current string lines as forming the center box of a tic-tac-toe game. To extend the lines, have two people hold a string, 20 feet longer than the distance between two stakes. Each person should stand 10 feet farther back from the respective stakes. When the strings align perfectly, drive two new stakes, 10 feet out from the original stakes. Tie a new string line between the extended stakes.

Repeat the process with the other three sides of the square and you’ll have a complete tic-tac-toe symbol represented by the strings. The new string lines should intersect directly over the original stakes.

Measure 30 inches out from the original stake line and paint straight lines on the ground with marking paint. This will form a rectangle 30 inches wider than the original stake line.

Tie construction flags on the extended stakes (there will be eight stakes) and remove the original stakes. Remove the strings from the extended stakes as well. Now the excavator can reach the line painted on the ground, which indicates the outside edge of the foundation hole.

Use a transit to set the foundation elevation. This is the level of the top of the foundation, and it's determined by the level of the lot at the curb and by subdivision codes. Drive a tall stake in the ground and paint a mark around the stake that represents the foundation elevation. The excavator will use this mark as a depth reference during the dig.

Excavate along the painted ground lines to the depth of the foundation walls. An experienced heavy equipment operator will dig a hole with straight walls and a level floor.

Tie strings on the extended reference stakes again. The strings will cross over the excavated hole. Use a laser level from within the hole to determine the exact points where the strings cross and drive stakes at those points.

Use ground marking paint to outline a box 8 inches wider than the box created by the stakes in the hole. Spray another line 24 inches inside of the painted line. These two lines represent the footings.

Remove the stakes from the bottom of the hole. The excavator will use a backhoe to dig the footing trenches approximately 1 foot deep and from line to line. Now you’re ready to pour footings.