How to Excavate for Footings
Layout, excavation, and inspection steps for footing trenches and pad excavations before forming and pouring concrete.
Step-by-Step
- 1
Set up batter boards
Install batter boards at each corner of the building, set back 3–4 feet from the actual corner location. Stretch string lines between batter boards to represent the outside face of the foundation walls. Check for square by measuring diagonals — they must be equal.
- 2
Transfer layout to ground
Use a plumb bob to transfer the string line intersections to the ground at each corner. Mark the footing outline on the ground with marking paint. The footing is typically wider than the foundation wall — add the overhang dimension on each side.
- 3
Excavate to frost depth
Dig below the frost line for your climate zone. Check local building codes for the minimum footing depth — it ranges from 12 inches in warm climates to 48 inches in northern states. Keep the trench walls vertical and the bottom level.
- 4
Check the bottom conditions
Probe the bottom of the excavation with a rod or bar. The soil should be firm and undisturbed. Any soft, wet, or organic material must be removed. If you hit unexpected conditions, stop and call your engineer before proceeding.
- 5
Clean up the trench
Remove all loose material from the trench bottom. If the bottom is muddy from rain or equipment, let it dry or place a 2-inch mud mat (lean concrete) before forming. Never pour footings on wet or disturbed soil.
- 6
Call for inspection
Most jurisdictions require a footing inspection before concrete is placed. Call the building department when the excavation is clean and any rebar is in place. Have the plans on-site for the inspector.
Pro Tips
- → Dig 6 inches deeper than you need — it's easy to add gravel back, hard to remove concrete that's too low.
- → Photograph the excavation bottom and rebar before the pour — your documentation if questions arise later.
- → Cut footing excavations slightly wider than the form to give yourself room to set and brace the forms.
Watch Out
- ! Never enter an unsupported trench deeper than 5 feet. OSHA requires shoring or sloping for trenches over 5 feet deep.
- ! Call 811 before any digging. Utility strikes are expensive, dangerous, and always the excavator's legal liability.