Can I Excavate Next to My Concrete Floor?

Slab Foundations

• Unless you have a monolithic slab foundation, meaning the slab was poured all at once, your foundation should have a footing hidden one or more feet beneath the soil. The footing, which extends a few inches outward from the foundation wall, is the depth to which you can dig. Monolithic slabs don’t have footings, but they have additional concrete reinforcement beneath the slab. Don’t dig deeper than the bottom edge of a monolithic slab.

Before You Excavate

• Call your local utility companies before you start digging. The water supply line and the sewer drain enter and exit the house below the ground. Other utilities, including gas lines, electric lines and cables may also lie beneath the ground. Within 24 hours of your call, most utility companies will locate their lines with ground paint so you can dig safely. If one or more lines or pipes are in the way, the utility company may assist in the dig.

Excavation Considerations

• If you have to dig below the depth of the footing or the bottom of the foundation wall, consult an engineer first. Soil at that depth provides support for your foundation, and removing or disturbing it can alter the pressure on the concrete, increasing the risk of cracking. If this is the case, a contractor can install temporary structural supports before you remove the soil.

After the Dig

• Just dumping soil back in the trench is rarely sufficient, because disturbed soil does not have the same compaction ratio as does undisturbed soil. The remedy is to backfill in “lifts,” which involves adding a few inches of soil to the trench and then compacting it before adding a few more inches and doing the same thing. To reduce the risk of wood-eating insect infestation, do not backfill soil closer than 6 inches from the bottom of your home’s siding.