How long does excavation take for a new house?
The digging itself is short: one to two days for the basement and another one to two for utility trenches. It is spread over five to seven visits across roughly the first two months of the build, because most of the calendar time is spent waiting on the foundation and inspections.
The visits, in order
| Visit | What happens | Time on site |
|---|---|---|
| Clearing and access | Trees and stumps out, rock entrance pad, silt fence | Half a day on a cleared subdivision lot; one to three days on a wooded acreage lot |
| Topsoil strip | Top 4 to 8 inches stripped and piled for later | Part of the early work |
| Basement dig | Cut to footing depth plus 2 to 3 feet of working room | One to two days; add a day for rock or hauling all spoil |
| Waiting | Footings, walls, waterproofing, drain tile, inspections | Two to four weeks, hole open |
| Utility trenches | Water, sewer or septic, electric and gas conduits | One to two days |
| Backfill and rough grade | Fill around the walls, shape the lot to drain | One day once the foundation crew releases it |
| Final grade | Topsoil back, final swales, driveway base | Months later, after siding and gutters |
What has to be ready first?
- A site plan and foundation plan with elevations tied to a real benchmark. If the plans say "finished floor = 100.00" with nothing tied to the ground, the surveyor has to set one before the dig.
- Survey stakes. Corner pins for the house, plus offset stakes so the corners can be found again after the dig wipes them out. Do not dig off a tape measure from the property pin.
- An 811 locate and a building permit. Even a bare lot can have a gas main, water main, or fiber line along the road. The locate is free and takes three working days. The permit from Jefferson County or the city has to be issued before the dig. Our excavation permit guide covers who issues what.
- Erosion control. Silt fence usually has to be up before the ground is disturbed. See erosion control for Jefferson County lots.
What to know at each step
Topsoil. Topsoil settles as it rots, so it cannot stay under the house or driveway. Keep it in its own pile, apart from the basement dirt, or you may end up buying 40 tons of it for the lawn.
The dig. Much of the county sits on limestone. When the bucket stops on a rock shelf, a hydraulic hammer goes on and the day is billed differently. A basement produces a lot of dirt, and on a tight lot it leaves on trucks, which is a cost to ask about up front. Slab and crawlspace houses skip the deep dig but still need footings trenched to the depth your building department requires, commonly 30 inches or more in the St. Louis area. More on the basement excavation page.
The wait. If it rains hard while the hole is open, water in it is normal. It should be pumped out before backfill, never buried.
Utilities. Everything that enters the house below ground goes in before the hole is closed. Each line can mean a couple hundred feet of trench. Near an existing gas main or utility corridor, hydro excavation exposes the line before a bucket goes near it. See the utility trenching guide and new water line installation.
Backfill. Clean stone goes over the drain tile, then fill goes in a foot or so at a time so the wall is loaded evenly and nothing settles along the house later. Subsoil from the dig is fine; topsoil is not.
Final grade. Topsoil is spread, final swales are cut, and the driveway gets 4 to 6 inches of compacted crusher run, whether it will be gravel, asphalt, or concrete. See grading and the land grading cost guide.
What makes it cost more?
| Factor | Cheaper | More expensive |
|---|---|---|
| Lot | Cleared, flat subdivision lot | Wooded, sloped acreage with stumps to haul |
| Foundation | Slab or crawlspace, footings only | Full basement with walkout |
| Rock | None inside dig depth | Limestone shelf at 5 ft, hammer billed hourly |
| Dirt | Stockpiled and reused on site | Every load hauled off, clean fill brought back |
| Utilities | Short runs, sewer at the lot line | Long runs, road bore, septic field |
| Access | Machines drive on from the street | Lowboy trailer needed, mud season |
On an easy lot the dirt work is a modest share of the build. On a rocky, wooded, sloped lot it can approach what the foundation costs. The Missouri excavation cost guide has ranges by task.
How do I get an accurate bid?
Send the site plan and foundation plan, not just the address. Say whether the lot is cleared and whether dirt should stay or be hauled. Ask for the visits priced separately, and ask how rock is handled and at what rate. Confirm who calls 811 and who pulls the permit; on an owner-built house, that is you.
Common questions
How much dirt comes out of a basement?
Roughly 500 to 800 cubic yards for an average-size house with a full basement, including the overdig. Some is reused as backfill; the rest is stockpiled and worked into the final grade on a large lot, or hauled off on a tight lot.
What if we hit rock during the dig?
In Jefferson County a limestone shelf inside the dig depth is common. The excavator switches to a hydraulic hammer and breaks the rock in place, then loads it out. Hammer time is typically billed hourly on top of the excavation, so ask any bidder how rock is handled and at what rate.
Sources
- Jefferson County, Residential Building Permit Application Checklist: a new home permit requires a site plan showing where the house sits and its distance to every property line, plus a foundation plan.
- Missouri Revised Statutes, Section 319.026: state law requiring notice to the one-call center before excavating.
- OSHA, 29 CFR 1926.651, Specific excavation requirements: the exact location of underground utilities must be determined by safe means as digging approaches them.
- Missouri Department of Natural Resources, Construction Land Disturbance: construction that disturbs one acre or more needs a land disturbance permit with erosion and sediment controls.