ADU site prep and pad grading in San Bernardino
Verdemont Excavation connects San Bernardino owners building an ADU with one licensed excavation contractor for the pad, footings and trenches.
What the excavation side of an ADU includes
California law now lets most single family lots add an ADU, and many add a junior ADU too. The state housing department ADU page lays out the rules cities have to follow. Before framing starts, the ground has to be ready, and that is excavation work.
On a typical detached ADU that means clearing and grading the pad, digging footings to the engineer's depth, trenching for the sewer connection, and running power, water and sometimes gas from the main house. Drainage matters too. The city wants water carried to the street or a planter, never toward the neighbor.
What ADU site work costs
| Job | Typical range | What moves the price |
|---|---|---|
| ADU pad and footing excavation | $4,000 to $11,000 | Pad size, slope, backyard access width, compaction testing |
| House or garage pad, rough grade and compaction | $4,500 to $14,000 | Cut and fill volume, hillside keyway, soils report |
| Sewer lateral replacement, open trench | $4,500 to $12,000 | Run length, depth, clay or Orangeburg pipe, street cut |
| Utility trench, per linear foot | $25 to $70 | Depth, cobble, hand digging near lines, surface patch |
| Drainage swale or French drain, per linear foot | $35 to $95 | Depth, gravel and pipe spec, outlet to the street |
Every row comes from the full cost guide.
Sewer, septic and the utility trench
The sewer line is the part that surprises people. If the ADU sits lower than the main house or far back on the lot, the new line may need to be deep or need a pump. If the main lateral to the street is old clay or Orangeburg, replacing it while the yard is open saves a second dig later. On septic lots, County Environmental Health has to approve the extra bedrooms.
Utility trenches typically run $25 to $70 a foot, and running power, water and sewer in a shared trench where code allows is the easiest way to save money.
SB 9 lot splits
Senate Bill 9 lets many single family lots split into two and build up to two homes on each. The big older lots in Fontana, Rialto and Redlands are natural candidates. Site work for a split goes beyond an ADU: a second pad, a separate sewer lateral or septic system, separate utility services and access. Budget $12,000 to $30,000 for the excavation side on a typical split.
- 1
Plans and soils
Your designer draws the site plan. On slopes a soils report sets footing depth and compaction.
- 2
Permit and DigAlert
Grading is reviewed with the building permit. DigAlert marks existing lines.
- 3
Pad and footings
Clear, grade and compact the pad, then dig footings to the engineer depth.
- 4
Trenches
Sewer, water, power and gas trenches, inspected before backfill.
- 5
Final grade
Drainage set so water leaves the lot the way the plan shows.
ADU questions we hear
How much does site prep for an ADU cost in San Bernardino?
Usually $4,000 to $11,000 for the pad and footings. Sewer and utility trenches add $25 to $70 a foot. Sloped yards and narrow access push it toward the top.
Do I need a soils report for an ADU?
On flat lots many cities accept standard footing design. On slopes, near fill, or with expansive soil the city or the engineer will usually want one. Expect $1,500 to $4,000 for the report.
Can my existing sewer line handle an ADU?
Often yes if it is in good shape. A camera inspection, around $250 to $500, shows whether the lateral is sound before you tie a second unit into it.
Who pulls the grading permit for an ADU pad?
The grading for the pad is reviewed with the ADU building permit. The excavation contractor handles their part and files the DigAlert ticket.
Towns where this comes up most: Yucaipa, Redlands, Fontana, Rialto.
Get your ADU site work priced
The address, the job and a photo or two. One licensed contractor calls within one business day.