Site prep, tree protection, utility trenching

What happens

Before any concrete pours, the site has to be:

1. Tree-protected. Fencing per the arborist plan, signed off by SDCI inspection if required.
2. Cleared. Anything in the building footprint goes; landscaping that interferes with trenches goes.
3. Trenched. Water service from the street to the cottage, side sewer from the city main to the cottage, electric feeder from the main panel to the cottage subpanel.

This is a line item worth pricing carefully — it varies more than most.

What drives trenching cost

• Long runs. A cottage at the back of a deep lot can mean 80–120 ft of trench.
• Tree avoidance. A Tier 2 tree's drip line forces detours, doubling the run.
• Rock. Capitol Hill, Queen Anne, and First Hill basalt show up at $150–$400 per linear foot in some accounts.
• Pavement restoration. If the trench crosses a driveway or sidewalk, restoration cost adds up.
• Side-sewer routing. The shortest path to the main isn't always permitted; routing around easements, neighbor structures, or shared driveways adds tens of thousands.

Cost

Typical: $10,000 – $20,000 for trenching alone. Difficult sites: $30,000 – $50,000+.

This is a separate line from the rest of the GC bid — ask for it broken out.

Coordination

Three trades and three permits all want trenches in roughly the same place:

• Side-sewer contractor under the SPU side-sewer permit.
• Plumber under the King County plumbing permit, for water service.
• Electrician under the SDCI electrical permit.

A good GC sequences these so trenches open once, all three trades land their work, then backfill happens once. Confirm that single-pass sequencing is in the GC's schedule before mobilization.