New Construction Sewer Hookup in Boise: Costs, Permits, and Process

Building a new home in Boise or adding an accessory dwelling unit (ADU) to your property means connecting to the city sewer system. The process involves more complexity and cost than most builders and homeowners expect, especially in light of the City of Boise's recent connection fee increases. This guide walks you through every step, from fee calculations to final inspection, so you can budget accurately and avoid delays.

Connection Fees Explained: Trunk Fees Plus Treatment Fees

All new connections to the Boise sewer system require payment of connection fees to the City of Boise. These fees fund capacity in the city's water renewal (wastewater treatment) infrastructure. Connection fees consist of two components: trunk fees, which fund the sewer collection system capacity, and treatment fees, which fund wastewater treatment capacity. Together, these are a one-time cost paid before the connection is made.

The City of Boise updated connection fees beginning October 1, 2024, for the first time since 2014. The increase is being phased in over three years to reach full cost-of-service levels. Both residential and commercial fees were adjusted, and they will continue to increase through 2026 and beyond. Contact the city at (208) 608-7150 for current fee schedules, as they change periodically during the phase-in.

Assessment Fees: When They Apply and How They Are Calculated

In addition to connection fees, some properties owe assessment fees. Assessment fees cover the city's cost of constructing the sewer pipe in the roadway and the service line to the edge of the right-of-way. They are based on the average cost of pipe construction, manholes, pavement restoration, permits, surveys, and inspections.

Assessment fees typically apply to: previously undeveloped lots being built on for the first time, existing lots being split into multiple parcels, and properties that have never connected to the sewer system. If your lot already has a sewer line built to the right-of-way from a previous development, you may not owe an assessment fee—only the connection fee. Verify with the city before finalizing your construction budget.

The Physical Connection: From Your Foundation to the Right-of-Way

The connection fee covers capacity in the city system but does not include the cost of physically building the sewer lateral from your home to the edge of the right-of-way. That cost is borne by the property owner and paid to your plumbing contractor. It typically includes trenching, pipe installation (Schedule 40 PVC at minimum 2 percent grade), bedding material, backfill, compaction, and surface restoration. The physical connection cost ranges from $3,000 to $10,000 or more depending on the distance from the house to the right-of-way and the depth of the city main.

Builder vs. Homeowner: Who Pays What?

In a new construction scenario with a builder, the connection fees and assessment fees are usually built into the home's purchase price—you pay them indirectly. However, verify this in your purchase agreement. Some builders list sewer connection as a separate line item or exclude it from the base price. For custom builds or owner-managed construction, you are responsible for paying fees directly to the city and separately hiring a plumber for the physical connection.

ADUs and Lot Splits: Special Fee Considerations

Accessory dwelling units (ADUs) have become increasingly popular in Boise, and each ADU that connects to the sewer system requires its own connection fee. If your ADU shares the existing lateral with the main house, the physical connection cost is minimal. If the city requires a separate lateral (which varies by situation), the cost increases significantly. Lot splits trigger assessment fees for the new parcels and require new connection fees for each parcel that will be developed.

Step by Step: Getting Your New Sewer Line Approved

Step one: Engage a licensed plumber and submit a plumbing permit application through the PDS portal with a site plan showing the proposed sewer lateral routing, depth, and connection point. Step two: Pay connection fees and any applicable assessment fees to the City of Boise. Step three: Once the permit is issued, your contractor installs the lateral per the approved plan. Step four: Before backfilling, request a city inspection. The inspector verifies material, slope, bedding, connections, and clean-out placement. Step five: After the inspection passes, the trench is backfilled and the surface is restored. The permit is finalized. Step six: Coordinate with ACHD if the connection requires work within the public right-of-way (encroachment permit required).

Frequently Asked Questions