Map the Connections Before the Seattle ADU Price

Two similar units can have very different site costs. Distance, slopes, mature plants, paving, access width and utility capacity all matter. Check these conditions on site before treating the price as fixed.

Create a single site-services sketch

Ask the team to draw the current and planned paths for power, water, sewer, rainwater and internet. The sketch should also show buildings, lot lines, trees, walls, paving, gates and the construction path.

Label what came from records, what was observed and what still requires locating or testing. A line on an old plan is evidence to investigate, not permission to excavate.

Electricity: calculate before selecting equipment

An ADU adds cooking, hot water, heating, cooling, lights and outlets. It may also add car charging. Have a qualified person record the current power service and calculate the new demand. The result may show that the panel or main service needs work.

Ask whether the quote includes trenches, conduit, wires, panels, meters and connections. Add repairs to every damaged surface. Seattle City Light publishes current rules, but the team must apply them to this design and property.

All-electric equipment choices can interact with the energy design and available capacity. Make those choices together rather than allowing the architectural, electrical and mechanical plans to drift apart.

Water: check route, capacity and ownership

Record where water enters the property, the meter and the likely branch point. Draw the new line and label its size, safeguards and valves. Note any main-house work. Low pressure or old private pipes may need more review.

The written list of work should say who plans with Seattle Public Utilities, who pays utility or agency charges and who repairs paving, planting or interior finishes. A broad “water connection” line does not answer those questions.

Sewer: confirm elevations early

Sewer drainage depends on real heights and a workable route. Mark the fixture level, connection point, pipe path and cleanouts. Show why gravity flow should work. Assign each open question to a person and due date.

Also assign permit, inspection and repair duties. King County’s wastewater capacity charge may apply to new homes in its service area. Check the current rule and bill directly with the agencies in charge. Do not hide it in a broad allowance.

Garage conversions need special attention because an existing slab and door threshold were not necessarily set for dwelling plumbing. Detached units at the rear of a deep or sloping lot may face a different route problem. Neither condition should be priced from floor area alone.

Stormwater: design for the finished site

A new roof, paths and changed slopes affect rainwater. Show where roof water is collected and released. Add final ground levels and protection for both homes and nearby property. Plan drainage with the foundation and yard work.

Seattle rain makes temporary controls part of the building plan as well. Ask how excavations, stockpiles and exposed soil will be protected, and who restores the site after trenching and heavy access.

Access can shape the building method

Measure gates, side yards, overhead space, slopes and turns. Mark delivery stops, storage areas and machine access. Tight access can change digging, concrete work, waste removal and labor.

A contractor’s price should state the access basis it used. If crane use, street occupation, hand excavation or small equipment is assumed, that belongs in the work rather than in a future surprise.

Trees, walls and neighboring edges

Tree roots, canopies, retaining walls and lot lines can affect the final plan and the work area. Mark protected features and get expert help when needed. A short trench is not better if it harms a tree or wall.

Plan neighbor-sensitive logistics such as work hours, temporary fencing, dust control and keeping shared access clear. These are operational details. But they influence whether the planned method is realistic.

Price repairs after construction as real work

Utility bids may cover the connection but leave out repairs. List any concrete, asphalt, decks, fences, gates, steps, walls, soil, lawn, plants and indoor finishes that must be restored.

Describe the expected finish instead of writing only “patch as needed.” Photograph the area before work begins. Agree on who will decide whether the final repairs are acceptable.

Separate four kinds of cost

For each service, divide the budget into:

1. Review and design.
2. Utility or public-agency charges.
3. Building and connection.
4. demolition, access and reinstatement.

Then mark each number as a fixed inclusion, measured quantity, allowance or owner-direct payment. This makes the ADU cost plan more useful and lets competing quotes be normalized.

Close unknowns deliberately

Keep a utility list with each question, current guess, person responsible, proof needed and due date. Check major unknowns before the owner relies on a total price.

If an unknown genuinely cannot be closed, describe how its cost will be decided. A transparent unit rate or agreed choice rule is stronger than an undefined extra budget for surprises held by the contractor.

Questions for a site walk

• Where will each service connect, and how was that point listed?
• Has planned demand or capacity been calculated?
• Which agencies must review or perform work?
• What surfaces and landscape will be disturbed?
• Does the price include removal and equivalent reinstatement?
• What work access has been assumed?
• Which utility conditions are still provisional?
• Who bears the cost if the field condition differs?