Test a Seattle Lot Before Choosing an ADU Plan

Seattle-area projects can fail for ordinary reasons. The wrong permit office may be used, or a current unit may not be in the records. A stock plan may conflict with a tree, or the sewer may be too low. Finding these facts early can save money, even when the answer is to change direction.

Confirm which local office handles the site

Do not rely on the mailing city. Find the parcel and check whether it is inside Seattle, another city or unincorporated King County. That answer controls the code, permit system, plan programs and staff contacts.

For a Seattle parcel, start with SDCI’s accessory dwelling unit guidance. For another permit office, move to the matching location guide and preserve the source date.

Describe the legal starting condition

Create a simple property history from assessor details, permit records and documents held by the owner. Find:

• the primary dwelling and number of recognized units.
• garages, sheds or other accessory buildings.
• additions or finished spaces relevant to a conversion.
• easements or recorded restrictions found in available documents.
• unresolved differences between records and what exists in the field.

Do not treat work with no permit record as approved building. Mark it for review by the correct expert or public office.

Compare three physical routes on the same sketch

Even when an owner prefers one option, test other practical choices. Compare a detached unit, attached addition and conversion. Draw the buildings, lot lines, yards, trees, slopes, parking and access on a rough site plan. Show where workers and machines could operate.

The largest open lawn is not always the easiest place to build. Materials may have no useful path to it. A utility trench may cross tree roots, or drainage may run through the planned foundation.

Record property limits before making the unit larger

The first plan does not need to maximize size. It needs to fit the known site. Ask whether the quote may interact with:

• environmentally critical areas or steep slopes.
• shoreline or flood review.
• significant trees and root zones.
• retaining walls and concentrated drainage.
• fire access or difficult emergency response.
• overhead or underground utilities.
• building activity beside an occupied dwelling.

For each open question, name the proof needed. It may be a survey, tree report, soil work, utility locating or a written City answer.

Investigate a conversion as a current building

A garage or basement is not automatically living space. An early inspection should check the slab, foundation, moisture, frame, roof and ceiling height. It should also check openings, insulation, fire and sound separation, and kitchen and bathroom utility routes.

If the team cannot open walls or floors yet, list an allowance for hidden conditions. State when the area will be opened and who will review it. The conversion guide covers this path in more detail.

Trace the main services

Locate the electrical panel and note known service capacity. Find the water entry and available shutoff details. Review side-sewer records where available and sketch the probable connection route. Find how roof and surface water now leave the site.

This is not final engineering. It shows whether the preferred location creates long trenches or driveway removal. It may also reveal a pump, service upgrade, tree conflict or access problem. Use the utilities guide for the next review.

Test pre-approved plans against the site

Seattle’s ADUniverse tool can help explore pre-approved DADU choices. At site check stage, compare the actual footprint, orientation, openings and foundation assumptions with the sketch. Record which site-specific drawings, permits and service work remain.

For Kirkland, Renton or another city program, use that permit office’s current terms. A plan reviewed in one city or county is not automatically portable to another.

Produce a choice table

The written result should place each plausible route in one of four categories:

Avoid a red or green sales score that hides the reason. The owner needs the facts behind the choice and a clear next step.

Know what the early site review includes before paying

Quotes vary. Ask whether the fee includes a site visit, measurements and record checks. It should state whether the team will place a unit on the lot, review utilities and contact public offices. Also ask for a written summary, the number of ideas and revision rounds, and whether another builder may use the sketch.

There is no single Seattle fee because the work differs. Compare deliverables rather than the label “site assessment.”

Move to pricing only with a stable basis

Before requesting detailed quotes, give each bidder the same facts. Include the ADU type, current sketch, expert reports, utility assumptions and finish level. List open questions separately. This keeps one bidder from leaving out work another included.

The cost guide and builder comparison turn that common record into comparable rows.