Basement ADU conversions for Seattle and the Eastside.

No. Three key requirements: ceiling height (most cities require 7 feet minimum, 7.5 feet in living areas), egress windows in any bedroom (specific dimensions and well requirements), and a path for separate utilities (electrical subpanel, gas if applicable). Older basements with low ceilings, no windows, or shared mechanicals may need significant modification or may not qualify at all. We assess feasibility before any design work begins.

Up to 1,000 sq ft typically, same as DADU/AADU. Most Seattle basements are smaller than that, so the practical answer for most projects is 'as large as the existing basement.' Some homeowners bump out a small portion of the basement during the conversion to gain a bedroom or a kitchen footprint, which gets handled with the same permit.

4 to 7 months from signed contract to certificate of occupancy for a typical Seattle basement ADU. The breakdown is roughly 3 to 4 weeks of design, 2 to 3 months of plan-check at Seattle DCI, and 2 to 4 months of construction. Faster than DADU because we are working inside existing framing and foundation. Eastside cities can compress further.

Basement ADUs typically run 30 to 50 percent less than a comparable DADU because the foundation, walls, roof, and primary utility infrastructure already exist. The variables that move the bid most are: existing ceiling height (low ceilings may require excavation), egress window scope (cutting concrete for new wells), waterproofing condition (older basements often need remediation), and the new mechanical system (separate HVAC, separate water heater, dedicated electrical).

Yes to both. Insurance: most carriers require notification when you add a legal second dwelling. Premium typically goes up modestly. Property taxes: the new finished living area increases your assessed value, which raises your tax bill. The combined increase is almost always smaller than the rental income the unit generates. We walk through the math during the consultation.