ADU Construction & DADU Design-Build in Seattle & the Puget Sound
ADU construction for attached units, detached ADUs and backyard cottages in Seattle and the Puget Sound, with design-build delivery and Passive House performance available.
Seattle & Puget Sound ADU Construction
Love Construction carries attached ADU construction and detached DADU projects from early site and zoning review through design, permitting, construction, testing and handover. For a plain-language explanation of the terms and the practical differences between attached and detached units, read our ADU vs DADU guide for Washington homeowners.
- Feasibility: property, zoning, setback, lot-coverage and utility review.
- Design and permits: livability planning, energy modeling and permit coordination.
- Construction: high-performance building, testing and move-in-ready handover.
About Our ADU & DADU Construction Services
Seattle’s ADU-friendly zoning makes it one of the best cities in the country for backyard cottages and Detached Accessory Dwelling Units (DADUs). Love Construction builds ADUs to Passive House standards, super-insulated, airtight, and incredibly efficient, so your rental unit, guest house, or aging-in-place suite costs almost nothing to heat and cool. These small, efficient buildings are the perfect canvas for Passive House construction: manageable budgets, incredible performance, and they pay for themselves through rental income.
- Detached ADUs (DADUs) and backyard cottages up to 1,000 sq ft
- Attached ADUs including basement conversions and garage conversions
- Passive House performance with ultra-low energy costs
- Full kitchens, bathrooms, and living spaces designed for independent living
- Aging-in-place design with accessible features and single-floor layouts
- Rental-ready finishes with separate entrances and utilities
Our ADU & DADU Construction Process
Site & Zoning Review
We evaluate your property for ADU feasibility, review zoning requirements, setbacks, lot coverage limits, and utility connections.
Design & Energy Modeling
We design your ADU to maximize livability within the allowed footprint while achieving Passive House energy performance.
Permitting
We handle all City of Seattle permits, including building, mechanical, electrical, and plumbing. We navigate the ADU-specific requirements.
Passive House Construction
Our crew builds your ADU with the same precision and attention to airtightness and insulation as our full-size Passive House projects.
Testing & Handover
Blower door testing, energy performance verification, and complete walkthrough. We hand over a move-in ready space with your 5-year labor warranty.
ADU & DADU Construction Service Areas
We provide adu & dadu construction services throughout Seattle & the Puget Sound. Click on a location to learn more about our services in your area.
Frequently Asked Questions
Do you build both attached ADUs and detached backyard cottages?
Yes. Our ADU/DADU construction services include attached units such as basement and garage conversions as well as detached backyard cottages. If you are still deciding which format fits your property, start with our ADU vs DADU comparison guide.
How much does an ADU cost to build in Seattle?
ADU costs in Seattle vary by type. Attached ADUs often range from $85,000-$280,000 depending on the existing basement, garage, or addition scope. New DADUs commonly range from $175,000-$550,000 depending on size, site access, utility work, finishes, and whether Passive House performance is included.
How long does ADU construction take in Seattle or King County?
Attached ADUs commonly take 8-12 months from contract to certificate of occupancy. New DADUs often take 12-18 months because they require separate foundation, utility, structural, permit, and inspection work. City review time varies by Seattle, SeaTac, Bellevue, Kirkland, Renton, and other King County jurisdictions.
Can Love Construction handle ADU zoning review and permitting?
Yes. We review the property for ADU feasibility, zoning requirements, setbacks, lot coverage and utility connections, then coordinate the building, mechanical, electrical and plumbing permits required for the project.
Can a Passive House ADU really have near-zero energy costs?
Yes. A well-built Passive House ADU in Seattle’s mild climate can have total heating and cooling costs under $20/month. Many of our ADU clients add a small solar array to achieve true Net Zero.
Ready for Your ADU & DADU Construction Project?
Contact Love Construction today for a free consultation.
Plan the Seattle-area construction scope carefully
Love Construction projects work best when the owner, designer, and builder begin with the same scope, site constraints, access expectations, and decision timeline. Before comparing options, gather the property address, photos, existing drawings if available, notes about utilities and structural changes, and the rooms or exterior areas affected by the work. Confirm which decisions are already approved and which still need pricing, design, or permit review.
For additions, remodels, ADUs, DADUs, new construction, seismic work, and custom interiors, the practical details matter as much as the finish list. Document parking, staging, delivery access, occupied areas, neighborhood constraints, utility shutoffs, and any work that must stay separated from family routines or tenant operations. A clear early brief helps the construction team identify what can be priced from current information and what requires additional drawings, engineering, product selections, or jurisdictional feedback.
Coordinate selections, permits, and handoffs
Keep product selections, plan revisions, finish schedules, change requests, and owner approvals in one current record. Seattle-area construction can involve design review, structural coordination, energy details, inspections, utility coordination, and schedule dependencies between trades. When a choice changes cabinets, windows, fixtures, appliances, layout, framing, or exterior openings, review the connected cost and timing impact before field work depends on the prior version.
At each handoff, confirm the active plan set, open questions, owner-supplied items, inspection status, site access, and the next decision needed. Good construction communication is specific: who owns the item, what information is missing, when it is needed, and what work depends on it. That record protects the project from assumptions and gives the homeowner a practical way to track progress.
Keep construction decisions tied to real field conditions
Before work begins, review how the planned scope connects to the existing structure, utilities, drainage, framing, foundations, finishes, and occupied spaces. A remodel or addition may look simple on a room list while still depending on structural openings, mechanical routing, electrical capacity, weather protection, and sequencing between trades. The owner should know which decisions are cosmetic, which require technical review, and which cannot be finalized until hidden conditions are exposed.
For ADU, DADU, passive-house, new-home, and major remodeling work, the project record should separate confirmed requirements from allowances. Confirm access for crews and deliveries, storage areas, dust control, temporary protection, inspection windows, owner-supplied items, and any rooms that must remain usable. When the home is occupied, name the daily contact and decide how questions, photos, site changes, and approvals will move between the field and the owner.
Close each phase with a useful record
At the end of a design, preconstruction, rough-in, finish, or punch phase, record what was completed, what remains open, and which decision controls the next step. Keep permit notes, product selections, drawings, finish references, inspection results, change approvals, and warranty information with the project file. That habit makes future maintenance, resale questions, and later remodel phases easier to understand.
When a project changes, document the reason, affected scope, cost or schedule implication, and approved direction before the change is built into the work. That protects the homeowner and the construction team from relying on memory during a complex Seattle-area project.