Additions & ADUs
Expand your living space — room additions, second stories, and Accessory Dwelling Units.
● Licensed & Insured
● Family Owned
● Free Estimates
● Owner Supervised
Home Additions and ADUs in the Greater Seattle Area
Need more space without the hassle of moving? Northwest Custom Homes and Remodel specializes in home additions and Accessory Dwelling Units (ADUs) that seamlessly integrate with your existing home while adding valuable square footage.
Whether you need an extra bedroom, expanded living area, home office, or a standalone ADU for rental income or multigenerational living, we handle every aspect from design through permitting to final construction.
Why Homeowners Trust Us for Additions and ADUs
- Deep expertise navigating local zoning and ADU regulations
- Structural engineering that matches additions seamlessly to existing homes
- Full permitting services including DADU and AADU applications
- Energy-efficient construction meeting Washington State energy codes
- One team handles everything — foundation to finish
- Transparent budgeting with detailed cost breakdowns upfront
From Room Additions to Standalone ADUs
Our addition and ADU services include second-story additions, bump-outs, sunrooms, attached garages, in-law suites, detached accessory dwelling units, and garage conversions.
Every project includes foundation work, framing, roofing, siding that matches your existing home, full electrical and plumbing, HVAC, insulation, drywall, and all interior finishes.
Our Additions and ADU Process
Site Assessment
We evaluate your property, review zoning regulations, and discuss the best approach for adding space to your home.
Design & Engineering
Architectural plans are developed to ensure the addition integrates seamlessly with your existing home structure and style.
Permits & Approvals
We manage all permit applications, plan reviews, and regulatory requirements specific to your jurisdiction.
Foundation & Structure
Foundation, framing, roofing, and exterior finishes are completed to match and complement your existing home.
Interior Build-Out
Electrical, plumbing, HVAC, insulation, drywall, flooring, and all finishes are installed to create a complete living space.
Final Inspection
We conduct a thorough walkthrough and handle all final inspections to ensure everything meets code and your expectations.
Serving the Eastside and Greater Seattle
We serve homeowners throughout Kirkland, Bellevue, Seattle, Redmond, Bothell, Woodinville, Sammamish, Issaquah, Mercer Island, Newcastle, Renton, Kenmore, and Lake Forest Park.
As local contractors who live and work in the Pacific Northwest, we understand the unique needs of homes in our climate — from moisture management to energy efficiency upgrades.
Frequently Asked Questions
How much does a home addition cost?
Home additions in the greater Seattle area typically cost $300 to $500+ per square foot depending on complexity. ADUs range from $150,000 to $350,000+. We provide detailed estimates after our site assessment.
Do I need a permit for an ADU?
Yes. ADUs require permits in all jurisdictions we serve. Many cities on the Eastside have streamlined their ADU permitting processes. We handle all applications and requirements for you.
How long does an addition take to build?
A typical room addition takes 3 to 5 months. A standalone ADU usually takes 6 to 10 months including permitting. Timelines depend on complexity, weather, and permit processing times.
Will the addition match my existing home?
Absolutely. We take great care to match rooflines, siding, trim, and architectural details so the addition looks like it was always part of the original home.
Ready to Start Your Project?
Contact us today for a free consultation. Let us show you how we can transform your home.
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Additions & ADU Projects
