Home Additions in
Seattle
Expand Your Home Without Leaving the Seattle Neighborhood You Love. Our home addition contractors handle design, permits, and construction for a seamless result that feels like it was always there.
Why Seattle Homeowners Choose a Home Addition Instead of Moving
Stay in Your Neighborhood
Keep your kids in their schools, stay close to your favorite parks, and maintain your community ties.
Gain Space Without Moving Costs
Avoid exorbitant real estate agent fees, staging costs, bidding wars, and moving expenses.
Custom Lifestyle Design
Get exactly what you want—whether it's a massive primary suite, an open-concept kitchen, or a dedicated home office.
Potential ROI Increase
Adding square footage in Seattle's competitive housing market is one of the best ways to build significant home equity.
Solution for Growing Families
Adapt your current home for multigenerational living, new children, or aging in place.
Types of Home Additions We Build in Seattle
From a simple bump-out to a massive second-story addition, we design and build custom expansions tailored to your lot and lifestyle.
Second-Story Additions
Double your square footage without increasing your footprint.
Primary Suite Additions
Create a luxurious retreat with walk-in closets and spa-like bathrooms.
Kitchen Expansions
Push out the back or side to build the open-concept kitchen of your dreams.
Garage Conversion / ADU
Convert an attached or detached garage into living space or rental income.
Bump-Out Additions
Add a few feet to a room to drastically change how it feels and functions.
Room Additions
Add a new bedroom, sunroom, or dedicated home office to the main level.
Recent Seattle Projects
See how we've transformed homes across Seattle's neighborhoods with seamless, high-quality additions.
Second-Story Addition
Added 900 sq ft including 3 bedrooms and 2 baths, matching the 1930s craftsman style.
Kitchen Expansion & Bump-Out
Pushed the rear wall out 10 feet to create a massive open-concept kitchen and living area.
Primary Suite Addition
Built over an existing garage to create a luxury primary suite with Sound views.
Detached ADU
Converted an old garage into a modern 800 sq ft ADU for aging parents.
Transformations
Phinney Ridge Second-Story Addition
Transformed a cramped 1-story home into a spacious 2-story family home, seamlessly matching the original 1920s architecture while adding 1,100 sq ft.
Our Seattle Design-Build Process
We handle everything under one roof—from initial architectural concepts to final construction walkthroughs. One point of accountability.
Discovery & Consultation
We evaluate your home, discuss your goals, and review zoning and setbacks.
Feasibility & Budget
We provide a realistic conceptual budget based on current Seattle construction costs.
Design & Plans
Our architects design the addition, providing 3D renderings and structural plans.
City Permitting
We navigate SDCI, handling all permit submissions and city reviewer comments.
Construction
Our dedicated crews build the addition with strict quality control and weekly updates.
Final Walkthrough
We ensure every detail is perfect and hand over your industry-leading 5-year warranty.
Expertise in Seattle Permits, Zoning & Older Homes
Building in Seattle requires specific local expertise. From ECA (Environmentally Critical Areas) and tight lot line setbacks to structural requirements for seismic safety, the permitting process is complex.
Furthermore, many Seattle homes were built between 1900 and 1940. We specialize in matching historical trim, integrating new foundations with old, and upgrading electrical/plumbing systems seamlessly.
We Handle 100% of the Red Tape
You never have to visit the Seattle Department of Construction & Inspections (SDCI). We handle all drawings, engineering, permit applications, and inspector coordination.
How Much Does a Home Addition Cost in Seattle?
Every home and lot is different, but here are realistic starting ranges based on recent construction costs in the Seattle area for premium design-build execution.
Bump-Out / Room
Main floor expansions, sunrooms, or ground-level bedrooms.
Primary Suite / Kitchen
Large custom kitchen expansions or luxury primary suite additions.
Second Story
Full level additions requiring significant structural engineering.
* Pricing varies wildly based on site access, soil conditions, age of home, and finish material selections. These are broad ranges, not fixed quotes.
Get a Custom Estimate for Your HomeWhy Seattle Trusts 12th Ave Contractors
We aren't just another home addition contractor. We are a specialized design-build firm focused strictly on premium residential additions, room expansions, and major remodels — built to last, on time, on budget.
About 12th Ave — Home Additions Contractors Seattle
12th Ave Seattle is a family-owned design-build company founded by Ihor Maksymov. With over a decade of hands-on experience in residential construction across the greater Seattle area, we've built our reputation one addition at a time.
As dedicated home addition contractors, we specialize in second-story additions, primary suite expansions, kitchen extensions, ADUs, and full-home remodels. Every project includes in-house design, full permitting, and expert construction — under one contract, with one point of contact.
Our licensed, bonded team of builders and carpenters is experienced in Seattle's unique housing stock — from Craftsman bungalows in Fremont to mid-century ramblers in Bellevue — ensuring your addition blends seamlessly with your existing home.
Our goal is simple: to create spaces where Seattle families feel truly at home. We deliver high-quality craftsmanship, honest pricing, and transparent communication from the first consultation to final walk-through.
What Our Clients Say
"The design team figured out a way to give us the open kitchen we wanted despite a weird property line setback. Construction was clean and the communication was stellar."
"Adding a second floor is terrifying. 12th Ave made it feel easy. They handled the city permits flawlessly and the new floor matches our 1920s craftsman perfectly."
"Our project manager was incredibly responsive. The finish carpentry in the new bathroom is museum-quality. Highly recommend."
Home Addition Contractors Serving the Greater Seattle Area
Our home addition contractors work exclusively across the greater Seattle metro, giving us deep expertise in local zoning codes, permit timelines, historical housing styles, and neighborhood character.
Frequently Asked Questions
Ready to Expand Your Seattle Home?
Contact us today to schedule a free, no-obligation consultation at your home. We'll discuss your vision, review your property, and provide a clear path forward.