With over a decade of experience, we design and build ADUs and custom home additions that expand your living space, add value, and blend seamlessly with your home’s style.

Seattle Eastside Home Addition and ADU Building Professionals

Upgrade your home with a trusted Seattle addition contractor and ADU builder . Specializing in custom home additions, extensions, detached and attached ADUs, and energy-efficient upgrades, we provide exceptional craftsmanship and satisfaction from over 14 years of expertise.
4.9
Based on 37 reviews
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Professional Builder

5 Star Rated Seattle Construction Company

14

Years of
Experience

+150

Completed
Projects

FREE QUOTE FOR YOUR ADDITION OR ADU

Professional Addition & ADU Contractor
Seattle’s Eastside, WA

Our Comprehensive Addition & ADU Services Include

ADU Builder in Seattle: With over a decade serving Seattle homeowners, we bring proven craftsmanship to every Accessory Dwelling Unit project. From solid structural work to precise finishes, our team builds attached and detached ADUs designed for durability, comfort, and lasting value.

Home Additions in Seattle: We specialize in high-quality home additions that meet practical needs while upholding our standards for fine construction. Whether you need extra bedrooms, a functional home office, or a dedicated in-law suite, our local knowledge and hands-on approach ensure a result you’ll appreciate for years.

Professional Home Addition Contractor and ADU builder

Let's Talk About Your Remodeling Project

Complimentary Estimate and Expert Guidance from experienced Professionals.

Our ADU and Addition Services

Attached ADUs

Connected to the main house for multi-gen living or rental income. Designed for a seamless tie-in and code compliance.

Detached ADUs

Stand-alone backyard cottages for guests or rental. Built for privacy, durability, and local zoning compliance.

Home Additions

Increase square footage with custom additions that match your home’s style and boost long-term value.

Home Extensions

Targeted expansions: kitchen, bathrooms, living, or sunroom planned for comfort, light, and energy efficiency.

GALLERY

Some Previous Successful Home Extensions Projects in Seattle, WA

Why Choose BLC Remodeling LLC for Your Seattle Home Additions and ADUs?

Licensed and Insured Seattle Contractor

We are fully licensed and insured to handle home additions and ADUs throughout Seattle, meeting both Washington State requirements and the city’s specific building standards.

Experienced with Seattle’s Diverse Housing Styles

From historic Craftsman homes to modern townhouses, we adapt designs to suit each property’s character and the requirements of its neighborhood.

Functional Spaces for Urban Living

We have built basement ADUs, rooftop additions, and compact extensions designed to maximize every square foot in Seattle’s dense housing market.

Quality Construction for Lasting Performance

Our work includes reinforced framing, moisture protection systems, and precision finish work to ensure both durability and refined appearance.

Over a Decade Serving Seattle Homeowners

Since 2011, we have completed projects across Seattle neighborhoods including Ballard, Capitol Hill, and West Seattle, delivering results that combine structural strength with aesthetic appeal.
kitchen-remodeling-bellevue

Schedule an Estimate

Looking for a local Home Extension contractor in Seattle? Contact us today to schedule a free consultation, and let us transform your home with our custom remodeling services.

Achieve Your Dream Home With Our Process

Simplified Seattle Home Extension Process

1.

Schedule a Consultation

Reach out to us via phone or our contact forms .

2.

In-Home Assessment

We’ll schedule a visit to your home to understand your vision

3.

Receive a Detailed Quote

We’ll provide a detailed quote and project timeline.

4.

Schedule and Begin Work

Once you approve the quote, we'll schedule your project and begin the work.

Start Your Home Transformation Today

Schedule Your Seattle ADU or Addition Estimate

Call us anytime, we strive to answer all inquiries within 24 hours.

4.9
Based on 37 reviews
powered by Google
Christine S
23:28 16 Sep 25
The BLC team did a fantastic job on my bathroom. I was impressed by the transparency of the quote and the accurate estimation of the time it would take to complete the job. I appreciated the consistency in the crew that worked in my home and the fact that they were all employees. This was my first remodel so I was nervous about the process. I’m thrilled with results and have already booked the team to remodel another bathroom. Very strongly recommend!

Estimate Request Form

Frequently asked questions

Adding a 1,000 square foot addition to a home in Seattle generally costs between $85,000 and $220,000. The total cost depends on design complexity, material choices, and local permit requirements​

Adding an addition to your existing home is generally more cost-effective than building a new house. Home additions make use of existing infrastructure and utilities, which can significantly reduce costs. However, the total expense will depend on the size and complexity of the addition, as well as the materials used.

The cheapest type of home addition is typically a single-room extension, such as a sunroom or a small bedroom. These additions require less structural work and fewer materials compared to multi-room additions or second-story expansions. Costs can be further minimized by choosing cost-effective materials and designs.

The timeline for home additions varies depending on the project’s scope and complexity. On average, a small addition like a single room can take 3-4 months, while larger projects, such as adding a second story, can take 6-9 months. Detailed planning and efficient project management are crucial to staying on schedule.

Seattle’s requirements for ADUs include:

  • Size: ADUs can be up to 1,000 sq. ft. or 40% of the main dwelling’s floor area.
  • Parking: No additional parking is required if within a half-mile of frequent transit service; otherwise, one parking space is required.
  • Compliance: Must adhere to all applicable building codes and zoning regulations.

Visit the Seattle City Government website for more information.

Service Areas

Other Service Areas

Don’t see your neighborhood listed? No problem! We are eager to hear about your project. Call us today, and let’s discuss how we can help. Proudly serving homeowners throughout Eastside and Greater Seattle!