ADU & Custom Home Addition Builders in Mercer Island, WA
Since 2011
Serving Bellevue
and the Eastside
Licensed & Insured
Company UBI
#604013490
BBB A+ Rated
Accredited and
Verified Business
4.9 ★ Google
Based on verified
Reviews
ADU & Addition Projects Built by BLC Remodeling in Mercer Island
Attached ADUs
Connected to the main home and built as part of the existing structure. We construct attached ADUs for homeowners who want additional living space for family, guests, or rental use, focusing on proper structural integration, shared systems, and layouts that make the new space feel like a natural extension of the house.
Detached ADUs
Stand-alone living units built separately from the main home. We construct backyard cottages and independent structures for homeowners who want private guest space, rental use, or long-term living areas, focusing on solid construction, functional layouts, and a finished result that works as a true second dwelling on the property.
Home Additions
Home additions are permanent extensions of the existing house, built as integrated parts of the structure. We construct expanded kitchens, additional bathrooms, new bedrooms, home offices, sunrooms, and in-law suites that extend the floor plan and become part of the original home—not separate or temporary spaces.
Garage & Basement
Garage and basement projects convert existing parts of the home into usable living space. We build finished rooms, living areas, offices or secondary suites by structurally adapting the space and constructing it as permanent, habitable square footage within the home.
Every ADU and home addition we build is a custom residential construction project. Our process is hands-on, detail-focused, and guided by craftsmanship, material quality, and building methods suited to homes in the Pacific Northwest.
How We Build ADUs & Home Additions
Designed Around Mercer Island Homes
Neighborhoods We Serve in Mercer Island
Building an ADU or addition in Mercer Island often involves working within specific residential and zoning conditions, including:
- ADUs are allowed on Mercer Island, and the city’s interim standards allow up to two ADUs per lot (attached, detached, or a combination) in many residential situations.
- ADU size is limited to 1,000 sq ft, and Mercer Island also ties ADU size to the primary home (25% of the primary home’s gross floor area), which shapes design early.
- Additions and conversions require permits and inspections; basements and garages also need to meet habitable-space requirements, including a minimum ceiling height of 6 ft 8 in.
Permitting and Local Coordination
- City planning and review processes
- Neighborhood-specific development requirements
- Homeowner associations, where applicable
*When approvals are needed, we follow local requirements and coordinate with the appropriate professionals.
If your home presents unique challenges, we’re happy to talk through them.
About BLC Remodeling
With over 14 years of residential building experience, BLC Remodeling is a Bellevue-based contractor and a trusted choice for custom ADUs and home additions across the Greater Seattle area. We focus on craftsmanship and attention to detail—from structural tie-ins to clean, precise finishes—ensuring every project is planned well and built with care.
We construct attached and detached ADUs, home extensions, new bedrooms, expanded kitchens, offices, in-law suites, and garage or basement conversions. Our team values clear communication and accurate execution, making sure the new space fits naturally with the home. Our local experience across the Eastside helps us understand each property and deliver results homeowners can rely on.
60 reviews
Custom Residential Remodeling with Quality Craftsmanship for Real Homes
Main Floor & Bathroom Remodel
Deck Construction
Full Kitchen Remodel
Some of Our Projects in Mercer Island
Questions about ADUs, Additions and Conversions in Mercer Island
How long does an ADU or home addition project usually take in Mercer Island?
Do garage and basement conversions require special approvals in Mercer Island?
What types of spaces can be included in an ADU or a home addition?
An ADU or home addition can include bedrooms, bathrooms, kitchens, living areas, home offices, storage, laundry rooms, and private entries. Layouts depend on the property and design goals, but the goal is always to create a fully usable extension of the home that fits everyday living.
What is the difference between an ADU and a DADU?
An ADU is a secondary living unit that’s attached to the main house or built within the existing structure, such as a basement or over-garage unit. A DADU is a detached version placed elsewhere on the property, often in the backyard or above a standalone garage. Both can include full living features such as a kitchen, bathroom, sleeping area, and private entrance.
Is a Detached ADU the same as a DADU?
Yes. A DADU is simply the term some Washington cities use for a Detached ADU. Both refer to a standalone living unit that is separate from the main house, often built in the backyard or above a garage. The structure functions as an independent dwelling with its own entrance and living features. We use “Detached ADU” on our website because it’s clearer and easier for homeowners to understand.