Mercer Island, WA · Additions
MODERN ADDITIONS Builder in Mercer Island, WA
Additions are where most contractors get into trouble — roof tie-ins, foundation underpinning, and continuity of the weather envelope are unforgiving details. We treat additions like new construction grafted onto an existing home, with engineered connections and fully blended exteriors.
Build timeline
Project dependent
Typical sqft
Custom
Mercer Island cost
$251K – $855K
Permit window
12–16 wk
What modern additions looks like in Mercer Island
MODERN ADDITIONS projects in Mercer Island are shaped by local zoning (R-8.4 / R-9.6 / R-12), a lot minimum of 8,400 sqft, and the kinds of sites we see day-to-day: North End, First Hill, Mid-Island. Below is what every Mercer Island Additions project from Golden State includes — fixed-price, one contract, one warranty.
- ✓Structural + foundation engineering
- ✓Roof + envelope tie-in detailing
- ✓Underpinning where required
- ✓Selective demolition + protection
- ✓New space framing, MEP, finish
- ✓Whole-home punch list
Other services in Mercer Island
More from Golden State ADU in Mercer Island
DADU
DETACHED ADU in Mercer Island
Stand-alone backyard cottages built from the ground up — engineered for rental income, multi-generational living, or your home office.
AADU
ATTACHED ADU in Mercer Island
Seamlessly integrated additions — basement, ground-floor, or wing conversions that maintain the architectural integrity of your existing home.
Garage
GARAGE CONV. in Mercer Island
Convert an under-used garage into a high-end studio, office, or rental quarter without surrendering your driveway.
GC
GENERAL CONTRACTING in Mercer Island
Full-service general contracting for remodels, renovations, and ground-up custom homes throughout the Puget Sound region.
Feasibility
FEASIBILITY STUDIES in Mercer Island
Before you commit, we analyze zoning, lot coverage, setbacks, utilities, and ROI so you have a real number — not a guess.
MODERN ADDITIONS across the Puget Sound
MODERN ADDITIONS builders in nearby cities
Start your Mercer Island Additions feasibility
$1,500 buys lot analysis, Mercer Island zoning verification, and a fixed price you can build a budget on.
Request Mercer Island feasibilityFrequently asked
What is included in MODERN ADDITIONS in Mercer Island?
Our MODERN ADDITIONS in Mercer Island scope includes design through completion: feasibility, schematic design, construction documents, permit submittal and review management, construction with one self-performed framing crew plus L&I-licensed MEP subcontractors, all required WA inspections, certificate of occupancy, and warranty. One contract, one license number, one warranty — not a coordination headache across five vendors.
How is MODERN ADDITIONS in Mercer Island different from a generic remodel?
MODERN ADDITIONS in Mercer Island carries code, permit, and construction details that a one-off remodeler hasn't repeated enough times to optimize. Examples: IECC R406 envelope path selection, fire separation when units are within 5 ft, side-sewer slope requirements, IRC Appendix AQ when permitted as a tiny house, separate utility metering rules. We do this scope every month — repetition is what makes our first-cycle approval rate and our schedule reliability stand out.
What is the typical price range for MODERN ADDITIONS in Mercer Island?
MODERN ADDITIONS in Mercer Island pricing in 2026 lands in the $295–$465/sqft all-in range depending on size, lot conditions, finish tier, and AHJ. The wide range is real — small lots with difficult access, soils requiring pier-and-beam, or service upgrades push the upper end; flat lots with good access and a catalog plan land at the lower end. Our feasibility report gives you a ±15% number tailored to your specific lot in two weeks.